C program to call the user-defined function through switch() statement

#include<stdio.h>
#include<conio.h>
#include<math.h>
#include<ctype.h>

void main()
{
    int a();
    int x=5;

    clrscr();

    switch(a())
    {
        case's':
            printf("Square of %d is %f", x, pow(x,2));
            break;

        case'c':
            printf("Cube of %d is %f",x,pow(x,3));
            break;
        case'd':
            printf("Double of %d is %d",x,x*2);
            break;
        default:
            printf("Unexpected choice printed as it is: %d", x);
    }
}
int a()
{
    char c='c';

    printf("Enter your choice square(s), cube(c), double(d): ");

    c=getchar();
    c=tolower(c);

    return(c);
}

Enter your choice square(s), cube(c), double(d): D
Double of 5 is 10