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0x02. C - Functions, nested loops

  • By Julien Barbier

Resources

Read or watch:

Learning Objectives

At the end of this project, you are expected to be able to explain to anyone, without the help of Google:

General

  • What are nested loops and how to use them
  • What is a function and how do you use functions
  • What is the difference between a declaration and a definition of a function
  • What is a prototype
  • Scope of variables
  • What are the gcc flags -Wall -Werror -pedantic -Wextra -std=gnu89
  • What are header files and how to to use them with #include

Requirements

General

  • Allowed editors: vi, vim, emacs
  • All your files will be compiled on Ubuntu 20.04 LTS using gcc, using the options -Wall -Werror -Wextra -pedantic -std=gnu89
  • All your files should end with a new line
  • A README.md file, at the root of the folder of the project is mandatory
  • Your code should use the Betty style. It will be checked using betty-style.pl and betty-doc.pl
  • You are not allowed to use global variables
  • No more than 5 functions per file
  • You are not allowed to use the standard library. Any use of functions like printf, puts, etc... is forbidden
  • You are allowed to use _putchar
  • You don't have to push _putchar.c, we will use our file. If you do it won't be taken into account
  • In the following examples, the main.c files are shown as examples. You can use them to test your functions, but you don't have to push them to your repo (if you do we won't take them into account). We will use our own main.c files at compilation. Our main.c files might be different from the one shown in the examples
  • The prototypes of all your functions and the prototype of the function _putchar should be included in your header file called main.h
  • Don't forget to push your header file

More Info

You do not have to understand the call by reference (address), stack, static variables, recursions or arrays, yet.

Tasks

0. _putchar

mandatory

Write a program that prints Holberton, followed by a new line.

  • The program should return 0
julien@ubuntu:~/0x02$  gcc -Wall -pedantic -Werror -Wextra -std=gnu89 _putchar.c 0-holberton.c -o 0-holberton
julien@ubuntu:~/0x02$ ./0-holberton
Holberton
julien@ubuntu:~/0x02$

Repo:

  • GitHub repository: alx-low_level_programming
  • Directory: 0x02-functions_nested_loops
  • File: 0-holberton.c

 Done? Help Get a sandbox

1. I sometimes suffer from insomnia. And when I can't fall asleep, I play what I call the alphabet game

mandatory

Write a function that prints the alphabet, in lowercase, followed by a new line.

  • Prototype: void print_alphabet(void);
  • You can only use _putchar twice in your code
julien@ubuntu:~/0x02$ cat 1-main.c
#include "holberton.h"

/**
 * main - check the code for ALX School students.
 *
 * Return: Always 0.
 */
int main(void)
{
    print_alphabet();
    return (0);
}
julien@ubuntu:~/0x02$ gcc -Wall -pedantic -Werror -Wextra -std=gnu89 _putchar.c 1-main.c 1-alphabet.c -o 1-alphabet
julien@ubuntu:~/0x02$ ./1-alphabet
abcdefghijklmnopqrstuvwxyz
julien@ubuntu:~/0x02$

Repo:

  • GitHub repository: alx-low_level_programming
  • Directory: 0x02-functions_nested_loops
  • File: 1-alphabet.c

 Done? Help Get a sandbox

2. 10 x alphabet

mandatory

Write a function that prints 10 times the alphabet, in lowercase, followed by a new line.

  • Prototype: void print_alphabet_x10(void);
  • You can only use _putchar twice in your code
julien@ubuntu:~/0x02$ cat 2-main.c
#include "holberton.h"

/**
 * main - check the code for ALX School students.
 *
 * Return: Always 0.
 */
int main(void)
{
    print_alphabet_x10();
    return (0);
}
julien@ubuntu:~/0x02$ gcc -Wall -pedantic -Werror -Wextra -std=gnu89 _putchar.c 2-main.c 2-print_alphabet_x10.c -o 2-alphabet_x10
julien@ubuntu:~/0x02$ ./2-alphabet_x10
abcdefghijklmnopqrstuvwxyz
abcdefghijklmnopqrstuvwxyz
abcdefghijklmnopqrstuvwxyz
abcdefghijklmnopqrstuvwxyz
abcdefghijklmnopqrstuvwxyz
abcdefghijklmnopqrstuvwxyz
abcdefghijklmnopqrstuvwxyz
abcdefghijklmnopqrstuvwxyz
abcdefghijklmnopqrstuvwxyz
abcdefghijklmnopqrstuvwxyz
julien@ubuntu:~/0x02$

