Compute area of Circle,Squar,Triangle

#include<stdio.h>
int main()
{
    char ch;

    printf("Enter c to compute area of Circle\n");
    printf("Enter s to compute area of Square\n");
    printf("Enter c to compute area of Triangle\n");

    ch=getchar();
    printf("\n");

    if(ch=='c')
    {
        printf("Enter radius of circle : ");
        scanf("%f",&s1);
        printf("Area is : %f ",3.1416*radius*radius);
    }
    else if(ch=='s')
    {
        printf("Enter Length of first side : ");
        scanf("%f",&s1);
        printf("Enter Length of second side : ");
        scanf("%f",&s2);
        printf("Area is : %f ",s1*s2);
    }
    else if(ch=='t')
    {
        printf("Enter length of base : ");
        scanf("%f",&s1);
        printf("Enter length of hight : ");
        scanf("%f",&s2);
        printf("Area is : %f",(s1*s2)/2.0);
    }

    return 0;
}