ALX Africa Software Engineering Programme Answers Student guide

0x00. C - Hello, World

Quiz questions

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Question #0

Which of the following are both valid comment syntaxes in ANSI C, and Betty-compliant?

```
/*
 * Comment
 */
```
```
# Comment
    
```
```
/* Comment */
    
```
```
/* Comment /* nested */ */
    
```
```
// Comment
    
```
```
/*
Comment
*/
```

Question #1

What is the common extension for a C header file?

.ch
.header
.hpp
.h

Question #2

What are the different steps to form an executable file from C source code

Compilation and linking
Interpretation, compilation and assembly
Preprocessing and compilation
Preprocessing, compilation, assembly, and linking
Interpretation, assembly and compilation

Question #3

In which category belongs the C programming language?

Compiled language
Interpreted language

Question #4

Which command can be used to compile a C source file?

c-compiler
gcc
bash

Question #5

What is the common extension for a C source file?

.py
.txt
.c
.cpp

0x01. C - Variables, if, else, while

Quiz questions

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Question #0

Which of the following are valid for statements in ANSI C and Betty-compliant? (Considering a and b two variables of type int)

Please select all correct answers

a = 0;
for (a < b;;)
{
    printf("%d\n", a++);
}

for (a = 0; a < b; a++)
{
    printf("%d\n", a);
}

a = 0;
for (; a < b;)
{
    printf("%d\n", a++);
}

for (a = 0; a < b; a++)
    printf("%d\n", a);

for (int a = 0; a < b; a++)
{
    printf("%d\n", a);
}

Question #1

What is the size of the float data type?

8 bytes
1 byte
2 bytes
4 bytes

Question #2

Which of the following are valid while or do/while statements in ANSI C and Betty-compliant? (Considering a and b two variables of type int)

Please select all correct answers

a = 0;
while (a < b)
    printf("%d\n", a++);

a = 0;
while (a < b)
(
    printf("%d\n", a);
    a++;
)

while (a = 0; a < b; a++)
{
    printf("%d\n", a);
}

a = 0;
do while (a < b)
{
    printf("%d\n", a);
    a++;
}

a = 0;
while (a < b)
{
    printf("%d\n", a);
    a++;
}

a = 0;
do {
    printf("%d\n", a);
    a++;
} while (a < b);

Question #3

What is the size of the unsigned int data type?

8 bytes
1 byte
2 bytes
4 bytes

Question #4

Which of the following are valid if statements in ANSI C and Betty-compliant? (Considering a and b two variables of type int)

Please select all correct answers

```
if ((((((a > b))))))
{
  return (a);
}
```
```
if a > b
{
  return (a);
}
```
```
if (a > b)
  return (a);
```
```
if (a > b)
{
  return (a);
}
```
```
if {a > b}
(
  return {a};
)
```

Question #5

What is the size of the char data type?

8 bytes
1 byte
2 bytes
4 bytes

0x02. C - Functions, nested loops

Quiz questions

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Question #0

What is the ASCII value of 0?

Question #1

What is the result of 12 % 10?

Question #2

What is the ASCII value of a?

Question #3

What is the result of 12 % 2?

Question #4

What is the ASCII value of 5?

Question #5

What is the ASCII value of -?

Question #6

Which of these loop statements don’t exist?

do... while
loop_to
for
each
while
foreach

Question #7

What is the ASCII value of J?

Question #8

What is the result of 12 % 3?

Question #9

What is the result of 89 % 7?

Question #10

What is the ASCII value of A?

0x03. C - Debugging

Quiz questions

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Question #0

The following code gives this output. What is the error?

carrie@ubuntu:/debugging$ cat main.c
#include <stdio.h>                                                                                  

/**                                                                                                 
  * main - debugging example                                                                         
  * Return: 0                                                                                        
  */                                                                                                 
int main(void)                                                                                      
{                                                                                                   
        int i;                                                                                      
        int j;                                                                                      
        int k;                                                                                      

        i = 0;                                                                                      
        j = 1000;                                                                                   
        while (i < j)                                                                               
        {                                                                                           
                k = j / 98;                                                                         
                i = i + k;                                                                          
                printf("%d\n", i);                                                                  
                j == j - 1;                                                                         
        }                                                                                           

        return (0);                                                                                 
}                                                                                                   
carrie@ubuntu:/debugging$

carrie@ubuntu:/debugging$ gcc -Wall -Werror -Wextra -pedantic main.
c                                                                                                   
main.c: In function ‘main’:                                                                         
main.c:20:3: error: statement with no effect [-Werror=unused-value]                                 
    j == j - 1;                                                                                      
    ^                                                                                                
cc1: all warnings being treated as errors                                                           
carrie@ubuntu:/debugging$

We don’t need to assign a new value to j because it doesn’t do anything
We want to assign j a new value, not compare it, so it should be j = j - 1 instead of j == j - 1
We want to compare j so we need an if statement before j == j - 1

Question #1

Look at the following code.