Repo:

  • GitHub repository: alx-low_level_programming
  • Directory: 0x02-functions_nested_loops
  • File: 2-print_alphabet_x10.c

 Done? Help Get a sandbox

3. islower

mandatory

Write a function that checks for lowercase character.

  • Prototype: int _islower(int c);
  • Returns 1 if c is lowercase
  • Returns 0 otherwise

FYI: The standard library provides a similar function: islower. Run man islower to learn more.

julien@ubuntu:~/0x02$ cat 3-main.c
#include "holberton.h"

/**
 * main - check the code for ALX School students.
 *
 * Return: Always 0.
 */
int main(void)
{
    int r;

    r = _islower('H');
    _putchar(r + '0');
    r = _islower('o');
    _putchar(r + '0');
    r = _islower(108);
    _putchar(r + '0');
    _putchar('\n');
    return (0);
}
julien@ubuntu:~/0x02$ gcc -Wall -pedantic -Werror -Wextra -std=gnu89 _putchar.c 3-main.c 3-islower.c -o 3-islower
julien@ubuntu:~/0x02$ ./3-islower
011
julien@ubuntu:~/0x02$

Repo:

  • GitHub repository: alx-low_level_programming
  • Directory: 0x02-functions_nested_loops
  • File: 3-islower.c

 Done? Help Get a sandbox

4. isalpha

mandatory

Write a function that checks for alphabetic character.

  • Prototype: int _isalpha(int c);
  • Returns 1 if c is a letter, lowercase or uppercase
  • Returns 0 otherwise

FYI: The standard library provides a similar function: isalpha. Run man isalpha to learn more.

julien@ubuntu:~/0x02$ cat 4-main.c
#include "holberton.h"

/**
 * main - check the code for ALX School students.
 *
 * Return: Always 0.
 */
int main(void)
{
    int r;

    r = _isalpha('H');
    _putchar(r + '0');
    r = _isalpha('o');
    _putchar(r + '0');
    r = _isalpha(108);
    _putchar(r + '0');
    r = _isalpha(';');
    _putchar(r + '0');
    _putchar('\n');
    return (0);
}
julien@ubuntu:~/0x02$ gcc -Wall -pedantic -Werror -Wextra -std=gnu89 _putchar.c 4-main.c 4-isalpha.c -o 4-isalpha
julien@ubuntu:~/0x02$ ./4-isalpha
1110
julien@ubuntu:~/0x02$

Repo:

  • GitHub repository: alx-low_level_programming
  • Directory: 0x02-functions_nested_loops
  • File: 4-isalpha.c

 Done? Help Get a sandbox

5. Sign

mandatory

Write a function that prints the sign of a number.

  • Prototype: int print_sign(int n);
  • Returns 1 and prints + if n is greater than zero
  • Returns 0 and prints 0 if n is zero
  • Returns -1 and prints - if n is less than zero
julien@ubuntu:~/0x02$ cat 5-main.c
#include "holberton.h"

/**
 * main - check the code for ALX School students.
 *
 * Return: Always 0.
 */
int main(void)
{
    int r;

    r = print_sign(98);
    _putchar(',');
    _putchar(' ');
    _putchar(r + '0');
    _putchar('\n');
    r = print_sign(0);
    _putchar(',');
    _putchar(' ');
    _putchar(r + '0');
    _putchar('\n');
    r = print_sign(0xff);
    _putchar(',');
    _putchar(' ');
    _putchar(r + '0');
    _putchar('\n');
    r = print_sign(-1);
    _putchar(',');
    _putchar(' ');
    _putchar(r + '0');
    _putchar('\n');
    return (0);
}
julien@ubuntu:~/0x02$ gcc -Wall -pedantic -Werror -Wextra -std=gnu89 _putchar.c 5-main.c 5-sign.c -o 5-sign
julien@ubuntu:~/0x02$ ./5-sign
+, 1
0, 0
+, 1
-, /
julien@ubuntu:~/0x02$

