hi everyone! i'm trying to do some homework and this program i wrote that's supposed to read in numbers and do some calculations isn't working right. The problem right now is that no matter what number i put in for radius it gives me the invalid number result, please help me and thanks in advance.

Code:#include <stdio.h> #define PI 3.141593 int main (void) { double len, rad, SA, vol; printf("Enter the length of the tank\(feet\)\n"); scanf("%lf", &len); while(len<10 || len>20) { printf("Invalid length, please try again.\n"); scanf("%lf", &len); } printf("Enter the radius of the tank\(feet\)\n"); scanf("%lf", &rad); while(rad<3 || rad>6) { printf("Invalid radius, please try again.\n"); scanf("%lf", &rad); } while(2*rad>=len) { printf("Non-real tank,Invalid input, please try again.\n"); printf("Enter the length of the tank\(feet\)\n"); scanf("%lf", &len); while(len<10 || len>20) { printf("Invalid input, please try again.\n"); scanf("%lf", &len); } printf("Enter the radius of the tank\(feet\)\n"); scanf("%lf", &rad); while(rad<3 || len>6) { printf("Invalid input, please try again.\n"); scanf("%lf", &rad); } } vol = (PI*rad*rad*len)-(4/3*PI*rad*rad*rad); SA = (2*PI*rad*len)+(4*PI*rad*rad); printf("A cylindrical tank of length %.3lf and radius %.3lf with inverted spherical \ncaps has\nvolume: %.3lf\nand\nsurface area: %lf",len, rad, vol, SA); return 0; }