carrie@ubuntu:/debugging$ cat main.c
#include <stdio.h>                                                                                  

/**                                                                                                 
  * main - debugging example                                                                         
  * Return: 0                                                                                        
  */                                                                                                 
int main(void)                                                                                      
{                                                                                                   
        char *hello = "Hello, World!";                                                              

        for (i = 0; hello[i] != '\0'; i++)                                                          
        {                                                                                           
                printf("%c", hello[i]);                                                             
        }                                                                                           

        printf("\n");                                                                               

        return (0);                                                                                 
}                                                                                                   
carrie@ubuntu:/debugging$

carrie@ubuntu:/debugging$ gcc -Wall -Werror -Wextra -pedantic main.
c                                                                                                   
main.c: In function ‘main’:                                                                         
main.c:11:7: error: ‘i’ undeclared (first use in this function)                                     
  for (i = 0; hello[i] != '\0'; i++)                                                                
        ^                                                                                            
main.c:11:7: note: each undeclared identifier is reported only once for each function it appears in
main.c:9:8: error: variable ‘hello’ set but not used [-Werror=unused-but-set-variable]              
  char *hello = "Hello, World!";                                                                    
        ^                                                                                           
cc1: all warnings being treated as errors                                                           
carrie@ubuntu:/debugging$

In the main.c file, on what line is the first error that the compiler returns?

Tips:

You do not have to know exactly what this code does yet (but you will soon!).

Question #2

This code doesn’t work as intended.

#include "main.h"

/**
* main - prints even numbers from 0 to 100
* Return: 0
*/

int main(void)
{
        int i;

        for (i = 0; i < 100; i++)
        {
                if (i % 2 != 0)
                {
                        continue;
                }
                else
                {
                        break;
                }

                printf("%d\n", i);
        }

        return(0);
}

Let’s add printf statements to the code. What information do the printf statements tell us about how our code is executed?

#include "main.h"

/**
* main - prints even numbers from 0 to 100
* Return: 0
*/

int main(void)
{
        int i;

        printf("Before loop\n");

        for (i = 0; i < 100; i++)
        {
                if (i % 2 != 0)
                {
                        printf("i is not even so don't print\n");
                        continue;
                }
                else
                {
                        printf("i is even, break to print\n");
                        break;
                }

                printf("Outside of if/else, still inside for loop\n");

                printf("%d\n", i);
        }

        printf("For loop exited\n");

        return(0);
}

A printf statement shows that there is an infinite loop in the code
A printf statement shows when the for loop is finished
A printf statement shows exactly how many times the loop executes
printf statements shows that break will cause “For loop exited” to print, indicating that the even number is never printed

Question #3

The following code gives this incorrect output. Which of the following statements about what is causing the error is true?

carrie@ubuntu:/debugging$ cat main.c
#include <stdio.h>                                                                                 

/**                                                                                                
  * main - debugging example                                                                        
  * Return: 0                                                                                       
  */                                                                                                
int main(void)                                                                                     
{                                                                                                  
        int i;                                                                                     
        int j;                                                                                     

        for (i = 0; i < 10; i++)                                                                   
        {                                                                                          
                j = 0;                                                                             
                while (j < 10)                                                                     
                {                                                                                  
                        printf("%d", j);                                                           
                }                                                                                  
                printf("\n");                                                                      
        }                                                                                          

        return (0);                                                                                
}                                                                                                  
carrie@ubuntu:/debugging$

carrie@ubuntu:/debugging$ gcc -Wall -Werror -Wextra -pedantic main.c
carrie@ubuntu:/debugging$ ./a.out
0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000 <...>
^Ccarrie@ubuntu:/debugging$

j never increments so it will always be less than 10
j is always equal to i so the loop will never end
j never increments so it is always going to print 0

0x04. C - More functions, more nested loops

Quiz questions

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Question #0

What is the output of the following piece of code?

int i;

i = -9;
while (i < 0)
{
    printf("%d", -i);
    i++;
}

-9-8-7-6-5-4-3-2-1
9876543210
987654321
-9-8-7-6-5-4-3-2-10

Question #1

What is the output of the following piece of code?

int i;

for (i = 0; i < 10; i++)
{
    printf("%d", i * 2);
}

0123456789
2468101214161820
024681012141618

Question #2

What is the return value of the following function?

int some_function(void)
{
    printf("%d", 12);
    return (98);
}

Question #3

What is the output of the following piece of code?

int i;

i = 9;
while (--i)
{
    printf("%d", i);
}

987654321
87654321
9876543210
876543210

Question #4

What is the output of the following piece of code?

int i;

i = 9;
while (i--)
{
    printf("%d", i);
}

987654321
87654321
876543210
9876543210

Question #5

What is the output of the following piece of code?

int i;

for (i = 48; i < 58; i++)
{
    printf("%c", i);
}

48495051525354555657
0123456789
School

Question #6

What is the output of the following piece of code?

int i;

i = 0;
while (i < 10)
{
    i++;
    printf("%d", i / 2);
}

0011223344
0123456789
0112233445

Question #7

What is the return value of the following function?

int some_function(void)
{
    int i;

    for (i = 0; i < 10; i++)
    {
        printf("%d", i);
    }
    return(i);
}

0123456789
0
9
10

Question #8

What is the output of the following piece of code?

int i;

i = 0;
while (i < 10)
{
    printf("%d", i % 2);
    i++;
}

0101010101
0123456789
1010101010

0x05. C - Pointers, arrays and strings

Quiz questions

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Question #0

The process of getting the value that is stored in the memory location pointed to by a pointer is called:

Casting
Pointing
Accessing
Dereferencing

Question #1

What is the value of n after the following code is executed?

int n = 98;
int *p = &n;

*p = 402;

Question #2

If we have a variable called var of type int, how can we get its address in memory?

