Example: Shape Measurement Calculator in C

// Shape Measurement Calculator
#include <stdio.h>
#include <math.h>

// Define M_PI if not available in math.h (e.g., on some compilers)
#ifndef M_PI
#define M_PI 3.14159265358979323846
#endif

// Function to calculate rectangle properties
void calculateRectangle() {
    float length, width, area, perimeter;
    printf("\n--- Rectangle Calculator ---\n");
    printf("Enter the length of the rectangle: ");
    scanf("%f", &length);
    printf("Enter the width of the rectangle: ");
    scanf("%f", &width);
    if (length <= 0 || width <= 0) {
        printf("Error: Length and width must be positive values.\n");
        return;
    }
    area = length * width;
    perimeter = 2 * (length + width);
    printf("Area of the rectangle: %.2f\n", area);
    printf("Perimeter of the rectangle: %.2f\n", perimeter);
}

// Function to calculate circle properties
void calculateCircle() {
    float radius, area, circumference;
    printf("\n--- Circle Calculator ---\n");
    printf("Enter the radius of the circle: ");
    scanf("%f", &radius);
    if (radius <= 0) {
        printf("Error: Radius must be a positive value.\n");
        return;
    }
    area = M_PI * radius * radius;
    circumference = 2 * M_PI * radius;
    printf("Area of the circle: %.2f\n", area);
    printf("Circumference of the circle: %.2f\n", circumference);
}

// Function to calculate triangle properties
void calculateTriangle() {
    float side1, side2, side3, perimeter, semiPerimeter, area;
    printf("\n--- Triangle Calculator ---\n");
    printf("Enter the length of side 1: ");
    scanf("%f", &side1);
    printf("Enter the length of side 2: ");
    scanf("%f", &side2);
    printf("Enter the length of side 3: ");
    scanf("%f", &side3);
    if (side1 <= 0 || side2 <= 0 || side3 <= 0) {
        printf("Error: Side lengths must be positive values.\n");
        return;
    }
    // Triangle inequality theorem check
    if (!((side1 + side2 > side3) && (side1 + side3 > side2) && (side2 + side3 > side1))) {
        printf("Error: The given side lengths do not form a valid triangle.\n");
        return;
    }
    perimeter = side1 + side2 + side3;
    semiPerimeter = perimeter / 2;
    area = sqrt(semiPerimeter * (semiPerimeter - side1) * (semiPerimeter - side2) * (semiPerimeter - side3));
    printf("Perimeter of the triangle: %.2f\n", perimeter);
    printf("Area of the triangle: %.2f\n", area);
}

int main() {
    int choice;
    do {
        printf("\n--- Shape Measurement Menu ---\n");
        printf("1. Calculate Rectangle\n");
        printf("2. Calculate Circle\n");
        printf("3. Calculate Triangle\n");
        printf("4. Exit\n");
        printf("Enter your choice: ");
        scanf("%d", &choice);

        switch (choice) {
            case 1:
                calculateRectangle();
                break;
            case 2:
                calculateCircle();
                break;
            case 3:
                calculateTriangle();
                break;
            case 4:
                printf("Exiting program. Goodbye!\n");
                break;
            default:
                printf("Invalid choice. Please enter a number between 1 and 4.\n");
        }
    } while (choice != 4);

    return 0;
}