Control Structures in C

2.1 if Statement

Executes a block only if the condition is true.

Syntax

if (condition) {
    // executes if condition is true
}

Example

#include <stdio.h>

int main() {
    int x = 10;

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

    printf("Program continues...\n");
    return 0;
}

2.2 if-else Statement

Provides two paths:

• if condition is true → run if block
• else → run else block

Syntax

if (condition) {
    // true block
} else {
    // false block
}

Example (Even/Odd)

#include <stdio.h>

int main() {
    int num = 4956;

    if (num % 2 == 0) {
        printf("%d is Even\n", num);
    } else {
        printf("%d is Odd\n", num);
    }

    return 0;
}

2.3 Nested if / Nested if-else

An if (or if-else) inside another if block for more complex decisions.

Syntax

if (condition1) {
    if (condition2) {
        // both true
    } else {
        // condition1 true, condition2 false
    }
} else {
    // condition1 false
}

Example

#include <stdio.h>

int main() {
    int x = 15;

    if (x > 10) {
        if (x < 20) {
            printf("x is between 10 and 20\n");
        } else {
            printf("x is 20 or more\n");
        }
    } else {
        printf("x is 10 or less\n");
    }

    return 0;
}

2.4 if - else if - else Ladder

Used when you have multiple conditions to test in order.
The first true condition runs, and the rest are skipped.

Syntax

if (condition1) {
    // ...
} else if (condition2) {
    // ...
} else if (condition3) {
    // ...
} else {
    // none matched
}

Example (Positive/Negative/Zero)

#include <stdio.h>

int main() {
    int number = 0;

    if (number > 0) {
        printf("The number is Positive\n");
    } else if (number < 0) {
        printf("The number is Negative\n");
    } else {
        printf("The number is Zero\n");
    }

    return 0;
}

✅ Tip: Ladder is different from nested if because it checks conditions sequentially at the same level.

2.5 switch Statement

Best when you compare one expression against many constant values.

Syntax

switch (expression) {
    case value1:
        // ...
        break;
    case value2:
        // ...
        break;
    default:
        // ...
}

Example

#include <stdio.h>

int main() {
    int day = 3;

    switch (day) {
        case 1: printf("Sunday"); break;
        case 2: printf("Monday"); break;
        case 3: printf("Tuesday"); break;
        default: printf("Invalid day");
    }

    return 0;
}

Important: If you forget break, C will fall through into the next case.

2.6 Ternary Operator ?:

Short form of if-else when assigning/returning a value.

Syntax

condition ? expr_if_true : expr_if_false;

Example

#include <stdio.h>

int main() {
    int x = 5;
    int result = (x > 0) ? 1 : 0;
    printf("Result: %d\n", result);
    return 0;
}