Segmentation fault (core dumped) in file handling in c -

i new stack overflow please forgive me if have disobeyed rules. trying run code

#include<stdio.h> #include<stdlib.h> int o[100][100]; int a[100][100]; int b[5]; int h,w; int alpha; int min() {     int i,m=b[0],k=0;     for(i=1;i<5;i++)     {        if(b[i]<m)        {            m=b[i];            k=i;         }      }      return k;  }  int set(int j,int k)  {      b[0]=a[j][k];      b[1]=((j-1)>=0)?a[j-1][k]:12000;      b[2]=((k-1)>=0)?a[j][k-1]:12000;      b[3]=((k+1)<w)?a[j][k+1]:12000;      b[4]=((j+1)<h)?a[j+1][k]:12000;      int dir=min();      int j1,k1;      if(dir==1)      {           j1=j-1;           k1=k;      }      else if(dir==2)      {           j1=j;           k1=k-1;       }       else if(dir==3)       {          j1=j;          k1=k+1;       }       else if(dir==4)       {          j1=j+1;          k1=k;       }       if(o[j1][k1]==-1 && dir!=0)           set(j1,k1);       if(dir==0)       {           o[j][k]=alpha;           alpha++;        }       else       {           o[j][k]=o[j1][k1];        } } int main() {     printf("2");     file* f1=fopen("b-small-practice(1).in","r");     file* f2=fopen("otput.out","w");     if(f1==null)         printf("error in f1\n");     if(f2==null)         printf("error in f2\n");     int i,j,k;     int t,dir;     fscanf(f1,"%d",&t);     for(i=1;i<=t;i++)     {         alpha=97;         fscanf(f1,"%d %d",&h,&w);         for(j=0;j<h;j++)         {             for(k=0;k<w;k++)             {                 fscanf(f1,"%d",&dir);                 a[j][k]=dir;                 o[j][k]=-1;             }         }         for(j=0;j<h;j++)         {             for(k=0;k<w;k++)             {                 if(o[j][k]==-1)                 {                     set(j,k);                  }              }          }          fprintf(f2,"case #%d:\n",i);          for(j=0;j<h;j++)          {             for(k=0;k<w;k++)             {                 fprintf(f2,"%c ",o[j][k]);             }             fprintf(f2,"\n");           }     }     fclose(f1);     fclose(f2); } 

when ran code without file operation ran when used file gave segmentation fault. had problem many times. please me in identifying problem in code can never repeat mistake. in advance

a segmentation fault program trying access memory not allowed to.

you error on line b[4]=((j+1)<h)?a[j+1][k]:12000; assume either j+1 or k exceeds bounds of a array.

i not debug you, since taht want learn become programmer, , part of becoming debugging.

start inserting printouts of variables, e.g. in beginning of set function. in addition, should check input file within legal range.

as general programming tip; try work on readability of code. readability more important making clever code. compiler of times optimize code, , more clever programmer. trying clever can give opposite effect, compiler not recognize pattern , not optimize you.