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

Resources

Learning Objectives

Tasks

Learning Objectives - Answers

- What are the arithmetic operators and how to use them

Arithmetic operators are operators used in mathematical expressions in programming. Here are the commonly used arithmetic operators in C++:

Operator Operation
+ Addition
- Subtraction
* Multiplication
/ Division
% Modulo (Remainder)

Example of arithmetic operators in C:

int a = 5, b = 3, c;
c = a + b; // Addition
c = a - b; // Subtraction
c = a * b; // Multiplication
c = a / b; // Division
c = a % b; // Modulo

Note that in C++, integer division truncates the result to the nearest integer. For example, 5/3 evaluates to 1, not 1.6667. If you want a floating-point result, you can use a floating-point type such as float or double.

- What are the logical operators (sometimes called boolean operators) and how to use them

Logical operators in C are used to evaluate conditions and return true or false (boolean) values. There are three logical operators in C:

  • && (logical AND): Returns true if both operands are true, otherwise returns false.
  • || (logical OR): Returns true if either operand is true, otherwise returns false.
  • ! (logical NOT): Returns true if the operand is false, otherwise returns false.

Example:

#include <stdio.h>
#include <stdbool.h>

int main() {
    bool a = true;
    bool b = false;

    if (a && b) {
        printf("Both a and b are true.\n");
    } else if (a || b) {
        printf("Either a or b is true.\n");
    } else {
        printf("Neither a nor b is true.\n");
    }

    if (!b) {
        printf("b is false.\n");
    }

    return 0;
}

- What the relational operators and how to use them

Relational operators are used to compare two values and return a boolean value (true or false). The relational operators in C are:

  • == : equal to
  • != : not equal to
  • < : less than
  • > : greater than
  • <= : less than or equal to
  • >= : greater than or equal to

Here is an example of how to use them in C:

#include <stdio.h>

int main() {
    int a = 5;
    int b = 10;

    if (a == b) {
        printf("a is equal to b\n");
    } else if (a != b) {
        printf("a is not equal to b\n");
    }

    if (a < b) {
        printf("a is less than b\n");
    }

    if (b > a) {
        printf("b is greater than a\n");
    }

    if (a <= b) {
        printf("a is less than or equal to b\n");
    }

    if (b >= a) {
        printf("b is greater than or equal to a\n");
    }

    return 0;
}

- What values are considered TRUE and FALSE in C

In C, the value 0 is considered FALSE, while any other non-zero value is considered TRUE. For example, the following code will print "TRUE" because the value of a is non-zero:

#include <stdio.h>

int main() {
    int a = 5;

    if (a) {
        printf("TRUE\n");
    } else {
        printf("FALSE\n");
    }

    return 0;
}

In C, any non-zero value is considered TRUE and a zero value is considered FALSE. This is because C uses a concept called "truthiness", where any value that is not explicitly false is considered true. In practical terms, this means that any condition that evaluates to a non-zero value will be considered true, while a condition that evaluates to zero will be considered false. This is a simple and intuitive approach that allows for concise and readable code.

- What are the boolean operators and how to use them

Boolean operators are operators that are used to evaluate a condition as either true or false. In C, the boolean operators are:

  • && (logical AND): returns true if both operands are true, false otherwise.
  • || (logical OR): returns true if at least one operand is true, false otherwise.
  • ! (logical NOT): returns true if the operand is false, false if the operand is true.

Here's an example of using boolean operators in C:

int x = 5, y = 10;
if (x < y && y < 20) {
    printf("x is less than y and y is less than 20\n");
}
if (x > 3 || y > 15) {
    printf("either x is greater than 3 or y is greater than 15 (or both)\n");
}
if (!(x == 7)) {
    printf("x is not equal to 7\n");
}

- How to use the if, if ... else statements

The if statement is used to check a condition and execute the code inside the block if the condition is true. Here's an example:

int x = 10;

if (x > 5) {
    printf("x is greater than 5\n");
}

In this example, the condition x > 5 is true, so the code inside the if block is executed and "x is greater than 5" is printed to the console.

