Problem with programming assignment

#include <iostream>
#include <cmath>
using namespace std;

double num1, num2, num3; //Inputs - Coefficients a, b, c
double disc; // Output - discriminant

void instruction ();	//function instruction prototype
double getDiscriminant (double, double, double);	//function getDiscriminant prototype
void displayEquation (double, double, double);	//function displayEquation prototype

int main ()//main function:

{	
	instruction (); // call instruction function
	cin >> num1, num2, num3; // get input data
	getDiscriminant (num1, num2, num3); //call function getDiscriminant
	
	if (disc < 0)
	{
		cout << "There are  no real solutions to the equation: " << endl;
		displayEquation (num1, num2, num3); //call function displayEquation	
	}
	else if (disc = 0)
	{
		double root1, root2;
		root1 = (-num2 + sqrt(disc)) / (2 * num1);
		root2 = (-num2 - sqrt(disc)) / (2 * num1);
		
		cout <<  "There are two real solutions, " << root1 << " and " << root2 << ", to the equation: " << endl;
        displayEquation (num1, num2, num3); // 	call function displayEquation	
	}
	else
	{
		double root1;
		root1 = (-num2 + sqrt(disc)) / (2 * num1);
		cout << "There is  one real solution, " << root1 << ", to the equation: " << endl;
        displayEquation (num1, num2, num3);// call function displayEquation 
	}
	return 0; //end of main function
}

	//instruction function:
void instruction ()// Display instructions to user
{
	cout << "Please enter coefficients a, b, and c of a quadratic equation." << endl;
	cout <<  "The computer will calculate whether there are any solutions to the equation." << endl;
}	//end instruction function
	
	
double getDiscriminant (double a, double b, double c)// function definition
{
	disc = pow(b, 2) – 4 * a * c;
	return disc;
}	//end getDiscriminant function

void displayEquation (double a, double b, double c)//function definition
{
	cout << a << "x^2 + " << b << "x + " << c << endl;
}	// end displayEquation function