*var
*(var)
&var

Question #3

What is the value of n after the following code is executed?

int n = 98;
    int *p = &n;

Question #4

What happens when one tries to access an illegal memory location?

There’s a chance for the computer to catch fire, and sometimes even explode
The operation is ignored
Segmentation fault
The computer shuts down

Question #5

We declare the following variable

int arr[5];

What is the size in memory of the variable arr?

10 bytes
32 bytes
4 bytes
20 bytes
5 bytes
8 bytes

Question #6

Is it possible to declare a pointer to a pointer?

Yes
No
It depends on the type the pointer is pointing to

Question #7

What is the size of a pointer to a char (on a 64-bit architecture)

8 bytes
1 byte
2 bytes
4 bytes

Question #8

What is the identifier to print an address with printf?

Question #9

What is the value of n after the following code is executed?

int n = 98;
    int *p = &n;
    
    p = 402;

Question #10

What is the value of n after the following code is executed?

int n = 98;
    int *p = &n;
    
    *p++;

Question #11

We declare the following variable

int arr[5];

What is the equivalent of typing arr[2]?

arr + 2
*arr + 2
*(arr + 2)

Question #12

What is the size of a pointer to an int (on a 64-bit architecture)

8 bytes
1 byte
2 bytes
4 bytes

0x06. C - More pointers, arrays and strings

Quiz questions

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Question #0

Why is it important to reserve enough space for an extra character when declaring/allocating a string?

For fun
In case we need one
For memory alignment
For the null byte (end of string)

Question #1

What is wrong with the following code?

int n = 5;
    int array[n];
    int i = 3;
    
    array[n] = i;

It is not possible to access array[n]
Nothing is wrong
It is impossible to declare the variable array this way
The array array is not entirely initialized

Question #2

What happens when one tries to dereference a pointer to NULL?

World War Z
Nothing
Segmentation fault
Kernel panic

Question #3

What is/are the difference(s) between the two following variables? (Except their names)

char *s1 = "";
    char *s2 = NULL;

The first one can be dereferenced, not the second one
They are the same
The second one can be dereferenced, not the first one
The first one points to a 0-byte, the second one points to 0
The first one points to 0, the second one points to a 0-byte

Question #4

var = "Best";

What is the type of var?

string
char *
int *

Question #5

What is wrong with the following code?

int n = 5;
    int array[5];
    int i = 3;
    
    array[n] = i;

It is not possible to access array[n]
Nothing is wrong
It is impossible to declare the variable array this way
The array array is not entirely initialized

Question #6

What is wrong with the following code?

int n = 5;
    int array[10];
    int i = 3;
    
    array[n] = i;

It is not possible to access array[n]
Nothing is wrong
It is impossible to declare the variable array this way
The array array is not entirely initialized

0x07. C - Even more pointers, arrays and strings

Quiz questions

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Question #0

In this following code, what is the value of a[3][1]?

int a[5][2] = {{1, 2}, {3, 4}, {5, 6}, {7, 8}, {9, 10}};

8
7
9
{7, 8}

Question #1

In this following code, what is the value of a[0][0]?

int a[5][2] = {{1, 2}, {3, 4}, {5, 6}, {7, 8}, {9, 10}};

Question #2

What is the size of *p in this code?

int *p;

4 bytes
8 bytes
16 bytes

Question #3

What is the size of *p in this code?

int **p;

4 bytes
8 bytes
16 bytes

Question #4

In this following code, what is the value of a[1][1]?

int a[5][2] = {{1, 2}, {3, 4}, {5, 6}, {7, 8}, {9, 10}};

Question #5

What is the size of p in this code?

int *p;

4 bytes
8 bytes
16 bytes

Question #6

In this following code, what is the value of a[3][0]?

int a[5][2] = {{1, 2}, {3, 4}, {5, 6}, {7, 8}, {9, 10}};

5
7
8
{7, 8}

Question #7

What is stored inside a pointer to a pointer to an int?

An address where an int is stored
An int
An address where an address is stored

Question #8

What is the size of p in this code?

int **p;

4 bytes
8 bytes
16 bytes

0x08. C - Recursion

Quiz questions

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Question #0

What does this code print?

int print(int nb)
    {
        if (nb < 0) 
        {
            return (0);
        }
        printf("%d", nb + print(nb - 1));
        nb --;
        return (nb);
    }
    
    int main(void)
    {
        print(4);
        return (0);
    }

64200
00246
01234568

Question #1

What does this code print?

void print(int nb)
    {
        printf("%d", nb);
        nb ++;
        if (nb < 10) 
        {
            print(nb);
        }
    }
    
    int main(void)
    {
        print(4);
        return (0);
    }

456789
987654
109876543
345678910

Question #2

What does this code print?

