Calling functions! Program to read #s from .txt file, calculate discriminate,

Hey there! If someone could help me with my assignment, I would greatly appreciate it!

This is my problem from my professor:

Write a program (C++) that will read 5 sets of 3 values a, b, c from a file (quad.txt).
Create a function to calculate the discriminate and return either: "positive", "zero" or "negative"
In other words, the function will calculate the discriminate and determine if the discriminate is positive, zero and negative and return the correct string message.
Create a function that will calculate and display a, b, c and the roots or no roots based on the string message returned.
Read another set of a, b, c from a file.
Repeat this for 5 sets of a, b, c.
End

This is what I have so far (basically I have a program that does all of what is stated above, but I need it to call for the functions instead of calculating in main

Code:

//

#include "stdafx.h"
#include<iostream> //required for cout. endl.
#include<fstream>//Required for ifstream, ofstream
#include<cmath> 
using namespace std;

int _tmain(int argc, _TCHAR* argv[])
{
//Declare variables
	double  a, b, c, discriminant;
	float r1, r2;
	
	ifstream fin;
	ofstream  report;


//Open file and read first data line (a, b, c)
	fin.open("quad.txt");
	if(fin.fail() ) //open failed
	{
		cerr<<"File quad.txt could not be opened";
		exit(1); //end execution of the program
    }
	while(!fin.eof())
	{
		fin >> a >> b >> c;
		
		//Calculate discriminant
		discriminant=((b*b)-4*a*c);
		cout << discriminant << endl;
		if(discriminant>0)
		{
			r1=(-1*b+sqrt(discriminant))/(2*a);
			r2=(-1*b-sqrt(discriminant))/(2*a);
			cout<<"r1="<<r1<<"\n";
			cout<<"r2="<<r2<<"\n";
			cout<<"there are two distinct roots";
		}
		else if(discriminant==0)
		{
			r1=(-1*b)/(2*a);
			cout<<"r1="<<r1<<"\n";
			cout<<"there is exactly one distinct real root";
		}
		else
		{
			discriminant=-1*discriminant;
			cout<<"No real roots";
		}
	cout<<"\n";
		system("pause");
	}	


return 0;
}

Thanks guys!

OK, so I have done a bit more progress (see code)...but I'm having trouble with the call for function line:

discriminant=dis_calc(?????); //calling function

do I put a, b, c into the function, or something else?

Thanks in advance for any help!

Code:

//
#include "stdafx.h"
#include<iostream> //required for cout. endl.
#include<fstream>//Required for ifstream, ofstream
#include<cmath> //required for acos().
using namespace std;
double dis_calc(double double double); //Function Prototype

int _tmain(int argc, _TCHAR* argv[])
{
//Declare variables
	double  a, b, c, discriminant;
	double r1, r2;
	
	ifstream fin;
	ofstream  report;

	//prompt user for name of input file
	/*cout<<"enter the name of the input file";
	cin>>filename;*/


//Open file and read first data line (a, b, c)
	fin.open("quad.txt");
	if(fin.fail() ) //open failed
	{
		cerr<<"File quad.txt could not be opened";
		exit(1); //end execution of the program
    }
	while(!fin.eof())
	{
		fin >> a >> b >> c;
		
		//Calculate discriminant

		discriminant=dis_calc(?????); //calling function

		cout << discriminant << endl;
		if(discriminant>0)
		{
			r1=(-1*b+sqrt(discriminant))/(2*a);
			r2=(-1*b-sqrt(discriminant))/(2*a);
			cout<<"r1="<<r1<<"\n";
			cout<<"r2="<<r2<<"\n";
			cout<<"there are two distinct roots";
		}
		else if(discriminant==0)
		{
			r1=(-1*b)/(2*a);
			cout<<"r1="<<r1<<"\n";
			cout<<"there is exactly one distinct real root";
		}
		else
		{
			discriminant=-1*discriminant;
			cout<<"No real roots";
		}
	cout<<"\n";
		system("pause");
	}	


return 0;
}

	
double dis_calc(double a, double b, double c)
{
	double discriminant=((b*b)-4*a*c);
	return discriminant;
}