Repo:

  • GitHub repository: alx-low_level_programming
  • Directory: 0x02-functions_nested_loops
  • File: 5-sign.c

 Done? Help Get a sandbox

6. There is no such thing as absolute value in this world. You can only estimate what a thing is worth to you

mandatory

Write a function that computes the absolute value of an integer.

  • Prototype: int _abs(int);

FYI: The standard library provides a similar function: abs. Run man abs to learn more.

julien@ubuntu:~/0x02$ cat 6-main.c
#include "holberton.h"
#include <stdio.h>

/**
 * main - check the code for ALX School students.
 *
 * Return: Always 0.
 */
int main(void)
{
    int r;

    r = _abs(-1);
    printf("%d\n", r);
    r = _abs(0);
    printf("%d\n", r);
    r = _abs(1);
    printf("%d\n", r);
    r = _abs(-98);
    printf("%d\n", r);
    return (0);
}
julien@ubuntu:~/0x02$ gcc -Wall -pedantic -Werror -Wextra -std=gnu89 _putchar.c 6-main.c 6-abs.c -o 6-abs
julien@ubuntu:~/0x02$ ./6-abs
1
0
1
98
julien@ubuntu:~/0x02$

Repo:

  • GitHub repository: alx-low_level_programming
  • Directory: 0x02-functions_nested_loops
  • File: 6-abs.c

 Done? Help Get a sandbox

7. There are only 3 colors, 10 digits, and 7 notes; it's what we do with them that's important

mandatory

Write a function that prints the last digit of a number.

  • Prototype: int print_last_digit(int);
  • Returns the value of the last digit
julien@ubuntu:~/0x02$ cat 7-main.c
#include "holberton.h"

/**
 * main - check the code for ALX School students.
 *
 * Return: Always 0.
 */
int main(void)
{
    int r;

    print_last_digit(98);
    print_last_digit(0);
    r = print_last_digit(-1024);
    _putchar('0' + r);
    _putchar('\n');
    return (0);
}
julien@ubuntu:~/0x02$ gcc -Wall -pedantic -Werror -Wextra -std=gnu89 _putchar.c 7-main.c 7-print_last_digit.c -o 7-last_digit
julien@ubuntu:~/0x02$ ./7-last_digit
8044
julien@ubuntu:~/0x02$

Repo:

  • GitHub repository: alx-low_level_programming
  • Directory: 0x02-functions_nested_loops
  • File: 7-print_last_digit.c

 Done? Help Get a sandbox

8. I'm federal agent Jack Bauer, and today is the longest day of my life

mandatory

Write a function that prints every minute of the day of Jack Bauer, starting from 00:00 to 23:59.

  • Prototype: void jack_bauer(void);
  • You can listen to this soundtrack while coding :)
julien@ubuntu:~/0x02$ cat 8-main.c
#include "holberton.h"

/**
 * main - check the code for ALX School students.
 *
 * Return: Always 0.
 */
int main(void)
{
    jack_bauer();
    return (0);
}
julien@ubuntu:~/0x02$ gcc -Wall -pedantic -Werror -Wextra -std=gnu89 _putchar.c 8-main.c 8-24_hours.c -o 8-24
julien@ubuntu:~/0x02$ ./8-24 | head
00:00
00:01
00:02
00:03
00:04
00:05
00:06
00:07
00:08
00:09
julien@ubuntu:~/0x02$ ./8-24 | tail
23:50
23:51
23:52
23:53
23:54
23:55
23:56
23:57
23:58
23:59
julien@ubuntu:~/0x02$ ./8-24 | wc -l
1440
julien@ubuntu:~/0x02$

Repo:

  • GitHub repository: alx-low_level_programming
  • Directory: 0x02-functions_nested_loops
  • File: 8-24_hours.c

 Done? Help Get a sandbox

9. Learn your times table

mandatory

Write a function that prints the 9 times table, starting with 0.

