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

• By Julien Barbier

Resources

Read or watch:

• Everything you need to know to start with C.pdf (You do not have to learn everything in there yet, but make sure you read it entirely first and make sure you understand the slides: "comments", "Data types | Integer types", "Declaration", "Characters", "Arithmetic operators", "Variables assignments", "Comparisons", "Logical operators", "if, if...else", "while loops".)
• Keywords and identifiers
• integers
• Arithmetic Operators in C
• If statements in C
• if...else statement
• Relational operators
• Logical operators
• while loop in C
• While loop

man or help:

• ascii (You do not need to learn about scanf, getc, getchar, EOF, EXIT_SUCCESS, time, rand, srand, RAND_MAX, for loops, do...while loops, functions.)

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 the arithmetic operators and how to use them
• What are the logical operators (sometimes called boolean operators) and how to use them
• What the the relational operators and how to use them
• What values are considered TRUE and FALSE in C
• What are the boolean operators and how to use them
• How to use the if, if ... else statements
• How to use comments
• How to declare variables of types char, int, unsigned int
• How to assign values to variables
• How to print the values of variables of type char, int, unsigned int with printf
• How to use the while loop
• How to use variables with the while loop
• How to print variables using printf
• What is the ASCII character set
• What are the purpose of the gcc flags -m32 and -m64

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
• There should be no errors and no warnings during compilation
• You are not allowed to use system
• Your code should use the Betty style. It will be checked using betty-style.pl and betty-doc.pl

Tasks

0. Positive anything is better than negative nothing

mandatory

This program will assign a random number to the variable n each time it is executed. Complete the source code in order to print whether the number stored in the variable n is positive or negative.

• You can find the source code here
• The variable n will store a different value every time you will run this program
• You don't have to understand what rand, srand, RAND_MAX do. Please do not touch this code
• The output of the program should be:
  • The number, followed by
    • if the number is greater than 0: is positive
    • if the number is 0: is zero
    • if the number is less than 0: is negative
  • followed by a new line

julien@ubuntu:~/0x01$ gcc -Wall -pedantic -Werror -Wextra -std=gnu89 0-positive_or_negative.c -o 0-positive_or_negative
julien@ubuntu:~/0x01$ ./0-positive_or_negative
-520693284 is negative
julien@ubuntu:~/0x01$ ./0-positive_or_negative
-973398895 is negative
julien@ubuntu:~/0x01$ ./0-positive_or_negative
-199220452 is negative
julien@ubuntu:~/0x01$ ./0-positive_or_negative
561319348 is positive
julien@ubuntu:~/0x01$ ./0-positive_or_negative
561319348 is positive
julien@ubuntu:~/0x01$ ./0-positive_or_negative
266853958 is positive
julien@ubuntu:~/0x01$ ./0-positive_or_negative
-48147767 is negative
julien@ubuntu:~/0x01$ ./0-positive_or_negative
0 is zero
julien@ubuntu:~/0x01$

Repo:

• GitHub repository: alx-low_level_programming
• Directory: 0x01-variables_if_else_while
• File: 0-positive_or_negative.c

Done? Help Get a sandbox

1. The last digit

mandatory

This program will assign a random number to the variable n each time it is executed. Complete the source code in order to print the last digit of the number stored in the variable n.

• You can find the source code here
• The variable n will store a different value every time you run this program
• You don't have to understand what rand, srand, and RAND_MAX do. Please do not touch this code
• The output of the program should be:
  • The string Last digit of, followed by
  • n, followed by
  • the string is, followed by
    • if the last digit of n is greater than 5: the string and is greater than 5
    • if the last digit of n is 0: the string and is 0
    • if the last digit of n is less than 6 and not 0: the string and is less than 6 and not 0
  • followed by a new line

