🟢 Beginner · Lesson 11

if, if-else, else-if Ladder

Q: What is the difference between if and if-else in C?

An if statement runs its block only when the condition is true and does nothing otherwise. An if-else statement runs one block when the condition is true and a second block when it is false, so exactly one of the two always executes.

Q: Can we use if without else in C?

Yes. The else part is optional. You use a plain if when you only need to do something when a condition is true, and no action is required when it is false.

Q: What is an else-if ladder in C?

An else-if ladder chains multiple conditions using if, else if, else if … else. C checks each condition top to bottom and runs the block of the first true condition; the final else handles all remaining cases.

Q: Why does if (a = 5) always run in C?

Because a = 5 is assignment, not comparison. It assigns 5 to a and the expression itself evaluates to 5, which is non-zero (true). To compare, use a == 5 with two equal signs.

The if Statement

The if statement executes a block of code only when a condition is true.

Syntax:

Syntax

if (condition) {
    // Code runs only if condition is true (non-zero)
}

C Language

#include <stdio.h>
int main() {
    int marks = 75;
    if (marks >= 40) {
        printf("Pass!\n");
    }
    printf("Marks: %d\n", marks);
    return 0;
}

Pass! Marks: 75

The if-else Statement

Execute one block if true, another if false.

C Language

#include <stdio.h>
int main() {
    int num;
    printf("Enter a number: ");
    scanf("%d", &num);
    if (num % 2 == 0) {
        printf("%d is Even\n", num);
    } else {
        printf("%d is Odd\n", num);
    }
    return 0;
}

Enter a number: 7 7 is Odd

else-if Ladder

Check multiple conditions one by one. The first true condition executes and the rest are skipped.

C Language – Grade Calculator

#include <stdio.h>
int main() {
    int marks;
    printf("Enter marks (0-100): ");
    scanf("%d", &marks);

    if (marks >= 90) {
        printf("Grade: A+ (Excellent!)\n");
    } else if (marks >= 80) {
        printf("Grade: A (Very Good)\n");
    } else if (marks >= 70) {
        printf("Grade: B (Good)\n");
    } else if (marks >= 60) {
        printf("Grade: C (Average)\n");
    } else if (marks >= 40) {
        printf("Grade: D (Pass)\n");
    } else {
        printf("Grade: F (Fail)\n");
    }
    return 0;
}

Enter marks (0-100): 85 Grade: A (Very Good)

Nested if-else

An if-else inside another if-else. Used for checking multiple interdependent conditions.

C Language – Largest of 3 Numbers

#include <stdio.h>
int main() {
    int a, b, c;
    printf("Enter 3 numbers: ");
    scanf("%d %d %d", &a, &b, &c);

    if (a >= b && a >= c) {
        printf("Largest: %d\n", a);
    } else if (b >= a && b >= c) {
        printf("Largest: %d\n", b);
    } else {
        printf("Largest: %d\n", c);
    }
    return 0;
}

Enter 3 numbers: 45 78 23 Largest: 78

More Example Programs

Leap Year Check

C Language

#include <stdio.h>
int main() {
    int year;
    printf("Enter year: ");
    scanf("%d", &year);
    if ((year % 4 == 0 && year % 100 != 0) || (year % 400 == 0)) {
        printf("%d is a Leap Year\n", year);
    } else {
        printf("%d is NOT a Leap Year\n", year);
    }
    return 0;
}

Enter year: 2024 2024 is a Leap Year

Summary

if — runs block only when condition is true
if-else — runs one block or another based on condition
else-if ladder — checks multiple conditions sequentially
nested if — if inside another if, for complex conditions
Condition in C: any non-zero value = true, 0 = false
Don't use = (assignment) when you mean == (comparison)!

🏋️ Practice

Write programs: (1) Check positive/negative/zero (2) Triangle type from 3 sides (3) Voting eligibility (age >= 18) (4) BMI calculator with category.

Frequently Asked Questions

What is the difference between if and if-else in C?

An if statement runs its block only when the condition is true and does nothing otherwise. An if-else statement runs one block when the condition is true and a second block when it is false, so exactly one of the two always executes.

Can we use if without else in C?

Yes. The else part is optional. You use a plain if when you only need to do something when a condition is true, and no action is required when it is false.

What is an else-if ladder in C?

An else-if ladder chains multiple conditions using if, else if, else if … else. C checks each condition top to bottom and runs the block of the first true condition; the final else handles all remaining cases.

Why does if (a = 5) always run in C?

Because a = 5 is assignment, not comparison. It assigns 5 to a and the expression itself evaluates to 5, which is non-zero (true). To compare, use a == 5 with two equal signs.

What values are treated as true and false in C?

In C, any non-zero value is treated as true and 0 is treated as false. There is no separate boolean type in classic C, so integers act as conditions directly.

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