/****************************************************
* This program calculates the internal surface of a *
* polygon defined by n points of coordinates:       *
*         x1, y1, x2, y2,...xn, yn.                 *
* ------------------------------------------------- *
* Ref.: "Mathématiques en Turbo-Pascal By M. Ducamp *
* and A. Reverchon (vol 2), Eyrolles, Paris, 1988"  *
* [BIBLI 05].                                       * 
* ------------------------------------------------- *
* SAMPLE RUN:                                       *
*                                                   *
* npoints=13                                        *
* x1=3    y1=3                                      *
* x2=12   y2=3                                      *
* x3=12   y3=6                                      *
* x4=11   y4=6                                      *
* x5=11   y5=7                                      *
* x6=15   y6=7                                      *
* x7=15   y7=9                                      *
* x8=8    y8=9                                      *
* x9=8    y9=6                                      *
* x10=4   y10=6                                     *
* x11=4   y11=9                                     *
* x12=3   y12=9                                     *
* x13=3   y13=3                                     *
*                                                   *
* Surface is: 47.000000                             *
*                                                   *
*                        C++ version by J-P Moreau. *
*                            (www.jpmoreau.fr)      *
****************************************************/
#include <stdio.h>
#include <math.h>

#define  NMAX  50

float s;
int   i, npoints;
float buffer[NMAX][NMAX];

void main() {
  s=0;
  npoints=13;                    //13 points
  //init buffer x(i), y(i) }
  for (i=1; i<=npoints; i++)  {
    buffer[1][1]= 3; buffer[1][2]=3;
    buffer[2][1]=12; buffer[2][2]=3;
    buffer[3][1]=12; buffer[3][2]=6;
    buffer[4][1]=11; buffer[4][2]=6;
    buffer[5][1]=11; buffer[5][2]=7;
    buffer[6][1]=15; buffer[6][2]=7;
    buffer[7][1]=15; buffer[7][2]=9;
    buffer[8][1]= 8; buffer[8][2]=9;
    buffer[9][1]= 8; buffer[9][2]=6;
    buffer[10][1]=4; buffer[10][2]=6;
    buffer[11][1]=4; buffer[11][2]=9;
    buffer[12][1]=3; buffer[12][2]=9;
    buffer[13][1]=3; buffer[13][2]=3;
  }
  //calculate internal surface
  for (i=1; i<npoints; i++) {
    s+=(buffer[i][1]+buffer[i+1][1])*(buffer[i][2]-buffer[i+1][2]);
  }
  s=(float) (fabs(s)/2);
  //print surface
  printf("\n Surface is: %f\n\n\n",s);
}

// end of file surface.cpp