julien@ubuntu:~/0x01$ gcc -Wall -pedantic -Werror -Wextra -std=gnu89 1-last_digit.c -o 1-last_digit
julien@ubuntu:~/0x01$ ./1-last_digit
Last digit of 629438752 is 2 and is less than 6 and not 0
julien@ubuntu:~/0x01$ ./1-last_digit
Last digit of -748255693 is -3 and is less than 6 and not 0
julien@ubuntu:~/0x01$ ./1-last_digit
Last digit of -1052791662 is -2 and is less than 6 and not 0
julien@ubuntu:~/0x01$ ./1-last_digit
Last digit of -284805734 is -4 and is less than 6 and not 0
julien@ubuntu:~/0x01$ ./1-last_digit
Last digit of -284805734 is -4 and is less than 6 and not 0
julien@ubuntu:~/0x01$ ./1-last_digit
Last digit of 491506926 is 6 and is greater than 5
julien@ubuntu:~/0x01$ ./1-last_digit
Last digit of 954249937 is 7 and is greater than 5
julien@ubuntu:~/0x01$ ./1-last_digit
Last digit of 652334952 is 2 and is less than 6 and not 0
julien@ubuntu:~/0x01$ ./1-last_digit
Last digit of -729688197 is -7 and is less than 6 and not 0
julien@ubuntu:~/0x01$ ./1-last_digit
Last digit of -729688197 is -7 and is less than 6 and not 0
julien@ubuntu:~/0x01$ ./1-last_digit
Last digit of 45528266 is 6 and is greater than 5
julien@ubuntu:~/0x01$ ./1-last_digit
Last digit of 45528266 is 6 and is greater than 5
julien@ubuntu:~/0x01$ ./1-last_digit
Last digit of 809065140 is 0 and is 0
julien@ubuntu:~/0x01$

Repo:

• GitHub repository: alx-low_level_programming
• Directory: 0x01-variables_if_else_while
• File: 1-last_digit.c

Done? Help Get a sandbox

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

mandatory

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

• You can only use the putchar function (every other function (printf, puts, etc...) is forbidden)
• All your code should be in the main function
• You can only use putchar twice in your code

julien@ubuntu:~/0x01$ gcc -Wall -pedantic -Werror -Wextra -std=gnu89 2-print_alphabet.c -o 2-print_alphabet
julien@ubuntu:~/0x01$ ./2-print_alphabet
abcdefghijklmnopqrstuvwxyz
julien@ubuntu:~/0x01$

Repo:

• GitHub repository: alx-low_level_programming
• Directory: 0x01-variables_if_else_while
• File: 2-print_alphabet.c

Done? Help Get a sandbox

3. alphABET

mandatory

Write a program that prints the alphabet in lowercase, and then in uppercase, followed by a new line.

• You can only use the putchar function (every other function (printf, puts, etc...) is forbidden)
• All your code should be in the main function
• You can only use putchar three times in your code

julien@ubuntu:~/0x01$ gcc -Wall -pedantic -Werror -Wextra -std=gnu89 3-print_alphabets.c -o 3-print_alphabets
julien@ubuntu:~/0x01$ ./3-print_alphabets | cat -e
abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ$
julien@ubuntu:~/0x01$

Repo:

• GitHub repository: alx-low_level_programming
• Directory: 0x01-variables_if_else_while
• File: 3-print_alphabets.c

Done? Help Get a sandbox

4. When I was having that alphabet soup, I never thought that it would pay off

mandatory

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

• Print all the letters except q and e
• You can only use the putchar function (every other function (printf, puts, etc...) is forbidden)
• All your code should be in the main function
• You can only use putchar twice in your code

julien@ubuntu:~/0x01$ gcc -Wall -pedantic -Werror -Wextra -std=gnu89 4-print_alphabt.c -o 4-print_alphabt
julien@ubuntu:~/0x01$ ./4-print_alphabt
abcdfghijklmnoprstuvwxyz
julien@ubuntu:~/0x01$ ./4-print_alphabt | grep [eq]
julien@ubuntu:~/0x01$

Repo:

• GitHub repository: alx-low_level_programming
• Directory: 0x01-variables_if_else_while
• File: 4-print_alphabt.c

Done? Help Get a sandbox

5. Numbers

mandatory

Write a program that prints all single digit numbers of base 10 starting from 0, followed by a new line.

