#include <stdio.h>
#include <math.h>
#define PI 3.14159   // Constant value of PI
 
int main() {
    int choice, n;
    float length, width, radius, side, base1, base2, height;
    float a, b, c, d;  // Sides
    float area, perimeter, circumference, s, major_axis, minor_axis;
 
    // Display Menu
    printf("=== Geometry Calculator ===\n");
    printf("1. Rectangle (Area & Perimeter)\n");
    printf("2. Circle (Area & Circumference)\n");
    printf("3. Square (Area & Perimeter)\n");
    printf("4. Triangle (Area & Perimeter)\n");
    printf("5. Trapezium (Area)\n");
    printf("6. Parallelogram (Area & Perimeter)\n");
    printf("7. Rhombus (Area & Perimeter)\n");
    printf("8. Ellipse (Area & Approx. Perimeter)\n");
    printf("9. Regular Polygon (Area & Perimeter)\n");
    printf("Enter your choice (1-9): ");
    scanf("%d", &choice);
 
    switch(choice) {
        case 1: // Rectangle
            printf("\nEnter length: ");
            scanf("%f", &length);
            printf("Enter width: ");
            scanf("%f", &width);
            area = length * width;
            perimeter = 2 * (length + width);
            printf("Area of Rectangle      = %.2f\n", area);
            printf("Perimeter of Rectangle = %.2f\n", perimeter);
            break;
 
        case 2: // Circle
            printf("\nEnter radius: ");
            scanf("%f", &radius);
            area = PI * radius * radius;
            circumference = 2 * PI * radius;
            printf("Area of Circle          = %.2f\n", area);
            printf("Circumference of Circle = %.2f\n", circumference);
            break;
 
        case 3: // Square
            printf("\nEnter side: ");
            scanf("%f", &side);
            area = side * side;
            perimeter = 4 * side;
            printf("Area of Square      = %.2f\n", area);
            printf("Perimeter of Square = %.2f\n", perimeter);
            break;
 
        case 4: // Triangle (Heron’s formula)
            printf("\nEnter sides (a, b, c): ");
            scanf("%f %f %f", &a, &b, &c);
            perimeter = a + b + c;
            s = perimeter / 2;
            area = sqrt(s * (s - a) * (s - b) * (s - c));
            printf("Perimeter of Triangle = %.2f\n", perimeter);
            printf("Area of Triangle      = %.2f\n", area);
            break;
 
        case 5: // Trapezium
            printf("\nEnter base1: ");
            scanf("%f", &base1);
            printf("Enter base2: ");
            scanf("%f", &base2);
            printf("Enter height: ");
            scanf("%f", &height);
            area = 0.5 * (base1 + base2) * height;
            printf("Area of Trapezium = %.2f\n", area);
            break;
 
        case 6: // Parallelogram
            printf("\nEnter base: ");
            scanf("%f", &base1);
            printf("Enter height: ");
            scanf("%f", &height);
            printf("Enter side length: ");
            scanf("%f", &side);
            area = base1 * height;
            perimeter = 2 * (base1 + side);
            printf("Area of Parallelogram      = %.2f\n", area);
            printf("Perimeter of Parallelogram = %.2f\n", perimeter);
            break;
 
        case 7: // Rhombus
            printf("\nEnter diagonals d1 and d2: ");
            scanf("%f %f", &a, &b);
            printf("Enter side length: ");
            scanf("%f", &side);
            area = (a * b) / 2;
            perimeter = 4 * side;
            printf("Area of Rhombus      = %.2f\n", area);
            printf("Perimeter of Rhombus = %.2f\n", perimeter);
            break;
 
        case 8: // Ellipse
            printf("\nEnter major axis (a): ");
            scanf("%f", &major_axis);
            printf("Enter minor axis (b): ");
            scanf("%f", &minor_axis);
            area = PI * major_axis * minor_axis;
            // Approximation (Ramanujan’s formula)
            perimeter = PI * (3*(major_axis+minor_axis) - sqrt((3*major_axis+minor_axis)*(major_axis+3*minor_axis)));
            printf("Area of Ellipse      = %.2f\n", area);
            printf("Perimeter of Ellipse ≈ %.2f\n", perimeter);
            break;
 
        case 9: // Regular Polygon
            printf("\nEnter number of sides (n): ");
            scanf("%d", &n);
            printf("Enter side length: ");
            scanf("%f", &side);
            perimeter = n * side;
            area = (n * side * side) / (4 * tan(PI / n));
            printf("Area of Polygon      = %.2f\n", area);
            printf("Perimeter of Polygon = %.2f\n", perimeter);
            break;
 
        default:
            printf("\nInvalid choice! Please select 1–9.\n");
    }
 
    return 0;
}