C If Else

The if...else statement in C is a conditional control structure that allows you to execute different blocks of code depending on whether a specified condition is true or false. It is one of the most commonly used decision-making structures in C programming.

Syntax

if (condition) {
    // Code to execute if the condition is true
} else {
    // Code to execute if the condition is false
}

• condition: A Boolean expression (or any expression that can be evaluated to true or false).
• true: The block of code inside the if part is executed if the condition is true (non-zero).
• false: The block of code inside the else part is executed if the condition is false (zero).

Example 1: Basic if...else

#include <stdio.h>

int main() {
    int number = 10;

    if (number > 0) {
        printf("The number is positive.\n");
    } else {
        printf("The number is non-positive.\n");
    }

    return 0;
}

Output:

The number is positive.

Example 2: if...else with Different Conditions

You can use multiple conditions with the if...else statement to handle different cases.

#include <stdio.h>

int main() {
    int number = -5;

    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;
}

Output:

The number is negative.

Example 3: Nested if...else

You can also nest if...else statements inside each other to handle more complex conditions.

#include <stdio.h>

int main() {
    int number = 7;

    if (number > 0) {
        if (number % 2 == 0) {
            printf("The number is positive and even.\n");
        } else {
            printf("The number is positive and odd.\n");
        }
    } else {
        printf("The number is non-positive.\n");
    }

    return 0;
}

Output:

The number is positive and odd.

Example 4: if...else with Boolean Expressions

The condition in the if statement can be any expression that evaluates to a Boolean value (either true or false).

#include <stdio.h>

int main() {
    int x = 3, y = 5;

    if (x == y) {
        printf("x and y are equal.\n");
    } else {
        printf("x and y are not equal.\n");
    }

    return 0;
}

Output:

x and y are not equal.

Example 5: if...else with Logical Operators

You can combine multiple conditions using logical operators (&& for AND, || for OR) in the if condition.

#include <stdio.h>

int main() {
    int age = 25;
    int hasLicense = 1;  // 1 represents true, 0 represents false

    if (age >= 18 && hasLicense) {
        printf("You are eligible to drive.\n");
    } else {
        printf("You are not eligible to drive.\n");
    }

    return 0;
}

Output:

You are eligible to drive.

Summary

• The if...else statement evaluates a condition, and based on whether it’s true or false, it executes one of two blocks of code.
• You can chain multiple else if clauses to handle more than two possible conditions.
• Conditions can include relational comparisons, logical operators, and complex expressions.
• It’s a foundational control structure for making decisions in C programs.