Can anyone tell me what I am missing from this program in order to run it?

#include <iostream>
#include <string>
#include <string.h>

using namespace std;

void getscores(int test1, int test2, int test3);
int calculateave(double);
void calculateminmax(int minimum, int maximum);
void display(int test1, int test2, int test3, int minimum, int maximum, double average);

int main()
{
	int test1, test2, test3, minimum, maximum;
	double average;

	getscores(test1, test2, test3);
	calculateave(average);
	calculateminmax(minimum, maximum);
	display(test1, test2, test3, minimum, maximum, average);

	system("pause");
	return 0;
}
void getscores(int test1, int test2, int test3)
	{
		
		cout << "Enter the first test score  : ";
		cin >> test1;
		cout << "Enter the second test score : ";
		cin >> test2;
		cout << "Enter the third test score : ";
		cin >> test3;
		
			}

int calculateave(int test1, int test2, int test3)
{
	double average;

	average = (test1 + test2 + test3) / 3.0;

	return average;
	}

void calculateminmax(int test1, int test2, int test3, int minimum, int maximum)
{
	
	if (test1 <= test2  && test1 <= test3)
		minimum = test1;
	else if (test2 <= test1 && test2 <= test3)
		minimum = test2;
	else
		minimum = test3;

	if (test1 >= test2  && test1 >= test3)
		maximum = test1;
	else if (test2 >= test1 && test2 >= test3)
		maximum = test2;
	else
		maximum = test3;

}
void display(int test1, int test2, int test3, int minimum, int maximum, double average)
{
	cout << endl << "Results ..." << endl;
	cout << "The test scores are " << test1 << " and " << test2 << " and "
		<< test3 << endl;
	cout << "The average of the test scores is " << average << endl;
	cout << "The minimum test score is " << minimum << endl
		<< "The maximum test score is " << maximum << endl;

	
}