• All your code should be in the main function

julien@ubuntu:~/0x01$ gcc -Wall -pedantic -Werror -Wextra -std=gnu89 5-print_numbers.c -o 5-print_numbers
julien@ubuntu:~/0x01$ ./5-print_numbers
0123456789
julien@ubuntu:~/0x01$

Repo:

• GitHub repository: alx-low_level_programming
• Directory: 0x01-variables_if_else_while
• File: 5-print_numbers.c

Done? Help Get a sandbox

6. Numberz

mandatory

Write a program that prints all single digit numbers of base 10 starting from 0, followed by a new line.

• You are not allowed to use any variable of type char
• You can only use the putchar function (every other function (printf, puts, etc...) is forbidden)
• You can only use putchar twice in your code
• All your code should be in the main function

julien@ubuntu:~/0x01$ gcc -Wall -pedantic -Werror -Wextra -std=gnu89 6-print_numberz.c -o 6-print_numberz
julien@ubuntu:~/0x01$ ./6-print_numberz
0123456789
julien@ubuntu:~/0x01$

Repo:

• GitHub repository: alx-low_level_programming
• Directory: 0x01-variables_if_else_while
• File: 6-print_numberz.c

Done? Help Get a sandbox

7. Smile in the mirror

mandatory

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

• You can only use the putchar function (every other function (printf, puts, etc...) is forbidden)
• All your code should be in the main function
• You can only use putchar twice in your code

julien@ubuntu:~/0x01$ gcc -Wall -pedantic -Werror -Wextra -std=gnu89 7-print_tebahpla.c -o 7-print_tebahpla
julien@ubuntu:~/0x01$ ./7-print_tebahpla
zyxwvutsrqponmlkjihgfedcba
julien@ubuntu:~/0x01$

Repo:

• GitHub repository: alx-low_level_programming
• Directory: 0x01-variables_if_else_while
• File: 7-print_tebahpla.c

Done? Help Get a sandbox

8. Hexadecimal

mandatory

Write a program that prints all the numbers of base 16 in lowercase, followed by a new line.

• You can only use the putchar function (every other function (printf, puts, etc...) is forbidden)
• All your code should be in the main function
• You can only use putchar three times in your code

julien@ubuntu:~/0x01$ gcc -Wall -pedantic -Werror -Wextra -std=gnu89 8-print_base16.c -o 8-print_base16
julien@ubuntu:~/0x01$ ./8-print_base16
0123456789abcdef
julien@ubuntu:~/0x01$

Repo:

• GitHub repository: alx-low_level_programming
• Directory: 0x01-variables_if_else_while
• File: 8-print_base16.c

Done? Help Get a sandbox

9. Patience, persistence and perspiration make an unbeatable combination for success

mandatory

Write a program that prints all possible combinations of single-digit numbers.

• Numbers must be separated by ,, followed by a space
• Numbers should be printed in ascending order
• You can only use the putchar function (every other function (printf, puts, etc...) is forbidden)
• All your code should be in the main function
• You can only use putchar four times maximum in your code
• You are not allowed to use any variable of type char

julien@ubuntu:~/0x01$ gcc -Wall -pedantic -Werror -Wextra -std=gnu89 9-print_comb.c -o 9-print_comb
julien@ubuntu:~/0x01$ ./9-print_comb | cat -e
0, 1, 2, 3, 4, 5, 6, 7, 8, 9$
julien@ubuntu:~/0x01$

Repo:

• GitHub repository: alx-low_level_programming
• Directory: 0x01-variables_if_else_while
• File: 9-print_comb.c