CDecision StatementsNested If Statement

Understanding Nested if Statements in C: A Beginner’s Guide

The nested if statement in C allows you to check multiple conditions in a hierarchical manner. It is essentially an if statement inside another if or else block. This enables your program to make decisions that depend on multiple criteria.

In this blog, we’ll explore nested if statements in depth, including syntax, examples, and practical applications with detailed explanations.

1. What is a Nested if Statement?

A nested if statement is an if statement that appears inside another if or else block. This structure is useful when a decision depends on multiple levels of conditions.

Syntax:

if (condition1) {
    if (condition2) {
        // Code to execute if both condition1 and condition2 are true
    } else {
        // Code to execute if condition1 is true but condition2 is false
    }
} else {
    // Code to execute if condition1 is false
}
  • The outer if evaluates condition1.
  • If condition1 is true, the inner if evaluates condition2.
  • If condition1 is false, the program executes the else block.

2. Basic Example

Let’s start with a simple nested if example to check if a number is positive, negative, or zero.

main.c
#include <stdio.h>
 
int main() {
    int number;
 
    printf("Enter a number: ");
    scanf("%d", &number);
 
    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 if (number < 0) {
        printf("The number is negative.\n");
    } else {
        printf("The number is zero.\n");
    }
 
    return 0;
}

Output (Examples):

  1. Input: 4 
    The number is positive and even.
  2. Input: -3 
    The number is negative.
  3. Input: 0 
    The number is zero.

3. Practical Applications of Nested if

1. Determining a Student’s Grade

This program assigns grades based on marks:

- **Marks >= 90**: Grade A
- **Marks >= 75 but < 90**: Grade B
- **Marks >= 50 but < 75**: Grade C
- **Marks < 50**: Fail
main.c
#include <stdio.h>
 
int main() {
    int marks;
 
    printf("Enter your marks: ");
    scanf("%d", &marks);
 
    if (marks >= 50) {
        if (marks >= 90) {
            printf("You scored Grade A.\n");
        } else if (marks >= 75) {
            printf("You scored Grade B.\n");
        } else {
            printf("You scored Grade C.\n");
        }
    } else {
        printf("You failed the exam.\n");
    }
 
    return 0;
}

Output (Examples):

  1. Input: 95 
    You scored Grade A.
  2. Input: 80 
    You scored Grade B.
  3. Input: 45 
    You failed the exam.

2. Finding the Largest of Three Numbers

This program uses nested if statements to identify the largest number among three.

main.c
#include <stdio.h>
 
int main() {
    int a, b, c;
 
    printf("Enter three numbers: ");
    scanf("%d %d %d", &a, &b, &c);
 
    if (a >= b) {
        if (a >= c) {
            printf("%d is the largest number.\n", a);
        } else {
            printf("%d is the largest number.\n", c);
        }
    } else {
        if (b >= c) {
            printf("%d is the largest number.\n", b);
        } else {
            printf("%d is the largest number.\n", c);
        }
    }
 
    return 0;
}

Output (Examples):

  1. Input: 5 10 8 
    10 is the largest number.
  2. Input: 12 4 12 
    12 is the largest number.

4. Advanced Example: Calculating Income Tax

This program calculates income tax based on income brackets:

- **Income <= 250,000**: No tax
- **Income > 250,000 but <= 500,000**: 5% tax
- **Income > 500,000 but <= 1,000,000**: 20% tax
- **Income > 1,000,000**: 30% tax
main.c
#include <stdio.h>
 
int main() {
    double income, tax;
 
    printf("Enter your annual income: ");
    scanf("%lf", &income);
 
    if (income > 250000) {
        if (income <= 500000) {
            tax = (income - 250000) * 0.05;
        } else if (income <= 1000000) {
            tax = (250000 * 0.05) + ((income - 500000) * 0.20);
        } else {
            tax = (250000 * 0.05) + (500000 * 0.20) + ((income - 1000000) * 0.30);
        }
        printf("Your tax amount is: %.2lf\n", tax);
    } else {
        printf("No tax applicable.\n");
    }
 
    return 0;
}

Output (Examples):

  1. Input: 400000 
    Your tax amount is: 7500.00
  2. Input: 1200000 
    Your tax amount is: 190000.00

5. Key Points to Remember

  • Braces {} are essential: Always use braces for clarity, even if a block contains only one statement.
  • Nested if statements can become complex. Use proper indentation to improve readability.
  • Avoid deep nesting: For highly complex logic, consider using other constructs like switch or functions.

Summary

The nested if statement provides a way to check multiple conditions in a hierarchical structure. It is particularly useful for problems that require multiple levels of decision-making, like grading systems, tax calculations, or comparing numbers.

By mastering nested if statements, you’ll gain a powerful tool for solving complex programming problems efficiently. In the next post, we’ll dive into switch statements, another tool for decision-making in C. Stay tuned!

If-Else StatementSwitch Statement