The if ... else statement is used to check a condition and execute one block of code if the condition is true and another block of code if the condition is false. Here's an example:

int x = 10;

if (x > 5) {
    printf("x is greater than 5\n");
} else {
    printf("x is less than or equal to 5\n");
}

In this example, the condition x > 5 is true, so the code inside the first block is executed and "x is greater than 5" is printed to the console. If the condition had been false, the code inside the second block would have been executed instead and "x is less than or equal to 5" would have been printed.

- How to use comments

In C programming language, we can use two types of comments:

  1. Single-line comments: This is used to comment on a single line of code. The compiler will ignore everything after the // until the end of the line.
// This is a single-line comment
int x = 5; // This is also a single-line comment
  1. Multi-line comments: This is used to comment on multiple lines of code. The compiler will ignore everything between /* and */.
/* This is a multi-line
   comment */
int x = 5; /* This is also a
               multi-line comment */

It is recommended to use comments in your code to make it more readable and understandable.

- How to declare variables of types char, int, unsigned int

To declare variables of types char, int, and unsigned int, you can use the following syntax:

char myChar = 'a';
int myInt = 42;
unsigned int myUInt = 12345;

- How to assign values to variables

To assign a value to a variable in C, you need to use the assignment operator =. The general syntax is:

variable = value;

Here's an example of how to declare and assign values to variables of types char, int, unsigned int:

#include <stdio.h>

int main() {
    char c = 'a';
    int i = 42;
    unsigned int ui = 100;

    printf("c = %c\n", c);
    printf("i = %d\n", i);
    printf("ui = %u\n", ui);

    return 0;
}

The output of this program is:

c = a
i = 42
ui = 100

- How to print the values of variables of type char, int, unsigned int with printf

In C programming language, printfis a function that is used to print the formatted output to the standard output (stdout) stream. It takes a format string as the first argument, which specifies how the output should be formatted, followed by the values of the variables that should be printed. The format string is made up of literal text and format specifiers. The format specifiers are used to specify the type and format of the corresponding argument.

To print the value of a variable of type char, the %c format specifier is used. For example:

char ch = 'a';
printf("The value of ch is %c\n", ch);

To print the value of a variable of type int, the %d or %i format specifier is used. For example:

int num = 42;
printf("The value of num is %d\n", num);

To print the value of a variable of type unsigned int, the %u format specifier is used. For example:

unsigned int num = 42;
printf("The value of num is %u\n", num);

It is important to use the correct format specifier for the type of the variable being printed. Using the wrong format specifier can result in undefined behavior, such as printing garbage values or crashing the program.

- How to use the while loop

The while loop is used to repeatedly execute a block of code while a certain condition is true. The syntax of the while loop in C is as follows:

while (condition) {
   // code to be executed while the condition is true
}

The condition is an expression that is evaluated at the beginning of each iteration of the loop. If the condition is true, the block of code inside the loop is executed. This continues until the condition becomes false.

Here is an example of using a while loop to print the numbers from 1 to 10:

int i = 1;
while (i <= 10) {
    printf("%d ", i);
    i++;
}

In this example, the variable i is initialized to 1 before the loop. The condition i <= 10 is true for the first 10 iterations of the loop, so the block of code inside the loop is executed 10 times. The value of i is printed on each iteration, and then incremented by 1 using the i++ statement. The loop continues until i becomes greater than 10, at which point the condition becomes false and the loop terminates.

- How to use variables with the while loop

To use variables with the while loop in C, you need to declare the variable before the loop and update it inside the loop. Here's an example:

#include <stdio.h>

int main() {
    int i = 0; // Declare and initialize the variable

    while (i < 10) { // Loop condition
        printf("%d ", i); // Print the variable
        i++; // Update the variable
    }

    return 0;
}

- How to print variables using printf

To print variables using printf, you need to use format specifiers to specify the type of the variable being printed. Here are the format specifiers for the most common types of variables:

Type Format Specifier
%d for int
%u for unsigned int
%c for char
%s for string (array of characters)
%f for float
%lf for double

Here's an example of how to print the value of a variable of type int and float using printf:

int x = 10;
float y = 3.14;
printf("The value of x is: %d and the value of y is: %f\n", x, y);

- What is the ASCII character set

The ASCII (American Standard Code for Information Interchange) character set is a character encoding standard for electronic communication. It represents 128 characters including uppercase and lowercase letters, numbers, punctuation marks, and control characters.

