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Decision Making Programs in C

Menu-driven program: area of circle, rectangle, triangle

Introduction

A menu-driven program allows the user to choose from a list of operations.
In this example, the program calculates:

  1. Area of a Circle → π × r²
  2. Area of a Rectangle → length × breadth
  3. Area of a Triangle → 5 × base × height

We’ll use switch-case for cleaner menu handling.

C Program: Menu-driven program: area of circle, rectangle, triangle

C 
#include <stdio.h>


#define PI 3.14159


 


int main() {


    int choice;


    float radius, length, breadth, base, height, area;


 


    // Display Menu


    printf("=== AREA CALCULATOR ===\n");


    printf("1. Area of Circle\n");


    printf("2. Area of Rectangle\n");


    printf("3. Area of Triangle\n");


    printf("Enter your choice (1-3): ");


    scanf("%d", &choice);


 


    switch (choice) {


        case 1:


            // Circle Area


            printf("Enter radius of the circle: ");


            scanf("%f", &radius);


            area = PI * radius * radius;


            printf("Area of Circle = %.2f\n", area);


            break;


 


        case 2:


            // Rectangle Area


            printf("Enter length and breadth of rectangle: ");


            scanf("%f %f", &length, &breadth);


            area = length * breadth;


            printf("Area of Rectangle = %.2f\n", area);


            break;


 


        case 3:


            // Triangle Area


            printf("Enter base and height of triangle: ");


            scanf("%f %f", &base, &height);


            area = 0.5 * base * height;


            printf("Area of Triangle = %.2f\n", area);


            break;


 


        default:


            printf("Invalid choice! Please enter 1, 2, or 3.\n");


    }


 


    return 0;


}

Output

 
OUTPUT 1 :
=== AREA CALCULATOR ===
1. Area of Circle
2. Area of Rectangle
3. Area of Triangle
Enter your choice (1-3): 1
Enter radius of the circle: 5
Area of Circle = 78.54

OUTPUT 2 :
=== AREA CALCULATOR ===
1. Area of Circle
2. Area of Rectangle
3. Area of Triangle
Enter your choice (1-3): 2
Enter length and breadth of rectangle: 10 5
Area of Rectangle = 50.00

OUTPUT 3 :
=== AREA CALCULATOR ===
1. Area of Circle
2. Area of Rectangle
3. Area of Triangle
Enter your choice (1-3): 3
Enter base and height of triangle: 8 6
Area of Triangle = 24.00

Explanation

  1. A menu is displayed with 3 options.
  2. The user enters a choice.
  3. Using switch(choice), the program:
    • Calculates circle area if choice == 1.
    • Calculates rectangle area if choice == 2.
    • Calculates triangle area if choice == 3.
  4. If the choice is invalid, an error message is shown.
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