#include <stdio.h>
#include <math.h>

void pqFormel(double &x1, double &x2, double p, double q)
{
	x1=-p/2 +sqrt((p/2)*(p/2)-q);
	x2=-p/2 -sqrt((p/2)*(p/2)-q);
}
int main(int argc, char* argv[])
{
	double x1,x2,p=0.5,q=0.7;
	//...
	pqFormel(x1,x2,p,q);
	//..
}