CDecision StatementsSwitch Statement

Understanding the switch Statement in C: A Beginner’s Guide

The switch statement in C is a powerful control structure that simplifies complex decision-making. It provides an alternative to using multiple if-else conditions, especially when checking a variable against several fixed values.

In this blog, we’ll explore the syntax, use cases, and practical examples of switch statements, along with detailed explanations.

1. What is a switch Statement?

The switch statement allows a variable to be tested for equality against multiple values. Each value is called a case, and the variable is compared to each case.

Syntax:

switch (expression) {
    case value1:
        // Code to execute if expression equals value1
        break;
    case value2:
        // Code to execute if expression equals value2
        break;
    ...
    default:
        // Code to execute if no case matches
}

Key Points:

  1. The expression must evaluate to an integer or character.
  2. The case keyword is followed by a constant value.
  3. break exits the switch block. Without it, execution continues to the next case (fall-through behavior).
  4. The default case is optional and runs if no case matches.

2. Basic Example

Let’s start with a simple example: selecting a day of the week based on user input.

main.c
#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("Monday\n");
            break;
        case 2:
            printf("Tuesday\n");
            break;
        case 3:
            printf("Wednesday\n");
            break;
        case 4:
            printf("Thursday\n");
            break;
        case 5:
            printf("Friday\n");
            break;
        case 6:
            printf("Saturday\n");
            break;
        case 7:
            printf("Sunday\n");
            break;
        default:
            printf("Invalid input! Please enter a number between 1 and 7.\n");
    }
 
    return 0;
}

Output (Examples):

  1. Input: 3 
    Wednesday
  2. Input: 8 
    Invalid input! Please enter a number between 1 and 7.

3. Practical Applications of switch

1. Calculator Program

This program performs basic arithmetic operations (+, -, *, /) based on the user’s choice.

main.c
#include <stdio.h>
 
int main() {
    char operator;
    double num1, num2, result;
 
    printf("Enter an operator (+, -, *, /): ");
    scanf(" %c", &operator);
 
    printf("Enter two numbers: ");
    scanf("%lf %lf", &num1, &num2);
 
    switch (operator) {
        case '+':
            result = num1 + num2;
            printf("Result: %.2lf\n", result);
            break;
        case '-':
            result = num1 - num2;
            printf("Result: %.2lf\n", result);
            break;
        case '*':
            result = num1 * num2;
            printf("Result: %.2lf\n", result);
            break;
        case '/':
            if (num2 != 0) {
                result = num1 / num2;
                printf("Result: %.2lf\n", result);
            } else {
                printf("Error: Division by zero is not allowed.\n");
            }
            break;
        default:
            printf("Invalid operator!\n");
    }
 
    return 0;
}

Output (Examples):

  1. Input: + and 5 3 
    Result: 8.00
  2. Input: / and 4 0 
    Error: Division by zero is not allowed.

2. Grading System

This program assigns grades based on marks using a switch statement.

main.c
#include <stdio.h>
 
int main() {
    int marks;
 
    printf("Enter your marks (0-100): ");
    scanf("%d", &marks);
 
    switch (marks / 10) {
        case 10:
        case 9:
            printf("Grade A\n");
            break;
        case 8:
        case 7:
            printf("Grade B\n");
            break;
        case 6:
        case 5:
            printf("Grade C\n");
            break;
        default:
            if (marks >= 0 && marks < 50) {
                printf("Fail\n");
            } else {
                printf("Invalid marks entered.\n");
            }
    }
 
    return 0;
}

Output (Examples):

  1. Input: 85 
    Grade B
  2. Input: 45 
    Fail

3. Finding the Type of Triangle

This program determines the type of triangle based on user input for the sides.

main.c
#include <stdio.h>
 
int main() {
    int a, b, c;
 
    printf("Enter the three sides of the triangle: ");
    scanf("%d %d %d", &a, &b, &c);
 
    if (a + b > c && a + c > b && b + c > a) { // Check if it's a valid triangle
        switch ((a == b) + (b == c) + (a == c)) {
            case 3:
                printf("The triangle is Equilateral.\n");
                break;
            case 1:
                printf("The triangle is Isosceles.\n");
                break;
            default:
                printf("The triangle is Scalene.\n");
        }
    } else {
        printf("The sides do not form a valid triangle.\n");
    }
 
    return 0;
}

Output (Examples):

  1. Input: 5 5 5 
    The triangle is Equilateral.
  2. Input: 3 4 5 
    The triangle is Scalene.

4. Advanced Example: Converting Numbers to Words

This program converts single-digit numbers into words.

main.c
#include <stdio.h>
 
int main() {
    int number;
 
    printf("Enter a single-digit number (0-9): ");
    scanf("%d", &number);
 
    switch (number) {
        case 0:
            printf("Zero\n");
            break;
        case 1:
            printf("One\n");
            break;
        case 2:
            printf("Two\n");
            break;
        case 3:
            printf("Three\n");
            break;
        case 4:
            printf("Four\n");
            break;
        case 5:
            printf("Five\n");
            break;
        case 6:
            printf("Six\n");
            break;
        case 7:
            printf("Seven\n");
            break;
        case 8:
            printf("Eight\n");
            break;
        case 9:
            printf("Nine\n");
            break;
        default:
            printf("Invalid input! Enter a single-digit number.\n");
    }
 
    return 0;
}

Output (Examples):

  1. Input: 5 
    Five
  2. Input: 12 
    Invalid input! Enter a single-digit number.

5. Key Points to Remember

  1. Use break statements to prevent fall-through.
  2. The default case is optional but improves the program’s robustness.
  3. switch works well when checking a variable against discrete, fixed values (e.g., days, grades, numbers).
  4. Avoid using complex expressions or ranges directly in case. Use division, modular arithmetic, or preprocessing logic instead.

Summary

The switch statement in C is a clean and efficient way to handle multi-condition scenarios where a variable is compared to fixed values. It is especially useful in programs like calculators, menu-driven applications, and simple decision-making tasks.

In the next blog, we’ll explore loops in C, which allow repetitive execution of code. Stay tuned!

Nested If StatementFor Loop