Final Answer for volume of a spherical tank not valid - c++

Question

I created this program that is supposed to basically use the formula V=Pi*h^2(3r-h)/3 but my final answer isn't adding up.
For example: if I substitute 1 for the radius and 2 for height, I should get 4.18 but instead through the program I am getting -1.
#include <stdio.h>
#include <stdlib.h>
#include <math.h>
double calculatevolume(double);
double main() {
double radius, height;
double sum; //for storing the radius of the reservoir given by the user
//for storing the calculated volume of the water.
printf("Please enter the Radius in meters first and then the Height in meters right after:\n"); //Displays the message on the screen
scanf("%lf",&radius);
printf("Value of r: %f\n", radius);
scanf("%lf",&height);
printf("Value of h: %f\n", height);
sum = calculatevolume(sum);
printf("For a reservoir of radius: %.2f m\nAnd a water depth: %.2f m\nThe water volume is: %.2f m^3\n",radius,height,sum);
system("PAUSE");
}
double calculatevolume(double sum) {
double radius;
double height;
sum = ((((3 * radius) - height)/3) * 3.14 * height * height);
return sum;
}

Answer 1

Try this code, you should pass height and radius to the function:
#include <stdio.h>
#include <stdlib.h>
#include <math.h>
double calculatevolume(double,double,double);
double main() {
double radius, height;
double sum; //for storing the radius of the reservoir given by the user
//for storing the calculated volume of the water.
printf("Please enter the Radius in meters first and then the Height in meters right after:\n"); //Displays the message on the screen
scanf("%lf", &radius);
printf("Value of r: %f\n", radius);
scanf("%lf", &height);
printf("Value of h: %f\n", , height);
sum = calculatevolume(sum,radius,height);
printf("For a reservoir of radius: %.2f m\nAnd a water depth: %.2f m\nThe water volume is: %.2f m^3\n",radius,height,sum);
system("PAUSE");
}
double calculatevolume(double sum, double radius, double height) {
sum = ((((3 * radius) - height)/3) * 3.14 * height * height);
return sum;
}
You may also delete sum from the function header, it's not necessary to pass it