#include <stdio.h>

int main (void)
{
  int i, j;
  FILE* fp;

  int tmp[][5]={
    {1, 2, 3, 4, 5},
    {3, 5, 6, 7, 8},
    {8, 4, 2, 5, 7},
    {5, 4, 6, 7, 6},
  };

  fp = fopen ("data.txt", "w") ;

  for (i = 0; i < sizeof(tmp) / sizeof(tmp[0]); i++) {
    for (j = 0; j < sizeof(tmp[0]) / sizeof(tmp[0][0]); j++) 
      fprintf(fp, "%d", tmp[i][j]);
    fputs("\n", fp);
  }  

  fclose (fp);

  return 0 ;
}

Segmentation fault