Here are some examples of ASCII characters and their decimal values:

  • Decimal 65: A
  • Decimal 97: a
  • Decimal 48: 0
  • Decimal 33: !
  • Decimal 32: Space character
  • man ascii for more information The ASCII character set is widely used in computer systems and programming languages.

- What are the purpose of the gcc flags -m32 and -m64

The -m32 and -m64 flags are used to specify the target architecture for the code being compiled with gcc.

The -m32 flag tells gcc to generate code for a 32-bit environment, while the -m64 flag tells it to generate code for a 64-bit environment.

The purpose of these flags is to control the size and layout of data types, pointers, and memory addressing in the compiled code. They are useful when compiling code for different architectures or when compiling code that must interact with code compiled for a different architecture.

For example, if you are compiling code for a 32-bit system, you would use the -m32 flag to ensure that the code is compiled with the correct memory layout and addressing scheme for that architecture. Similarly, if you are compiling code for a 64-bit system, you would use the -m64 flag to ensure that the code is compiled for that architecture.

Examples:

To compile a C program for a 32-bit architecture:

gcc -m32 -o program program.c

To compile a C program for a 64-bit architecture:

gcc -m64 -o program program.c

Tasks

0. Positive anything is better than negative nothing

Task 0

positive or negative

Compiled with: gcc -Wall -pedantic -Werror -Wextra -std=gnu89 0-positive_or_negative.c -o 0-positive_or_negative

Output:

$ ./0-positive_or_negative
-1 is negative
$ ./0-positive_or_negative
0 is zero
$ ./0-positive_or_negative
1 is positive
1. The last digit

Task 1

last digit

Compile this way: gcc -Wall -pedantic -Werror -Wextra -std=gnu89 1-last_digit.c -o 1-last_digit

Output:

$ ./1-last_digit
Last digit of 98 is 8 and is greater than 5
$ ./1-last_digit
Last digit of 0 is 0 and is 0
$ ./1-last_digit
Last digit of 402 is 2 and is less than 6 and not 0
2. I sometimes suffer from insomnia. And when I can't fall asleep, I play what I call the alphabet game

Task 2

alphabet

Compile this way: gcc -Wall -pedantic -Werror -Wextra -std=gnu89 2-print_alphabet.c -o 2-print_alphabet

Output:

$ ./2-print_alphabet
abcdefghijklmnopqrstuvwxyz
3. alphABET
alphabets

Compile this way: gcc -Wall -pedantic -Werror -Wextra -std=gnu89 3-print_alphabets.c -o 3-print_alphabets

Output:

$ ./3-print_alphabets
abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ
4. When I was having that alphabet soup, I never thought that it would pay off

Task 4

alphabets

Compile this way: gcc -Wall -pedantic -Werror -Wextra -std=gnu89 4-print_alphabt.c -o 4-print_alphabt Output:

$ ./4-print_alphabt
abcdfghijklmnoprstuvwxyz
$ ./4-print_alphabt | grep [eq]
$
5. Numbers

Task 5

numbers

Compile this way: gcc -Wall -pedantic -Werror -Wextra -std=gnu89 5-print_numbers.c -o 5-print_numbers

Output:

$ ./5-print_numbers
0123456789
6. Numberz

Task 6

numberz
  • This ASCII table will help you understand my solution.
    • For this you need to understand that putchar holds the decimal representation of the variable.
    • So we add 0 == 48 48 is the decimal value to our single digit integer to convert it into its character representation.
    • Better explanation here

Compile this way: gcc -Wall -pedantic -Werror -Wextra -std=gnu89 6-print_numberz.c -o 6-print_numberz

Output:

$ ./6-print_numberz
0123456789
7. Smile in the mirror

Task 7

tebahpla

Compile this way: gcc -Wall -pedantic -Werror -Wextra -std=gnu89 7-print_tebahpla.c -o 7-print_tebahpla

