宏定义：宏求面积

#include
#include
using namespace std;
#define p(a,b,c) (a+b+c)/2
#define S(p,a,b,c) sqrt(p*(p-a)*(p-b)*(p-c))
int main()
{
    double a, b, c;
    cin >> a >> b >> c;
    double p, S;
    p = p(a, b, c);
    S = S(p, a, b, c);
    printf("%.3lf", S);
}