void print(int nb)
    {
        printf("%d", nb);
        nb --;
        if (nb > 0) 
        {
            print(nb);
        }
    }
    
    int main(void)
    {
        print(2);
        return (0);
    }

Question #3

What does this code print?

void print(int nb)
    {
        if (nb < 0) 
        {
            return;
        }
        printf("%d", nb);
        nb --;
        print(nb);
    }
    
    int main(void)
    {
        print(4);
        return (0);
    }

4321
01234
43210
1234

Question #4

What does this code print?

void print(int nb)
    {
        printf("%d", nb);
        -- nb;
        if (nb > 0) 
        {
            print(nb);
        }
    }
    
    int main(void)
    {
        print(4);
        return (0);
    }

3210
4321
43210
321

0x09. C - Static libraries

Quiz questions

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Question #0

What command(s) can be used to list the symbols stored in a static library?

ld
nm
ranlib
ar

Question #1

What command is used to create a static library from object files?

ar
gcc
nm
ld
ranlib

Question #2

What is the format of a static library?

An archive
A relocatable ELF file
An executable ELF file
A shared ELF file

Question #3

What is the point of using ranlib?

List the content of a library
Creating an archive
Indexing an archive
Create a library from a simple archive

0x0A. C - argc, argv

Quiz questions

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Question #0

In the following command, what is argv[2]?

$ ./argv My School is fun

is fun
My School is fun
is
My School
School
NULL
fun
./argv
My

Question #1

What is argv[0]

The program name
NULL
It does not always exist
The first command line argument

Question #2

In the following command, what is argv[2]?

$ ./argv "My School is fun"

is fun
My School is fun
is
My School
School
NULL
fun
./argv
My

Question #3

In the following command, what is argv[2]?

$ ./argv "My School" "is fun"

is fun
My School is fun
is
My School
School
NULL
fun
./argv
My

Question #4

What is argc?

The length of the first command line argument
The number of command line arguments
A flag set to 1 when command line arguments are present
The size of the argv array

Question #5

What is argv[argc]?

The program name
NULL
The last command line argument
It does not always exist
The first command line argument

Question #6

What is argv?

An array containing the program compilation flags
An array containing the program command line arguments
An array of size argc

0x0B. C - malloc, free

Quiz questions

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Question #0

How many bytes will this statement allocate?

malloc(sizeof(char) * 10)

Question #1

How many bytes will this statement allocate?

malloc(sizeof(int) * 10)

Question #2

How many bytes will this statement allocate?

malloc((sizeof(char) * 10) + 1)

Question #3

How many bytes will this statement allocate?

malloc(10)

Question #4

What is Valgrind?

It’s a program to test a C program in a specific environment
A container service
It’s a program to validate memory allocation
It’s a new step when I compile with gcc

Question #5

How many bytes will this statement allocate?

malloc(sizeof(unsigned int) * 2)

Question #6

How many bytes will this statement allocate?

malloc(sizeof(int) * 4)

0x0C. C - More malloc, free

Quiz questions

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Question #0

What is wrong with this code:


  
  int cp(void)
  {
      char *s;
  
      s = malloc(12);
      strcpy(s, "Best School");
      return (0);
  }

malloc can fail so we should check its return value all the time before using the pointers returned by the function.
You don’t have enough space to store the copy of the string “Best School”
There is no comment
You can’t call strcpy with a string literal

Question #1

What will you see on the terminal?

int main(void)
  {
      int *ptr;
  
      *ptr = 98;
      printf("%d\n", *ptr);
      return (0);
  }

Segmentation Fault
0
98
It doesn’t compile

Question #2

malloc returns a pointer

False
True

Question #3

You can do this:

char *s;
  
  s = strdup("Best School");
  if (s != NULL)
  {
      free(s);
  }

Question #4

You can do this:

char str[] = "Best School";
  
  free (str);

Question #5

You can do this:

free("Best School");

Question #6

To allocate enough space for an array of 10 integers (on a 64bit, Linux machine), I can use:

malloc(64 * 10)
malloc(10 * int)
malloc(10 * sizeof(int))

Question #7

malloc returns an address

False
True

Question #8

The memory space reserved when calling malloc is on:

The heap
The stack

Question #9

If I want to copy the string “Best School” into a new space in memory, I can use this statement to reserve enough space for it (select all valid answers):

malloc(12)
malloc(sizeof(“Best School”) + 1)
malloc(sizeof(“Best School”))
malloc(strlen(“Best School”) + 1)
malloc(strlen(“Best School”))
malloc(11)

0x0D. C - Preprocessor

Quiz questions

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Question #0

This portion of code is actually using the library stdlib.

#include <stdlib.h>

False
True

Question #1

The macro __FILE__ expands to the name of the current input file, in the form of a C string constant.

False
True

Question #2

This code will try to allocate 1024 bytes in the heap:

#define BUFFER_SIZE 1024
  malloc(BUFFER_SIZE)

False
True

Question #3

The preprocessor generates object code

False
True

Question #4

NULL is a macro

False
True

Question #5

What is the gcc option that runs only the preprocessor?