  • Prototype: void times_table(void);
  • Format: see example
julien@ubuntu:~/0x02$ cat 9-main.c
#include "holberton.h"

/**
 * main - check the code for ALX School students.
 *
 * Return: Always 0.
 */
int main(void)
{
    times_table();
    return (0);
}
julien@ubuntu:~/c/curriculum_by_julien/alx-low_level_programming/0x02$ gcc -Wall -pedantic -Werror -Wextra -std=gnu89 _putchar.c 9-main.c 9-times_table.c -o 9-times_table
ulien@ubuntu:~/0x02$ ./9-times_table | cat -e
0,  0,  0,  0,  0,  0,  0,  0,  0,  0$
0,  1,  2,  3,  4,  5,  6,  7,  8,  9$
0,  2,  4,  6,  8, 10, 12, 14, 16, 18$
0,  3,  6,  9, 12, 15, 18, 21, 24, 27$
0,  4,  8, 12, 16, 20, 24, 28, 32, 36$
0,  5, 10, 15, 20, 25, 30, 35, 40, 45$
0,  6, 12, 18, 24, 30, 36, 42, 48, 54$
0,  7, 14, 21, 28, 35, 42, 49, 56, 63$
0,  8, 16, 24, 32, 40, 48, 56, 64, 72$
0,  9, 18, 27, 36, 45, 54, 63, 72, 81$
julien@ubuntu:~/0x02$ ./9-times_table | tr ' ' . | cat -e
0,..0,..0,..0,..0,..0,..0,..0,..0,..0$
0,..1,..2,..3,..4,..5,..6,..7,..8,..9$
0,..2,..4,..6,..8,.10,.12,.14,.16,.18$
0,..3,..6,..9,.12,.15,.18,.21,.24,.27$
0,..4,..8,.12,.16,.20,.24,.28,.32,.36$
0,..5,.10,.15,.20,.25,.30,.35,.40,.45$
0,..6,.12,.18,.24,.30,.36,.42,.48,.54$
0,..7,.14,.21,.28,.35,.42,.49,.56,.63$
0,..8,.16,.24,.32,.40,.48,.56,.64,.72$
0,..9,.18,.27,.36,.45,.54,.63,.72,.81$
julien@ubuntu:~/0x02$

Repo:

  • GitHub repository: alx-low_level_programming
  • Directory: 0x02-functions_nested_loops
  • File: 9-times_table.c

 Done? Help Get a sandbox

10. a + b

mandatory

Write a function that adds two integers and returns the result.

  • Prototype: int add(int, int);
julien@ubuntu:~/$ cat 10-main.c
#include "holberton.h"
#include <stdio.h>

/**
 * main - check the code for ALX School students.
 *
 * Return: Always 0.
 */
int main(void)
{
    int n;

    n = add(89, 9);
    printf("%d\n", n);
    return (0);
}
julien@ubuntu:~/0x02$ gcc -Wall -pedantic -Werror -Wextra -std=gnu89 _putchar.c 10-main.c 10-add.c -o 10-add
julien@ubuntu:~/0x02$ ./10-add
98
julien@ubuntu:~/0x02$

Repo:

  • GitHub repository: alx-low_level_programming
  • Directory: 0x02-functions_nested_loops
  • File: 10-add.c

 Done? Help Get a sandbox

11. Holberton School, 98 Battery Street, the OG

mandatory

Write a function that prints all natural numbers from n to 98, followed by a new line.

