Parabola Coordinates Program

#include <stdio.h>
#include <iostream.h>
#include <math.h>
int main()
{
 double a, b, c, x1, x2, vp, z;
 printf("Please enter a, b, and c of your quadratic equation (in that order): ");
 cin >> a;
 cin >> b;
 cin >> c;
 
 
 x1 = (-b + sqrt(b*b - 4*a*c))/(2*a); //First x-intercept
 x2 = (-b - sqrt(b*b - 4*a*c))/(2*a); //Second x-intercept
 z = -b/(2*a);
 vp = (a*z)*(a*z) + (b*z) + c;     //Vertex point
 printf("The x-intercepts are %lg and %lg\n", x1, x2);
 printf("The y-intercept is %lg\n", c);
 printf("The vertex point is %lg , %lg\n", z, vp);
 return 0;
}