ernie.WPI.EDU> cat exam04_01.C

// file exam04_01.C, cs2223, D97/98 //

// 28Apr98 NW, First version

// includes
#include "headers.h"

// definitions
#define XMAX 640
#define YMAX 480

// prototypes
void gray1(int xmax, int ymax);
void gray2(int xmax, int ymax);

// global variable
char picture[YMAX][XMAX]; // global variable

// main
int main ()
   {
   srand(time(NULL)); // seed the random number generator
   int x, y;
   float sum;

   for ( y = 0; y < YMAX; y++) for (x = 0; x < XMAX; x++) picture[y][x] = 0;
   gray1(XMAX, YMAX); // first function
   sum = 0;
   for ( y = 0; y < YMAX; y++) for (x = 0; x < XMAX; x++) sum += picture[y][x];
   cout << endl << "average value for gray1() is " << sum / (XMAX * YMAX) << endl;

   for (y = 0; y < YMAX; y++) for (x = 0; x < XMAX; x++) picture[y][x] = 0;
   gray2(XMAX, YMAX); // first function
   sum = 0;
   for (y = 0; y < YMAX; y++) for (x = 0; x < XMAX; x++) sum += picture[y][x];
   cout << endl << "average value for gray2() is " << sum / (XMAX * YMAX) << endl;

   } // end main()

// functions
void gray1(int xmax, int ymax)
   {
   for (int y = 0; y < ymax; y++)
      for (int x = 0; x < xmax; x++)
         if (rand()%2) picture[y][x] = 1; // black
   } // end gray1()
   
void gray2(int xmax, int ymax)
   {
   for (int n = 0; n < xmax*ymax/2; n++)
      {
      int x = rand() % xmax; int y = rand() % ymax;
      picture[y][x] = 1; // black
      }
   } // end gray2()

// Copyright 1998 Norman Wittels

ernie.WPI.EDU> g++ exam04_01.C

ernie.WPI.EDU> a.out

average value for gray1() is 0.500615

average value for gray2() is 0.393623

ernie.WPI.EDU>