  • Prototype: void print_to_98(int n);
  • Numbers must be separated by a comma, followed by a space
  • Numbers should be printed in order
  • The first printed number should be the number passed to your function
  • The last printed number should be 98
  • You are allowed to use the standard library
julien@ubuntu:~/0x02$ cat 11-main.c
#include "holberton.h"

/**
 * main - check the code for ALX School students.
 *
 * Return: Always 0.
 */
int main(void)
{
    print_to_98(0);
    print_to_98(98);
    print_to_98(111);
    print_to_98(81);
    print_to_98(-10);
    return (0);
}
julien@ubuntu:~/0x02$ gcc -Wall -pedantic -Werror -Wextra -std=gnu89 _putchar.c 11-main.c 11-print_to_98.c -o 11-98
julien@ubuntu:~/0x02$ ./11-98
0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71, 72, 73, 74, 75, 76, 77, 78, 79, 80, 81, 82, 83, 84, 85, 86, 87, 88, 89, 90, 91, 92, 93, 94, 95, 96, 97, 98
98
111, 110, 109, 108, 107, 106, 105, 104, 103, 102, 101, 100, 99, 98
81, 82, 83, 84, 85, 86, 87, 88, 89, 90, 91, 92, 93, 94, 95, 96, 97, 98
-10, -9, -8, -7, -6, -5, -4, -3, -2, -1, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71, 72, 73, 74, 75, 76, 77, 78, 79, 80, 81, 82, 83, 84, 85, 86, 87, 88, 89, 90, 91, 92, 93, 94, 95, 96, 97, 98
julien@ubuntu:~/0x02$

Repo:

  • GitHub repository: alx-low_level_programming
  • Directory: 0x02-functions_nested_loops
  • File: 11-print_to_98.c

 Done? Help Get a sandbox

12. The World looks like a multiplication-table, or a mathematical equation, which, turn it how you will, balances itself

#advanced

Write a function that prints the n times table, starting with 0.

  • Prototype: void print_times_table(int n);
  • If n is greater than 15 or less than 0 the function should not print anything
  • Format: see example
julien@ubuntu:~/0x02$ cat 100-main.c
#include "holberton.h"

/**
 * main - check the code for ALX School students.
 *
 * Return: Always 0.
 */
int main(void)
{
    print_times_table(3);
    _putchar('\n');
    print_times_table(5);
    _putchar('\n');
    print_times_table(98);
    _putchar('\n');
    print_times_table(12);
    return (0);
}
julien@ubuntu:~/0x02$ gcc -Wall -pedantic -Werror -Wextra -std=gnu89 _putchar.c 100-main.c 100-times_table.c -o 100-times_table
julien@ubuntu:~/0x02$ ./100-times_table
0,   0,   0,   0
0,   1,   2,   3
0,   2,   4,   6
0,   3,   6,   9

0,   0,   0,   0,   0,   0
0,   1,   2,   3,   4,   5
0,   2,   4,   6,   8,  10
0,   3,   6,   9,  12,  15
0,   4,   8,  12,  16,  20
0,   5,  10,  15,  20,  25

