Expert: vijayan - 12/4/2008

Question
hi
in this code below in the line that i have signed i don't know why it just print the value x=1 and y=2 befor running BUG function though i have persisted to change the value of x and y in the 'if' or 'else'in BUG function
plz..i need your help about this problem:-(


#include <stdlib.h>
#include <time.h>
#include<string.h>
#include<stdio.h>

void BUG(int x,int y);

int stor1[50],stor2[50],mark[40][20],count=0,m,n;

void main()
{
  int j=0,i=0,w=0,t=0,x=0,y=0;
  printf("Enter m&n:1<m<41,1<n<21\n");
  scanf("%d%d",&m,&n);
  
  for(i=1;i<=m;i++)
     for(j=1;j<=n;j++)
        mark[i][j]=0;

     m=m+1;
     n=n+1;

     x=m/2;
     y=n/2;

  i=0;
  for(j=0;j<=n;j++)
      mark[i][j]='#';

    i=m;
  for(j=0;j<=n;j++)
     mark[i][j]='#';
  j=0;
  for(i=0;i<=m;i++)
     mark[i][j]='#';
  j=n;
  for(i=0;i<=m;i++)
     mark[i][j]='#';

  

  stor1[0]=m/2;
   stor2[0]=n/2;

   mark[x][y]=1;

  t=mark[i][j];
  do{

      printf("BEFOR ENTERING LOOPx=%d,y=%d\n\n",x,y);//*<----------printing the same value for x and y evrey time

     BUG(x,y);

     for(i=1;i<=m-1;i++)
          for(j=1;j<=n-1;j++){
             
             if(t==0)
               w=0;
             else{
               w=1;
             }
          }
           
          
       }while(w!=1);

          printf("Time=%d\n",count);
}
void BUG(int x,int y){



  int a=0,b=0;      

  int k = 1 + int( 8.0 * ( rand()  /  ( RAND_MAX + 1.0 ) ) ) ;

         

         a++;
       b++;

         printf("Direction=%d\n",k);

       if(k==1){
          x=x-1;
          y=y+1;
          count++;
       }
       else if(k==2){
          y=y+1;
          count++;
       }
       else if(k==3){
          x=x+1;
          y=y+1;
          count++;
       }
       else if(k==4){
          x=x+1;
          count++;
       }
       else if(k==5){
          x=x+1;
          y=y-1;
          count++;
       }
       else if(k==6){
          y=y-1;
          count++;
       }
       else if(k==7){
          x=x-1;
          y=y-1;
          count++;
       }
       else if(k==8){
          x=x-1;
          count++;

       }

  
       
      
       stor1[a]=x;
       stor2[b]=y;



       

       if(mark[x][y]=='#'){



          a=a-1;
          b=b-1;

          x=stor1[a];
          y=stor2[b];

       }
         else{


       mark[x][y]=1;

       }
         

}

thanx
Bita

Answer
   void BUG( int x, int y ) ;

function BUG takes the parameters by value. what bug gets are copies of x and y. changes to these copies do not affect the x and y in main.

modify BUG to take the parameters by reference instead of by value:

   void BUG( int& x, int& y ) ;



or, if you are programming in pure C, take the parameters by address (pointers):

   void BUG( int* x, int* y ) ;

in this case, call BUG like this: BUG( &x, &y ) ;

and in BUG, use *x, *y instead of x, y.