Polygon Area Calculation method [simple polygon] [C ++]

# Include <iostream>
# Include <cmath>
# Include <windows. h>

Const int num = 4;
// The sides of a polygon cannot be intersecting. Otherwise, the calculation will fail.
// If the area is positive, the front of the multiple sides can be determined. If the area is negative, it indicates the back of the polygon.
Double getarea (point * Ppoint, int nnum)
{
Double S = 0;
For (INT I = 0; I <nNum-1; I ++)
S + = Ppoint [I]. x * Ppoint [I + 1]. Y-Ppoint [I + 1]. x * Ppoint [I]. Y;
S + = Ppoint [nNum-1]. x * Ppoint [0]. Y-Ppoint [0]. x * Ppoint [nNum-1]. Y;
S/= 2.0;
Return S;
}

Int main ()
{
Point Points [num] = {
{0, 0 },
{5, 10 },
{20, 10 },
{15, 5 },
};
Double SS;
Ss = FABS (getarea (points, num ));
STD: cout <SS <STD: Endl;
Return 0;
}

It's okay to use a few simple points for computation. You can use a pen to verify a simple situation.