0,   0,   0,   0,   0,   0,   0,   0,   0,   0,   0,   0,   0
0,   1,   2,   3,   4,   5,   6,   7,   8,   9,  10,  11,  12
0,   2,   4,   6,   8,  10,  12,  14,  16,  18,  20,  22,  24
0,   3,   6,   9,  12,  15,  18,  21,  24,  27,  30,  33,  36
0,   4,   8,  12,  16,  20,  24,  28,  32,  36,  40,  44,  48
0,   5,  10,  15,  20,  25,  30,  35,  40,  45,  50,  55,  60
0,   6,  12,  18,  24,  30,  36,  42,  48,  54,  60,  66,  72
0,   7,  14,  21,  28,  35,  42,  49,  56,  63,  70,  77,  84
0,   8,  16,  24,  32,  40,  48,  56,  64,  72,  80,  88,  96
0,   9,  18,  27,  36,  45,  54,  63,  72,  81,  90,  99, 108
0,  10,  20,  30,  40,  50,  60,  70,  80,  90, 100, 110, 120
0,  11,  22,  33,  44,  55,  66,  77,  88,  99, 110, 121, 132
0,  12,  24,  36,  48,  60,  72,  84,  96, 108, 120, 132, 144
julien@ubuntu:~/0x02$ ./100-times_table | tr ' ' . | cat -e
0,...0,...0,...0$
0,...1,...2,...3$
0,...2,...4,...6$
0,...3,...6,...9$
$
0,...0,...0,...0,...0,...0$
0,...1,...2,...3,...4,...5$
0,...2,...4,...6,...8,..10$
0,...3,...6,...9,..12,..15$
0,...4,...8,..12,..16,..20$
0,...5,..10,..15,..20,..25$
$
$
0,...0,...0,...0,...0,...0,...0,...0,...0,...0,...0,...0,...0$
0,...1,...2,...3,...4,...5,...6,...7,...8,...9,..10,..11,..12$
0,...2,...4,...6,...8,..10,..12,..14,..16,..18,..20,..22,..24$
0,...3,...6,...9,..12,..15,..18,..21,..24,..27,..30,..33,..36$
0,...4,...8,..12,..16,..20,..24,..28,..32,..36,..40,..44,..48$
0,...5,..10,..15,..20,..25,..30,..35,..40,..45,..50,..55,..60$
0,...6,..12,..18,..24,..30,..36,..42,..48,..54,..60,..66,..72$
0,...7,..14,..21,..28,..35,..42,..49,..56,..63,..70,..77,..84$
0,...8,..16,..24,..32,..40,..48,..56,..64,..72,..80,..88,..96$
0,...9,..18,..27,..36,..45,..54,..63,..72,..81,..90,..99,.108$
0,..10,..20,..30,..40,..50,..60,..70,..80,..90,.100,.110,.120$
0,..11,..22,..33,..44,..55,..66,..77,..88,..99,.110,.121,.132$
0,..12,..24,..36,..48,..60,..72,..84,..96,.108,.120,.132,.144$
julien@ubuntu:~/0x02$

Repo:

  • GitHub repository: alx-low_level_programming
  • Directory: 0x02-functions_nested_loops
  • File: 100-times_table.c

 Done? Help Get a sandbox

13. Nature made the natural numbers; All else is the work of women

#advanced

If we list all the natural numbers below 10 that are multiples of 3 or 5, we get 3, 5, 6 and 9. The sum of these multiples is 23. Write a program that computes and prints the sum of all the multiples of 3 or 5 below 1024 (excluded), followed by a new line.

  • You are allowed to use the standard library

Repo:

  • GitHub repository: alx-low_level_programming
  • Directory: 0x02-functions_nested_loops
  • File: 101-natural.c

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14. In computer class, the first assignment was to write a program to print the first 100 Fibonacci numbers. Instead, I wrote a program that would steal passwords of students. My teacher gave me an A

#advanced

Write a program that prints the first 50 Fibonacci numbers, starting with 1 and 2, followed by a new line.

  • The numbers must be separated by comma, followed by a space , 
  • You are allowed to use the standard library

Repo:

  • GitHub repository: alx-low_level_programming
  • Directory: 0x02-functions_nested_loops
  • File: 102-fibonacci.c

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15. Even Liber Abbaci

#advanced

Each new term in the Fibonacci sequence is generated by adding the previous two terms. By starting with 1 and 2, the first 10 terms will be: 1, 2, 3, 5, 8, 13, 21, 34, 55, 89. By considering the terms in the Fibonacci sequence whose values do not exceed 4,000,000, write a program that finds and prints the sum of the even-valued terms, followed by a new line.

  • You are allowed to use the standard library

Repo:

  • GitHub repository: alx-low_level_programming
  • Directory: 0x02-functions_nested_loops
  • File: 103-fibonacci.c

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16. In computer class, the first assignment was to write a program to print the first 100 Fibonacci numbers. Instead, I wrote a program that would steal passwords of students. My teacher gave me an A+

#advanced

Write a program that finds and prints the first 98 Fibonacci numbers, starting with 1 and 2, followed by a new line.

  • The numbers should be separated by comma, followed by a space ,
  • You are allowed to use the standard library
  • You are not allowed to use any other library (You can't use GMP etc...)
  • You are not allowed to use long long, malloc, pointers, arrays/tables, or structures
  • You are not allowed to hard code any Fibonacci number (except for 1 and 2)

Repo:

  • GitHub repository: alx-low_level_programming
  • Directory: 0x02-functions_nested_loops
  • File: 104-fibonacci.c