-cisfun
-preprocessor
-E
-pedantic
-a
-P
-p

Question #6

This is the correct way to define the macro SUB:

#define SUB(a, b) a - b

No, it should be written this way:
```
#define SUB(a, b) ((a) - (b))
  
```
Yes
No, it should be written this way:
```
#define SUB(a, b) (a - b)
  
```
No, it should be written this way:
```
#define SUB(a, b) (a) - (b)
  
```

Question #7

The preprocessor removes all comments

False
True

Question #8

What are the steps of compilation?

1.compiler 2. preprocessor 3. assembler 4. linker
1.preprocessor 2.compiler 3. assembler 4. linker
1.preprocessor 2.compiler 3. linker 4. assembler

Question #9

The preprocessor links our code with libraries.

False
True

Question #10

What will be the last 5 lines of the output of the command gcc -E on this code?

#include <stdlib.h>
  
  int main(void)
  {
      NULL;
      return (EXIT_SUCCESS);
  }

int main(void)
  {
   '\0';
   return (0);
  }

int main(void)
  {
   0;
   return (0);
  }

int main()
  {
   0;
   return (0);
  }

int main(void)
  {
   ((void *)0);
   return (0);
  }

Question #11

What does the macro TABLESIZE expand to?

#define BUFSIZE 1020
  #define TABLESIZE BUFSIZE
  #undef BUFSIZE
  #define BUFSIZE 37

1020
37
nothing

Question #12

Why should we use include guards in our header files?

To avoid the problem of double inclusion when dealing with the include directive.
Because we said so, and we should never ask why.

Question #13

The preprocessor generates assembly code

False
True

Question #14

What will be the output of this program? (on a standard 64 bits, Linux machine)

#include <stdio.h>
  #include <stdlib.h>
  
  #define int char
  
  int main(void)
  {
      int i;
  
      i = 5;
      printf ("sizeof(i) = %lu", sizeof(i));
      return (EXIT_SUCCESS);
  }

sizeof(i) = 5
sizeof(i) = 4
Segmentation Fault
sizeof(i) = 1
It does not compile
sizeof(i) = 8

0x0E. C - Structures, typedef

Quiz questions

Great! You've completed the quiz successfully! Keep going! (Hide quiz)

Question #0

Those two codes do the same thing:

typedef struct point point;
  struct point {
     int    x;
     int    y;
  };
  point p = {1, 2};

typedef struct point point;
  struct point {
     int    x;
     int    y;
  };
  point p = { .y = 2, .x = 1 };

True
False: the second does not compile
False: the members of the structures will not have the same values

Question #1

You should write documentation for all the structures you create

True
I’ll do it 5 minutes before the deadline when I try Betty on my header file
As soon as I write my structure.

Question #2

Given this code:

struct point {
     int x;
     int y;
  };
  struct point my_point = { 3, 7 };
  struct point *p = &my_point;

To set the member y of my variable my_point to 98, I can do (select all valid answers):

(*p).y = 98;
my_point.y = 98;
p->y = 98;
my_point->y = 98;
p.y = 98;

Question #3

The general syntax for a struct declaration in C is:

struct tag_name {
     type member1;
     type member2;
     /* declare as many members as desired, but the entire structure size must be known to the compiler. */
  };

True
False
Maybe

0x0F. C - Function pointers

Quiz questions

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Question #0

What does a pointer to a function point to (check all correct answers if there is more than one)?

The first byte of code of the function
data
code
The first character of the name of the function

Question #1

If f is a pointer to a function that takes no parameter and returns an int, you can call the function pointed by f this way (check all correct answers if there is more than one):

f();
(*f)();
f;

Question #2

Which one is a pointer to a function?

(int *)func(int a, float b);
int func(int a, float b);
int *func(int a, float b);
int (*func)(int a, float b);

Question #3

This void (*anjula[])(int, float) is:

An array of pointers to functions that take an int and a float as parameters and returns nothing
A pointer to a function that takes an int and a float as parameters and returns nothing
A pointer to an array of functions that take an int and a float as parameters and returns nothing
A pointer to a function that takes an array of int and float as a parameter and returns nothing
A pointer to a function that takes an int and a float as parameters and returns an empty array

Question #4

To store the address of this function:

void neyo(void);

to the variable f of type pointer to a function that does not take any argument and does not return anything, you would do (check all correct answers if there is more than one):

*f = &neyo;
f = neyo;
f = &neyo;
*f = neyo;

0x12. C - Singly linked lists

Quiz questions

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Question #0

Arrays Vs Linked Lists: select all true statements

Memory is aligned for a Linked list - each elements are back to back in the memory
Memory is aligned for an Array - each elements are back to back in the memory
We can easily removed an element from a Linked list
We can easily remove an element from an Array
Array can contain as value a structure
We can add elements indefinitely to a linked list
We can add elements indefinitely to an array
Linked list can contain as value a structure

Question #1

What’s the “tail” of a linked list?

It’s the node with the lowest value
It’s the node with the pointer to the next equals to NULL
It’s the first node
It’s the node with the highest value

Question #2

What’s a node? (select all possible answers)

It’s an integer
It’s a server
It’s a space allocated in memory
It’s a structure with a pointer to the next node and value information
It’s a cell in an array

Question #3

In a singly linked list, what are possible directions to traverse it? (select all possible answers)

Backward
Forward

Question #4

What’s the “head” of a linked list?