Output:

$ ./7-print_tebahpla
zyxwvutsrqponmlkjihgfedcba
8. Hexadecimal

Task 8

base16

Compile this way: gcc -Wall -pedantic -Werror -Wextra -std=gnu89 8-print_base16.c -o 8-print_base16

Output:

$ ./8-print_base16
0123456789abcdef
9. Patience, persistence and perspiration make an unbeatable combination for success

Task 9

comb

Compile this way: gcc -Wall -pedantic -Werror -Wextra -std=gnu89 9-print_comb.c -o 9-print_comb

Output:

$ ./9-print_comb | cat -e
0, 1, 2, 3, 4, 5, 6, 7, 8, 9$
10. Inventing is a combination of brains and materials. The more brains you use, the less material you need

Task 10

comb3

Compile this way: gcc -Wall -pedantic -Werror -Wextra -std=gnu89 100-print_comb3.c -o 100-print_comb3

Output:

$ ./100-print_comb3
01, 02, 03, 04, 05, 06, 07, 08, 09, 12, 13, 14, 15, 16, 17, 18, 19, 23, 24, 25, 26, 27, 28, 29, 34, 35, 36, 37, 38, 39, 45, 46, 47, 48, 49, 56, 57, 58, 59, 67, 68, 69, 78, 79, 89
11. The success combination in business is: Do what you do better... and: do more of what you do...

Task 11

comb4

Compile this way: gcc -Wall -pedantic -Werror -Wextra -std=gnu89 101-print_comb4.c -o 101-print_comb4

Output:

$ ./101-print_comb4
012, 013, 014, 015, 016, 017, 018, 019, 023, 024, 025, 026, 027, 028, 029, 034, 035, 036, 037, 038, 039, 045, 046, 047, 048, 049, 056, 057, 058, 059, 067, 068, 069, 078, 079, 089, 123, 124, 125, 126, 127, 128, 129, 134, 135, 136, 137, 138, 139, 145, 146, 147, 148, 149, 156, 157, 158, 159, 167, 168, 169, 178, 179, 189, 234, 235, 236, 237, 238, 239, 245, 246, 247, 248, 249, 256, 257, 258, 259, 267, 268, 269, 278, 279, 289, 345, 346, 347, 348, 349, 356, 357, 358, 359, 367, 368, 369, 378, 379, 389, 456, 457, 458, 459, 467, 468, 469, 478, 479, 489, 567, 568, 569, 578, 579, 589, 678, 679, 689, 789
12. Software is eating the World

Task 12

comb5

Compile this way: gcc -Wall -pedantic -Werror -Wextra -std=gnu89 102-print_comb5.c -o 102-print_comb5

Output:

$ ./102-print_comb5
00 01, 00 02, 00 03, 00 04, 00 05, 00 06, 00 07, 00 08, 00 09, 00 10, 00 11, [...] 40 91, 40 92, 40 93, 40 94, 40 95, 40 96, 40 97, 40 98, 40 99, 41 42, 41 43, 41 44, 41 45, 41 46, 41 47, 41 48, 41 49, 41 50, 41 51, 41 52, 41 53 [...] 93 95, 93 96, 93 97, 93 98, 93 99, 94 95, 94 96, 94 97, 94 98, 94 99, 95 96, 95 97, 95 98, 95 99, 96 97, 96 98, 96 99, 97 98, 97 99, 98 99

Notes

?: operator

The ?: operator is called the ternary operator. It is a shortcut for an if statement. It is used to evaluate a condition and return a value based on the result of the condition. The syntax is as follows:

condition ? expression1 : expression2;
  • The condition is a boolean expression that is evaluated first.
  • If the condition is true, the expression1 is evaluated and returned.
  • If the condition is false, the expression2 is evaluated and returned.

Example

int x = 5;
int y = 10;
int z = x < y ? x : y;

In this example, the condition x < y is true, so the value of z is x, which is 5. The ternary operator can be used to simplify if statements. For example, the following if statement:

if (x < y)
{
    z = x;
}
else
{
    z = y;
}

can be rewritten as:

z = x < y ? x : y;