Thread: some kinda crash

  1. 01-14-2007 #1
    ch4
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    Can anyone explain why this happen each time i run my prog?
    Code:
    #include<stdio.h>
#include<stdlib.h>
int **B;
int pinfun(int i,int x,int y ,int n,int **B);
int main (void){
    int m,j,k;
    scanf("%d",&m);
    B=malloc((m+200) * sizeof(int *));
    for(j=0;j<m;j++){
                     B[j]=malloc(m*sizeof(int));
                     }
    for(j=0;j<m;j++){
                     for(k=0;k<m;k++){
                                      *(*(B+j)+k)=0;
                                      }
                     }
                     
    pinfun(1,0,0,m,B);
    for(j=0;j<m;j++){
                     for(k=0;k<m;k++){
                                      printf("%d    ",B[j][k]);
                                      }
                     printf("\n\n");
                     }
getchar();
getchar();
}

int pinfun(int i,int x,int y,int n,int **B){
  
    if(i<=n*n){            
              if((pinfun(i+1,x+3,y,n,B)==1)&&(y>=0)&&(y<=n)&&(x>=0)&&(x<=n)&&((B[x][y])==0)){
                                                        B[x][y]=i;
                                                         return 1;
                                                        }
             if((pinfun(i+1,x-3,y,n,B)==1)&&(y>=0)&&(y<=n)&&(x<=n)&&(x>=0)&&(B[x][y]==0)){
                                                        B[x][y]=i;
                                                         return 1;
                                                        }
             if((pinfun(i+1,x,y+3,n,B)==1)&&(y>=0)&&(y<=n)&&(x<=n)&&(x>=0)&&(B[x][y]==0)){
                                                        B[x][y]=i;printf("%d\n",i); 
                                                         return 1;
                                                        }
             if((pinfun(i+1,x,y-3,n,B)==1)&&(y>=0)&&(y<=n)&&(x<=n)&&(x>=0)&&(B[x][y]==0)){
                                                        B[x][y]=i;
                                                         return 1;
                                                        }
            if((pinfun(i+1,x-2,y-2,n,B)==1)&&(y>=0)&&(y<=n)&&(x<=n)&&(x>=0)&&(B[x][y]==0)){
                                                        B[x][y]=i;
                                                         return 1;
                                                        }
            if((pinfun(i+1,x+2,y+2,n,B)==1)&&(y>=0)&&(y<=n)&&(x<=n)&&(x>=0)&&(B[x][y]==0)){
                                                        B[x][y]=i;
                                                         return 1;
                                                        }
            if((pinfun(i+1,x+2,y-2,n,B)==1)&&(y>=0)&&(y<=n)&&(x<=n)&&(x>=0)&&(B[x][y]==0)){
                                                        B[x][y]=i;
                                                         return 1;
                                                        }
            if((pinfun(i+1,x-2,y+2,n,B)==1)&&(y>=0)&&(y<=n)&&(x<=n)&&(x>=0)&&(B[x][y]==0)){
                                                        B[x][y]=i;
                                                         return 1;
                                                        }
            if((y<0)||(y>n)||(x>n)||(x<0)||B[x][y]!=0){
                                                       
                                                       return 0;
                                                                }

                                
         } 
       else{
            B[x][y]=i;
            return 1;
            }
    }
    For example if given number is 5
    i expect an output like this

    1 19 16 4 20
    14 24 8 11 23
    17 5 21 18 6
    2 10 15 3 9
    13 25 7 12 22

    And my output is:

    1 0 0 0 0
    0 0 0 0 0
    0 0 0 0 0
    2 0 0 0 0
    0 0 0 0 0

    The overal problem is to fill a square with numbers such as it's size
    1 placed allways in the first position
    2 can be placed two boxes vertically or horizontaly or one box across from 1
    So each number should be placed two boxes vertically or horizontaly or one box across from the last.
  2. 01-14-2007 #2
    Salem
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    Split from http://cboard.cprogramming.com/showthread.php?t=87398
    Please don't hijack threads with your own questions.
    If you dance barefoot on the broken glass of undefined behaviour, you've got to expect the occasional cut.
    If at first you don't succeed, try writing your phone number on the exam paper.
  3. 01-14-2007 #3
    Deckard
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    pinfun() keeps calling itself until i > n*n, incrementing x by three each time. By the time i is larger than n*n, x is larger than the number your user entered. That becomes a factor the first time you hit this:
    Code:
    else {
   B[x][y]=i;
   return 1;
}
    B[x] is 0x00000000. When you try to dereference that address, you get a segmentation fault. For what it's worth, in your example of the user entering "5", the value of x is 72 when you attempt to use B (or, B[72] when you only allocated B[0] through B[4]).

    I could probably be more help if I had a better idea of what you were trying to accomplish.
    Last edited by Deckard; 01-14-2007 at 08:01 AM. Reason: post-caffeine terminology correction
    Jason Deckard
  4. 01-14-2007 #4
    ch4
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    Ok Salem
    I will be more carefull in the future.

    Thanks
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