It’s the node with the lowest value
It’s the last node
It’s the node with the pointer to the next equals to NULL
It’s the node with the highest value
It’s the first node

0x14. C - Bit manipulation

Quiz questions

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Question #0

0x66 & 0x22 = ?

0x22
0x44
0x66

Question #1

~ 0x98 = ?

0x66
0x67
0x68

Question #2

0x89 >> 3 = ?

0x11
0x89
0x08
0x44
0x22

Question #3

0x01 & 0x00 = ?

0x00
0x01
0x02

Question #4

0x88 & 0x01 = ?

0x89
0x00
0x01
0x88

Question #5

0x89 & 0x01 = ?

0x89
0x00
0x01
0x88

Question #6

0x13 << 1 = ?

0x98
0x13
0x26
0x4C

Question #7

0x44 | 0x22 = ?

0x22
0x44
0x66

Question #8

0x01 & 0x01 = ?

0x00
0x01
0x02

Question #9

0x01 | 0x00 = ?

0x00
0x01
0x02

Question #10

0x02 >> 1 = ?

0x02
0x01
0x00

Question #11

What is 0b001010010 in base10?

Question #12

What is 98 in base16?

0x62
0x98
0x96

Question #13

0x01 << 1 = ?

0x03
0x00
0x10
0x01
0x02

Question #14

What is 0b01101101 in base16?

0x7D
0x36
0xD6
0x6D
0x6E

Question #15

~ 0x12 = ?

0x21
0xED
0xFD
0xEE

Question #16

What is 98 in base2?

0b01010010
0b01100010
0b10011000

Question #17

What is 0x89 in base2?

0b10001000
0b10101001
0b10001001
0b01101001

Question #18

0x01 | 0x01 = ?

0x00
0x01
0x02

Question #19

What is 0x89 in base10?

0x15. C - File I/O

Quiz questions

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Question #0

What is the oflag used to open a file in mode read + write?

O_WRONLY
O_RDONLY
O_RDWR

Question #1

What happens if you try to write “Best” to the standard input on Ubuntu 14.04 LTS?

The text will be printed on the terminal on the standard output
Nothing
Segmentation fault
The text will be printed on the terminal but I can’t pipe it

Tips:

Just try it! :)

Question #2

What is the return value of the system call open if it fails?

0
-1
98

Question #3

What is the unistd symbolic constant for the Standard error?

STDIN_FILENO
STDOUT_FILENO
STDERR_FILENO

Question #4

What system call would you use to write to a file descriptor? (select all correct answers)

printf
fprintf
write

Question #5

is open a function or a system call? (select all valid answers)

it’s a function provided by the kernel
it’s a function
it’s a kernel routine
it’s a system call
it’s a library call

Question #6

why? #AlwaysAskWhy

Because this will be the third opened file descriptor for my process
Because most of the time, I will already have stdin (value 0), stdout (value 1) and stderr (value 2) opened when my program starts executing.
Because this will be the first opened file descriptor and in CS we start counting starting from 0
I don’t care I never ask why, just let me access the tasks!
Because this will be the first opened file descriptor and we start counting starting from 1
Because this will be the second opened file descriptor for my process

Question #7

What is the correct combination of oflags used to open a file with the mode write only, create it if it doesn’t exist and append new content at the end if it already exists?

O_RDWR | O_CREAT | O_APPEND
O_WRONLY
O_WRONLY | O_CREAT | O_EXCL
O_WRONLY | O_CREAT | O_APPEND

Question #8

What is the unistd symbolic constant for the standard input?

STDIN_FILENO
STDOUT_FILENO
STDERR_FILENO

Question #9

What is the oflag used to open a file with the mode read only?

O_WRONLY
O_RDONLY
O_RDWR

Question #10

Without context, on Ubuntu 14.04 LTS, write is a … (please select all correct answers):

game
executable
kernel routine
system call
library call

Question #11

Most of the time, on a classic, modern Linux system, what will be the value of the first file descriptor you will get after opening a new file with open (if open succeeds of course):

Question #12

Which of these answers are the equivalent of O_RDWR on Ubuntu 14.04 LTS? (select all correct answers):

1
3 & 2
3 | 2
(O_RDONLY && O_WRONLY)
(O_WRONLY << 1)
(O_RDONLY & O_WRONLY)
2
3
1 << 1
O_RDONLY
(O_RDONLY | O_WRONLY)
0
(O_RDONLY << 1)
O_WRONLY
(O_RDONLY + O_WRONLY)

Tips:

Use printf or read the headers to see the definitions/values of these macros.

Question #13

What is the unistd symbolic constant for the standard output?

STDIN_FILENO
STDOUT_FILENO
STDERR_FILENO

Question #14

When I am using O_WRONLY | O_CREAT | O_APPEND -> the | are bitwise operators.

False
True

0x1B. C - Sorting algorithms & Big O

Quiz questions

Great! You've completed the quiz successfully! Keep going! (Hide quiz)

Question #0

What is the time complexity of this function / algorithm?

var factorial = function(n) {
            if(n == 0) {
                return 1
            } else {
                return n * factorial(n - 1);
            }
        }

O(nlog(n))
O(2^n)
O(log(n))
O(n^2)
O(1)
O(n)
O(n!)

