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Loop & Switch-Case

Loop & Switch-Case

1. While Loop

A while loop is a function used to execute the same block of code repeatedly. The loop continues execution as long as the given condition evaluates to 1 (TRUE) or more. When the condition evaluates to 0 (FALSE), the loop stops and the program proceeds to the next lines of code.

Similar to an if statement, the while loop is built into the C programming language, meaning there is no need to declare or return its value explicitly.

Syntax:

while (condition) {
    // Code to be executed repeatedly
}

The condition is checked before executing the loop body:

  • If condition is TRUE, the code inside the loop is executed.
  • If condition is FALSE, the loop terminates.

Example 1: Counting from 1 to 10

#include <stdio.h>

int main() {
    int n = 1;

    while (n <= 10) {  // Loop runs while n is less than or equal to 10
        printf("%d\n", n);
        n++;  // Increment n by 1 in each iteration
    }

    return 0;
}

Output:

1
2
3
4
5
6
7
8
9
10

Infinite Loop

If the condition never changes or is always TRUE, the loop will run indefinitely.

Example 2: Infinite Loop (Press Ctrl+C to Stop)

#include <stdio.h>

int main() {
    while (1) {  // The condition is always TRUE
        printf("This loop will run forever!\n");
    }

    return 0;
}

Output (Repeats Forever):

This loop will run forever!
This loop will run forever!
This loop will run forever!
...

Using break to Exit a While Loop

The break statement can be used to exit a while loop forcefully.

Example 3: Using break to Stop the Loop

#include <stdio.h>

int main() {
    int n = 1;

    while (1) {  // Infinite loop
        printf("%d\n", n);
        if (n == 5) {
            break;  // Exit the loop when n reaches 5
        }
        n++;
    }

    return 0;
}

Output:

1
2
3
4
5

Using continue to Skip an Iteration

The continue statement is used to skip the remaining code in the loop for a specific iteration.

Example 4: Skipping a Number (Skipping 5)

#include <stdio.h>

int main() {
    int n = 0;

    while (n < 10) {
        n++;
        
        if (n == 5) {
            continue;  // Skip printing 5
        }

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

    return 0;
}

Output:

1
2
3
4
6
7
8
9
10

2. DO-WHILE LOOP

The do-while loop is similar to the while loop. The difference lies in the execution order:

  • In a while loop, the condition is checked before executing the code.
  • In a do-while loop, the code is executed at least once before checking the condition.

Syntax:

do {
    // Code to be executed
} while (condition);

Example 5: Difference Between While and Do-While

#include <stdio.h>

int main() {
    int n = 0;

    printf("Using while loop:\n");
    while (n > 0) {
        printf("This will NOT be printed.\n");
    }

    printf("\nUsing do-while loop:\n");
    do {
        printf("This WILL be printed at least once.\n");
    } while (n > 0);

    return 0;
}

Output:

Using while loop:

Using do-while loop:
This WILL be printed at least once.

Explanation:

  • The while loop does not execute because n > 0 is FALSE.
  • The do-while loop runs once before checking the condition.

3. FOR LOOP

A for loop is an advanced version of the while loop. It allows for a specific range and controlled iterations.

The for loop consists of three components:

  1. Initialization (init) → Sets the starting value. (e.g., i = 1;)
  2. Condition (condition) → Determines when the loop stops. (e.g., i <= 10;)
  3. Increment (increment) → Updates the loop variable. (e.g., i++)

Syntax:

for (initialization; condition; increment) {
    // Code to be executed
}

Example 6: Printing Numbers 1 to 10

#include <stdio.h>

int main() {
    for (int i = 1; i <= 10; i++) {
        printf("%d\n", i);
    }

    return 0;
}

Output:

1
2
3
4
5
6
7
8
9
10

Example 7: Loop with Step Size of 2

#include <stdio.h>

int main() {
    for (int i = 0; i <= 10; i += 2) {
        printf("%d\n", i);
    }

    return 0;
}

Output:

0
2
4
6
8
10

4. SWITCH-CASE STATEMENT

A switch-case statement is an alternative to if-else-if for comparing a variable against multiple fixed values.

  • If the variable matches a case, the corresponding block of code is executed.
  • If no cases match, the default case is executed (if present).
  • The break statement prevents fall-through, meaning once a match is found, execution stops.

Syntax:

switch (variable) {
    case value1:
        // Code to execute
        break;
    case value2:
        // Code to execute
        break;
    default:
        // Code if no cases match
}

Example 8: Simple Menu System

#include <stdio.h>

int main() {
    int choice;

    printf("Select an option:\n");
    printf("1. Start\n");
    printf("2. Settings\n");
    printf("3. Exit\n");
    printf("Enter your choice: ");
    scanf("%d", &choice);

    switch (choice) {
        case 1:
            printf("Game Starting...\n");
            break;
        case 2:
            printf("Opening Settings...\n");
            break;
        case 3:
            printf("Exiting Program...\n");
            break;
        default:
            printf("Invalid Choice!\n");
    }

    return 0;
}

Example Output:

Select an option:
1. Start
2. Settings
3. Exit
Enter your choice: 2
Opening Settings...

Example 9: Days of the Week

#include <stdio.h>

int main() {
    int day;

    printf("Enter a number (1-7) for the day of the week: ");
    scanf("%d", &day);

    switch (day) {
        case 1:
            printf("Sunday\n");
            break;
        case 2:
            printf("Monday\n");
            break;
        case 3:
            printf("Tuesday\n");
            break;
        case 4:
            printf("Wednesday\n");
            break;
        case 5:
            printf("Thursday\n");
            break;
        case 6:
            printf("Friday\n");
            break;
        case 7:
            printf("Saturday\n");
            break;
        default:
            printf("Invalid input! Enter a number between 1 and 7.\n");
    }

    return 0;
}

Example Output:

Enter a number (1-7) for the day of the week: 5
Thursday
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