#define _USE_MATH_DEFINES
#include <stdio.h>
#include <stdlib.h>
#include <math.h>

int main()
{
    char choice=0;
    double a, b, radius, area, perimeter, circumference;

    printf("Enter a 2D shape to compute area and perimeter: a - square, b - rectangle, c - circle\n");

    if(scanf("%c", &choice)!=1)
    printf("Invalid input.");
    else {

switch (choice)
   {
       case 'a':
        printf("Enter the side of the square:\n");
        scanf("%lf", &a);
            if(a <= 0) {
                    printf("Invalid input.");
                    return 0; }

       area=a*a;
       perimeter=4*a;

       printf("Square area is:%f\n", area);
       printf("Square perimeter is:%f\n", perimeter);
       break;

        case 'b':
                printf("Enter the sides of the rectangle:\n");
        scanf("%lf %lf", &a, &b);
                if((a <= 0) || (b <= 0)) {
                    printf("Invalid input.");
                    return 0; }

        area = a*b;
        perimeter = 2*a + 2*b;

        printf("Rectangle area is:%f\n", area);
        printf("Rectangle perimeter is:%f\n", perimeter);
        break;

        case 'c':
                printf("Enter the radius of the circle:\n");
        scanf("%lf", &radius);
                if(radius <= 0) {
                    printf("Invalid input.");
                    return 0; }

            area = M_PI*radius*radius;
            circumference = 2*M_PI*radius;

            printf("Circle area is:%f\n", area);
            printf("Circumference is:%f\n", circumference);
            break;

        default:
                printf("Invalid input.");
                break;
   }
   }
   return 0;

}