Question #1

What is the time complexity of “popping” an element in a queue if you are given a pointer to both the head and the tail of the queue?

O(log(n))
O(nlog(n))
O(1)
O(2^n)
O(n)
O(n!)

Question #2

What is the time complexity of setting the value of the nth element in a singly linked list? (Assuming you have a pointer to the node to set the value of)

O(nlog(n))
O(2^n)
O(log(n))
O(n^2)
O(1)
O(n)
O(n!)

Question #3

What is the time complexity of removing at index n in an unsorted array?

O(nlog(n))
O(2^n)
O(log(n))
O(n^2)
O(1)
O(n)
O(n!)

Question #4

What is the time complexity of this function / algorithm?

def func(n):
            a=5
            b=6
            c=10
            for i in range(n):
                for j in range(n):
                    x = i * i
                    y = j * j
                    z = i * j
            for k in range(n):
                w = a*k + 45
                v = b*b
            d = 33

O(nlog(n))
O(2^n)
O(log(n))
O(n^2)
O(1)
O(n)
O(n!)

Question #5

What is the time complexity of this function / algorithm?

void f(int n)
        {
            int i;
        
            for (i = 0; i < n; i += 98)
            {
                printf("[%d]\n", i);
            }
        }

O(nlog(n))
O(2^n)
O(log(n))
O(n^2)
O(1)
O(n)
O(n!)

Question #6

Assuming you have a pointer to the node to insert, what is the time complexity of inserting after the nth element of a doubly linked list?

O(nlog(n))
O(2^n)
O(log(n))
O(n^2)
O(1)
O(n)
O(n!)

Question #7

What is the time complexity of removing at index n from an unsorted Python 3 list?

O(nlog(n))
O(2^n)
O(log(n))
O(n^2)
O(1)
O(n)
O(n!)

Question #8

What is the time complexity of this function / algorithm?

void f(int n)
        {
            int i;
            int j;
        
            for (i = 0; i < n; i++)
            {
                if (i % 2 == 0)
                {
                    for (j = 1; j < n; j = j * 2)
                    {
                        printf("[%d] [%d]\n", i, j);
                    }
                }
                else
                {
                    for (j = 0; j < n; j = j + 2)
                    {
                        printf("[%d] [%d]\n", i, j);
                    }
                }
            }
        }

O(nlog(n))
O(2^n)
O(log(n))
O(n^2)
O(1)
O(n)
O(n!)

Question #9

What is the time complexity of this function / algorithm?

void f(unsigned int n)
        {
            int i;
            int j;
        
            for (i = 0; i < n; i++)
            {
                for (j = 1; j < n; j = j * 2)
                {
                    printf("[%d] [%d]\n", i, j);
                }
            }
        }

O(nlog(n))
O(2^n)
O(log(n))
O(n^2)
O(1)
O(n)
O(n!)

Question #10

What is the time complexity of accessing the nth element on an unsorted array?

O(nlog(n))
O(2^n)
O(log(n))
O(n^2)
O(1)
O(n)
O(n!)

Question #11

What is the time complexity of this function / algorithm?

foreach($numbers as $number)
        {
            echo $number;
        }

O(nlog(n))
O(2^n)
O(log(n))
O(n^2)
O(1)
O(n)
O(n!)

Question #12

What is the time complexity of the “push” operation onto a stack?

O(nlog(n))
O(2^n)
O(log(n))
O(n^2)
O(1)
O(n)
O(n!)

Question #13

What is the time complexity of this function / algorithm?

void f(int n)
        {
            printf("n = %d\n", n);
        }

O(nlog(n))
O(2^n)
O(log(n))
O(n^2)
O(1)
O(n)
O(n!)

Question #14

What is the time complexity of this function / algorithm?

void f(unsigned int n)
        {
            int i;
        
            for (i = 1; i < n; i = i * 2)
            {
                printf("[%d]\n", i);
            }
        }

O(nlog(n))
O(2^n)
O(log(n))
O(n^2)
O(1)
O(n)
O(n!)

Question #15

What is the time complexity of accessing the nth element of a doubly linked list?

O(nlog(n))
O(2^n)
O(log(n))
O(n^2)
O(1)
O(n)
O(n!)

Question #16

What is the time complexity of searching for an element in a doubly linked list of size n?

O(nlog(n))
O(2^n)
O(log(n))
O(n^2)
O(1)
O(n)
O(n!)

Question #17

What is the time complexity accessing the nth element in an unsorted Python 3 list?

O(nlog(n))
O(2^n)
O(log(n))
O(n^2)
O(1)
O(n)
O(n!)

Question #18

What is the time complexity of this function / algorithm?

int Fibonacci(int number)
        {
            if (number <= 1) return number;
        
            return Fibonacci(number - 2) + Fibonacci(number - 1);
        }

O(nlog(n))
O(2^n)
O(log(n))
O(n^2)
O(1)
O(n)
O(n!)

Question #19

What is the worst case time complexity of insertion in a hash table with the implementation you used during the previous Hash Table C project (chaining)?

O(nlog(n))
O(2^n)
O(log(n))
O(n^2)
O(1)
O(n)
O(n!)

