SE-Foundation Help

0x02. C - Functions, nested loops

Resources

Nested While Loops

Learning to Program in C (Part 06)

C Programming Loops & Functions

Functions in C programming

    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

        gcc -Wall -Werror -Wextra -pedantic -std=gnu89 *.c

      • 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 -Wall -Werror -Wextra -pedantic -std=gnu89 *.c

      • 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

        #include <unistd.h> /** * _putchar - writes the character c to stdout * @c: The character to print * * Return: On success 1. * On error, -1 is returned, and errno is set appropriately. */ int _putchar(char c) { return (write(1, &c, 1)); }

      • In the following examples, the main.c files are shown as examples. You can use them to test your functions.

      • The prototypes of all your functions and the prototype of the function _putchar should be included in your header file called main.h

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

      Tasks

      0. _putchar

      0-putchar.c

      Write a program that prints _putchar, followed by a new line

      • The program should return 0

      #include <unistd.h> /** * _putchar - writes the character c to stdout * @c: The character to print * * Return: On success 1. * On error, -1 is returned, and errno is set appropriately. */ int _putchar(char c) { return (write(1, &c, 1)); }
      gcc -Wall -pedantic -Werror -Wextra -std=gnu89 _putchar.c 0-putchar.c -o 0-putchar
      ./0-putchar
      _putchar

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

      1-alphabet.c

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

      void print_alphabet(void);

      • You can only use _putchar twice in your code.

      #include <unistd.h> /** * _putchar - writes the character c to stdout * @c: The character to print * * Return: On success 1. * On error, -1 is returned, and errno is set appropriately. */ int _putchar(char c) { return (write(1, &c, 1)); }
      #include "main.h" /** * main - check the code * * Return: Always 0. */ int main(void) { print_alphabet(); return (0); }
      gcc -Wall -pedantic -Werror -Wextra -std=gnu89 _putchar.c 1-main.c 1-alphabet.c -o 1-alphabet
      ./1-alphabet
      abcdefghijklmnopqrstuvwxyz

      2. 10 x alphabet

      2-print_alphabet_x10.c

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

      void print_alphabet_x10(void);

      • You can only use _putchar twice in your code.

      #include <unistd.h> /** * _putchar - writes the character c to stdout * @c: The character to print * * Return: On success 1. * On error, -1 is returned, and errno is set appropriately. */ int _putchar(char c) { return (write(1, &c, 1)); }
      #include "main.h" /** * main - check the code. * * Return: Always 0. */ int main(void) { print_alphabet_x10(); return (0); }
      gcc -Wall -pedantic -Werror -Wextra -std=gnu89 _putchar.c 2-main.c 2-print_alphabet_x10.c -o 2-alphabet_x10
      ./2-alphabet_x10
      abcdefghijklmnopqrstuvwxyz abcdefghijklmnopqrstuvwxyz abcdefghijklmnopqrstuvwxyz abcdefghijklmnopqrstuvwxyz abcdefghijklmnopqrstuvwxyz abcdefghijklmnopqrstuvwxyz abcdefghijklmnopqrstuvwxyz abcdefghijklmnopqrstuvwxyz abcdefghijklmnopqrstuvwxyz abcdefghijklmnopqrstuvwxyz

      3. islower

      3-islower.c

      Write a function that checks for lowercase character.

      int _islower(int c);

      • It should:

        • Return 1 if arg c is lowercase

        • Return 0 otherwise

      #include <unistd.h> /** * _putchar - writes the character c to stdout * @c: The character to print * * Return: On success 1. * On error, -1 is returned, and errno is set appropriately. */ int _putchar(char c) { return (write(1, &c, 1)); }
      #include "main.h" /** * main - check the code. * * 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); }
      gcc -Wall -pedantic -Werror -Wextra -std=gnu89 _putchar.c 3-main.c 3-islower.c -o 3-islower
      ./3-islower
      011

      4. isalpha

      4-isalpha.c

      Write a function that checks for alphabetic character.

      int _isalpha(int c);

      • It should:

        • Return 1 if arg c is a letter, lowercase or uppercase

        • Return 0 otherwise

      • FYI: The standard library provides a similar function: isalpha. To learn more Run

        man isalpha
      #include <unistd.h> /** * _putchar - writes the character c to stdout * @c: The character to print * * Return: On success 1. * On error, -1 is returned, and errno is set appropriately. */ int _putchar(char c) { return (write(1, &c, 1)); }
      #include "main.h" /** * main - check the code. * * 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); }
      gcc -Wall -pedantic -Werror -Wextra -std=gnu89 _putchar.c 4-main.c 4-isalpha.c -o 4-isalpha
      ./4-isalpha
      1110

      5. Sign

      5-sign.c

      Write a function that prints the sign of a number.

      int print_sign(int n);

      • It should:

        • 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

      #include <unistd.h> /** * _putchar - writes the character c to stdout * @c: The character to print * * Return: On success 1. * On error, -1 is returned, and errno is set appropriately. */ int _putchar(char c) { return (write(1, &c, 1)); }
      #include "main.h" /** * main - check the code. * * 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); }
      gcc -Wall -pedantic -Werror -Wextra -std=gnu89 _putchar.c 5-main.c 5-sign.c -o 5-sign
      ./5-sign
      +, 1 0, 0 +, 1 -, /

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

      6-abs.c

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

      int _abs(int);

      • FYI: The standard library provides a similar function: abs. To learn more Run

        man abs
      #include <unistd.h> /** * _putchar - writes the character c to stdout * @c: The character to print * * Return: On success 1. * On error, -1 is returned, and errno is set appropriately. */ int _putchar(char c) { return (write(1, &c, 1)); }
      #include "main.h" #include <stdio.h> /** * main - check the code * * 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); }
      gcc -Wall -pedantic -Werror -Wextra -std=gnu89 _putchar.c 6-main.c 6-abs.c -o 6-abs
      ./6-abs
      1 0 1 98

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

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

      • int print_last_digit(int);

      • Return the value of the last digit

      julien@ubuntu:~/0x02$ cat 7-main.c #include "main.h" /** * main - check the code * * 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$

        Repository

        GitHub repository: alx-low_level_programming

        Directory: 0x02-functions_nested_loops

        File: 0-putchar.c 1-alphabet.c 2-print_alphabet_x10.c 3-islower.c 4-isalpha.c 5-sign.c 6-abs.c 7-print_last_digit.c

          Tasks

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

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

          void jack_bauer(void);

          You can listen to this soundtrack while coding :)

          julien@ubuntu:~/0x02$ cat 8-main.c #include "main.h" /** * main - check the code * * 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

          9. Learn your times table

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

          void times_table(void);

          • Format: see example

          julien@ubuntu:~/0x02$ cat 9-main.c #include "main.h" /** * main - check the code * * Return: Always 0. */ int main(void) { times_table(); return (0); } julien@ubuntu:~/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

          10. a + b

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

          int add(int, int);
          julien@ubuntu:~/$ cat 10-main.c #include "main.h" #include <stdio.h> /** * main - check the code * * 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

          11. 98 Battery Street, the OG

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

          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 "main.h" /** * main - check the code * * 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

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

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

          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 "main.h" /** * main - check the code. * * 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

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

          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 not allowed to use the standard library

          Repo:

          • GitHub repository: alx-low_level_programming

          • Directory: 0x02-functions_nested_loops

          • File: 101-natural.c

          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

          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

          15. Even Liber Abbaci

          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

          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+

          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

            Last modified: 27 September 2024
            First Day of C Programming0x03. C - Debugging