// Example 4-5：求三角形面積
#include <iostream.h>
#include <math.h>
void main()
{
	double a, b, c, s, area;
	cout << "please input a, b, c =?";
	cin >> a >> b >> c;
	s = (a+b+c)/2;
	area = sqrt(s*(s-a)*(s-b)*(s-c));
	cout << "area = " << area;
}