Question #20

What is the time complexity of accessing the nth element of a singly linked list?

O(nlog(n))
O(2^n)
O(log(n))
O(n^2)
O(1)
O(n)
O(n!)

Question #21

What is the time complexity of searching for an element in a singly linked list of size n?

O(nlog(n))
O(2^n)
O(log(n))
O(n^2)
O(1)
O(n)
O(n!)

Question #22

What is the time complexity of setting value at index n in an unsorted Python 3 list?

O(nlog(n))
O(2^n)
O(log(n))
O(n^2)
O(1)
O(n)
O(n!)

Question #23

What is the time complexity of this function / algorithm?

void f(int n)
        {
             int i;
             int j;
        
             for (i = 0; i < n; i++)
             {
                  for (j = i + 1; j < n; j++)
                  {
                       printf("[%d] [%d]\n", i, j);
                  }
             }
        }

O(nlog(n))
O(2^n)
O(log(n))
O(n^2)
O(1)
O(n)
O(n!)

Question #24

What is the time complexity of “pushing” an element into a queue if you are given a pointer to both the head and the tail of the queue?

O(nlog(n))
O(2^n)
O(log(n))
O(n^2)
O(1)
O(n)
O(n!)

Question #25

What is the time complexity of inserting after the nth element of a singly linked list? (Assuming you have a pointer to the node to insert)

O(nlog(n))
O(2^n)
O(log(n))
O(n^2)
O(1)
O(n)
O(n!)

Question #26

What is the time complexity of inserting at index n on an unsorted array?

O(nlog(n))
O(2^n)
O(log(n))
O(n^2)
O(1)
O(n)
O(n!)

Question #27

What is the time complexity of removing the nth element of a singly linked list? (Assuming you have a pointer to the node to remove)

O(nlog(n))
O(2^n)
O(log(n))
O(n^2)
O(1)
O(n)
O(n!)

Question #28

What is the time complexity of searching for an element in a queue of size n if you are given a pointer to both the head and the tail of the queue?

O(nlog(n))
O(2^n)
O(log(n))
O(n^2)
O(1)
O(n)
O(n!)

Question #29

What is the time complexity of inserting into an unsorted Python 3 list at index n?

O(nlog(n))
O(2^n)
O(log(n))
O(n^2)
O(1)
O(n)
O(n!)

Question #30

Assuming you have a pointer to the node to set the value of, what is the time complexity of setting the value of the nth element in a doubly linked list?

O(nlog(n))
O(2^n)
O(log(n))
O(n^2)
O(1)
O(n)
O(n!)

Question #31

What is the time complexity of worst case deletion from a hash table with the implementation you used during the previous Hash Table C project (chaining)?

O(nlog(n))
O(2^n)
O(log(n))
O(n^2)
O(1)
O(n)
O(n!)

Question #32

What is the time complexity of searching for an element - worst case - in a hash table with the implementation you used during the previous Hash Table C project (chaining)?

O(nlog(n))
O(2^n)
O(log(n))
O(n^2)
O(1)
O(n)
O(n!)

Question #33

What is the time complexity of setting a value at index n in an unsorted array?

O(nlog(n))
O(2^n)
O(log(n))
O(n^2)
O(1)
O(n)
O(n!)

Question #34

What is the time complexity of this function / algorithm?

void f(int n)
        {
            int i;
        
            for (i = 0; i < n; i++)
            {
                printf("[%d]\n", i);
            }
        }

O(nlog(n))
O(2^n)
O(log(n))
O(n^2)
O(1)
O(n)
O(n!)

Question #35

What is the time complexity of searching for an element in an unsorted array of size n?

O(nlog(n))
O(2^n)
O(log(n))
O(n^2)
O(1)
O(n)
O(n!)

Question #36

What is the time complexity of searching for an element in a stack of size n?

O(nlog(n))
O(2^n)
O(log(n))
O(n^2)
O(1)
O(n)
O(n!)

Question #37

What is the best case time complexity of insertion in a hash table with the implementation you used during the previous Hash Table C project (chaining)?

O(nlog(n))
O(2^n)
O(log(n))
O(n^2)
O(1)
O(n)
O(n!)

Question #38

What is the best case time complexity searching for an element in a hash table with the implementation you used during the previous Hash Table C project (chaining)?

O(nlog(n))
O(2^n)
O(log(n))
O(n^2)
O(1)
O(n)
O(n!)

Question #39

What is the time complexity of the “pop” operation onto a stack?

O(nlog(n))
O(2^n)
O(log(n))
O(n^2)
O(1)
O(n)
O(n!)

Question #40

What is the time complexity of best case deletion from a hash table with the implementation you used during the previous Hash Table C project (chaining)?

O(nlog(n))
O(2^n)
O(log(n))
O(n^2)
O(1)
O(n)
O(n!)

Question #41

Assuming you have a pointer to the node to remove, what is the time complexity of removing the nth element of a doubly linked list?

O(nlog(n))
O(2^n)
O(log(n))
O(n^2)
O(1)
O(n)
O(n!)

Question #42

What is the time complexity of searching for an element in an unsorted Python 3 list of size n?

O(nlog(n))
O(2^n)
O(log(n))
O(n^2)
O(1)
O(n)
O(n!)