c - Segmentation fault error for a matrix assignment -

this code creation of grid similar of game "mines":

#include <stdio.h> #include <stdlib.h>  int main(){      int nr, nc, ** mtx, i, j;      //matrix costruction      file * instr;      instr = fopen("brasa.dat","r");      if(instr == null){          printf("\nproblem while opening file.\n");          return 1;      }      fscanf(instr, "%d%d", &nr, &nc);      mtx = (int**) malloc(nr * sizeof(int*));     if(mtx == null){         printf("\nmemory allocation error.\n");         return 1;     }     else{         for(i = 0; < nr; i++)                   mtx[i] = (int*) malloc(nc * sizeof(int));             if(mtx[i] == null){                 printf("\nmemory allocation error.\n");                 return 1;             }     }      //filling matrix      for(i = 0; < nr; i++){         for(j = 0; j < nc; j++)             mtx[i][j] = 0;     }      while(!feof(instr)){         fscanf(instr,"%d %d",&i,&j);         mtx[i][j] = 9;     }      fclose(instr);      for(i = 0; < nr; i++){         for(j = 0; j < nc; j++){              if(i == 0){                 if(j == 0){                     if(mtx[i][j+1] > 8)                         mtx[i][j]++;                     else if(mtx[i+1][j] > 8)                         mtx[i][j]++;                     else if(mtx[i+1][j+1] > 8)                         mtx[i][j]++;                 }                 else if(j == nc-1){                     if(mtx[i][j-1] > 8)                         mtx[i][j]++;                     else if(mtx[i+1][j-1] > 8)                         mtx[i][j]++;                     else if(mtx[i+1][j] > 8)                         mtx[i][j]++;                 }                 else{                     if(mtx[i][j-1] > 8)                         mtx[i][j]++;                     else if(mtx[i][j+1] > 8)                         mtx[i][j]++;                     else if(mtx[i+1][j-1] > 8)                         mtx[i][j]++;                     else if(mtx[i+1][j] > 8)                         mtx[i][j]++;                     else if(mtx[i+1][j+1] > 8)                         mtx[i][j]++;                 }             }             else if(i == nr-1){                 if(j == 0){                     if(mtx[i+1][j] > 8)                         mtx[i][j]++;                     else if(mtx[i+1][j+1] > 8)                         mtx[i][j]++;                     else if(mtx[i][j+1] > 8)                         mtx[i][j]++;                 }                 else if(j == nc-1){                     if(mtx[i][j-1] > 8)                         mtx[i][j]++;                     else if(mtx[i+1][j-1] > 8)                         mtx[i][j]++;                     else if(mtx[i+1][j] > 8)                         mtx[i][j]++;                  }                    else{                     if(mtx[i][j-1] > 8)                         mtx[i][j]++;                     else if(mtx[i+1][j-1] > 8)                         mtx[i][j]++;                     else if(mtx[i+1][j] > 8)                         mtx[i][j]++;                     else if(mtx[i+1][j+1] > 8)                         mtx[i][j]++;                     else if(mtx[i][j+1] > 8)                         mtx[i][j]++;                 }             }             else if(j == 0){                 if(mtx[i+1][j] > 8)                     mtx[i][j]++;                 else if(mtx[i+1][j+1] > 8)                     mtx[i][j]++;                 else if(mtx[i][j+1] > 8)                     mtx[i][j]++;                 else if(mtx[i-1][j+1] > 8)                     mtx[i][j]++;                 else if(mtx[i-1][j] > 8)                     mtx[i][j]++;             }             else if(j == nc-1){                 if(mtx[i+1][j] > 8)                     mtx[i][j]++;                 else if(mtx[i+1][j-1] > 8)                     mtx[i][j]++;                 else if(mtx[i][j-1] > 8)                     mtx[i][j]++;                 else if(mtx[i-1][j-1] > 8)                     mtx[i][j]++;                 else if(mtx[i-1][j] > 8)                     mtx[i][j]++;              }                else{                 if(mtx[i-1][j-1] > 8)                     mtx[i][j]++;                 else if(mtx[i][j-1] > 8)                     mtx[i][j]++;                 else if(mtx[i+1][j-1] > 8)                     mtx[i][j]++;                 else if(mtx[i+1][j] > 8)                     mtx[i][j]++;                 else if(mtx[i+1][j+1] > 8)                     mtx[i][j]++;                 else if(mtx[i][j+1] > 8)                     mtx[i][j]++;                 else if(mtx[i-1][j+1] > 8)                     mtx[i][j]++;                 else if(mtx[i-1][j] > 8)                     mtx[i][j]++;             }             if(mtx[i][j] > 8)                 printf("*\t");             else                 printf("%d\t", mtx[i][j]);         }     }      free(mtx);     return 0; } 

during execution of program appears segmentation fault. doing several tests noticed problem should between line 85 , line 158. can me?

you have invalid access

        // ...         else if(i == nr-1){               // nr - 1             if(j == 0){                 // ...             }             else if(j == nc-1){                 // ...                 else if(mtx[i+1][j] > 8)  // + 1 nr (invalid access)                 // ...