Quadratic equation solver

#include <iostream>
#include <cmath>
#include <string>
#include <conio.h>
#include <stdlib.h>
#include <locale>

//Quadratic equation solver

using namespace std;

int D, a, b, c, x1, x2;
double qq;

int main(){
    cout << "Sqrt is a sqare root\n";
    cout << "Enter a\n";
    cin >> a;
    cout << "Enter b\n";
    cin >> b;
    cout << "Enter c\n";
    cin >> c;
    D = (pow(b, 2) - (4 * a * c));
    if (D < 0){
        cout << "X1, X2 = varnothing\n";
        system("pause");
        return 0;
    }
    else if (D == 0){
        x1 = (b * -1) / (2 * a);
        x2 = x1;
    }
    else{
        qq = sqrt(D);
        if (D / qq == qq){
            x1 = ((b * -1) - qq) / (2 * a);
            x2 = ((b * -1) + qq) / (2 * a);
        }
        else{
            a = a * 2;
            cout << "X1 = -" << b << " - sqrt of" << D << "/ " << a << "\n";
            cout << "X2 = -" << b << " + sqrt of" << D << "/ " << a << "\n";
            system("pause");
            return 0;
        }
    }

    cout << "X1 = " << x1 << "\nX2 = " << x2 << "\n";
    system("pause");
    return 0;
}