求三角形面积

#include <stdio.h>
#include <math.h>
double zxd (double a, double b, double c);
int main()
{
    double  a, b, c;
    scanf("%lf %lf %lf",&a, &b, &c);
    double s = zxd (a, b, c);
    printf("%.3lf",s);
    return 0;
}
double zxd  (double a, double b, double c)
{
    double p;
    double s;
    p = (a+b+c)/2.0;
    s = sqrt(p*(p-a)*(p-b)*(p-c));
    return s;
}