Найти площадь пятиугольника

#include<mach.h> 
#include "stdafx.h"
 
int main() { 
Double a,b,c,d,e,f,g,S,s1,s2,s3,p1,p2,p3;
p1=(a+b+g)/2;
s1=sqrt(p1*(p1-a)(p1-b)(p1-g));
return 0;
}

#include<mach.h> 
#include "stdafx.h"
 
int main() { 
double a,b,c,d,e,f,g,S,s1,s2,s3,p1,p2,p3;
p1=(a+b+g)/2;
p2=(f+g+c)/2;
p3=(e+f+d)/2;
s1=sqrt(p1*(p1-a)(p1-b)(p1-g));
s2=sqrt(p2*(p2-f)(p2-g)(p2-c));
s3=sqrt(p3*(p3-e)(p3-f)(p3-d));
S=s1+s2+s3;
return 0;
}

#include "stdafx.h"
#include"math.h"
 
 
 
 
int _tmain(int argc, _TCHAR* argv[])
{
    double a, b, c, d, e, f, g, S, s1, s2, s3, p1, p2, p3;
    /*a = 4;
    b = 6;
    c = 7;
    d = 7;
    e = 1;
    f = 5;
    g = 9;*/
 
    p1 = (a + b + g) / 2;
    p2 = (f + g + c) / 2;
    p3 = (e + f + d) / 2;
    s1 = sqrt(p1*(p1 - a)*(p1 - b)*(p1 - g));
    s2 = sqrt(p2*(p2 - f)*(p2 - g)*(p2 - c));
    s3 = sqrt(p3*(p3 - e)*(p3 - f)*(p3 - d));
    S = s1 + s2 + s3;
    return 0;
}