bus error

[ssteches]

i keep getting a bus error but i don't know why

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


    typedef struct data
    {
      char student[10];
      int scores[4];
      char alp_grd; 
      float avg_grd;
    } dat_t;


  void avg_score (dat_t student_t[13]);
  void letter_grd (dat_t student_t[13]);
  void results(dat_t student_t[13]);
  void sort_avg(dat_t student_t[13]);
int main(void)
{
  dat_t student_t[13];
  FILE *fp;
  int s=0;
  int n=0;


  printf("\n Reading the name file\n");
  fp = fopen("student.dat", "r");
  
  for(n=0;n<13;n++)
  {
    fscanf(fp,"%s",&student_t[n].student);
  }
  fclose(fp);
  
  printf("\n Reading the scores file\n");
  fp = fopen("scores.dat", "r");
 


  for(n=0;n<13;n++)
  {
    for(s=0;s<4;s++)
    {
      fscanf(fp,"%d",&student_t[n].scores[s]);
    }
  }
  fclose(fp);


 avg_score(student_t);


 letter_grd(student_t);


 sort_avg (student_t);


 results(student_t);


 return(0);
}


 
 void avg_score(dat_t student_t[13])
{
  int n,s;
  float sum = 0, average = 0;
  
  for(n=0;n<13;n++)
  {
    for(s=0;s<4;s++)
    { 
      sum = sum + student_t[n].scores[s];
    }
    average = sum / 4;
    student_t[n].avg_grd = average;
    sum = 0;
  }
}


void letter_grd (dat_t student_t[13])
{
  int s;


  for(s=0;s<13;s++)
  {
    if(student_t[s].avg_grd>=90)
      student_t[s].alp_grd = 'A';
    else if((student_t[s].avg_grd>=80)&&(student_t[s].avg_grd<90))
      student_t[s].alp_grd = 'B';
    else if((student_t[s].avg_grd>=70)&&(student_t[s].avg_grd<80))
      student_t[s].alp_grd = 'C';
    else if((student_t[s].avg_grd>=65)&&(student_t[s].avg_grd<70))
      student_t[s].alp_grd = 'D';
    else if(student_t[s].avg_grd<65)
      student_t[s].alp_grd = 'F';
  }
}


void results(dat_t student_t[13])
{
  int s,n;


  printf("\n\nName\t Exam1   Exam2   Exam3   Exam4    Averag  letter Grade\n\n");


  for(s=0;s<13;s++)
  {
    printf("%-s\t ", student_t[s].student);
    for(n=0;n<4;n++)
    {
      printf("%-2d\t ", student_t[s].scores[n]);
    }
    printf(" %-3.2f\t\t%-c \n", student_t[s].avg_grd,student_t[s].alp_grd);
  }
}


void sort_avg(dat_t student_t[13])
{
  dat_t temp;
  int i,j,min;


  for ( i = 0 ; i < 12 ; i++ )
  {
    for ( j = i+1 ; 13-i ; j++ ) 
    {
      if (student_t[i].avg_grd < student_t[j].avg_grd)
      {
        temp = student_t[j];
        student_t[j] = student_t[i];
        student_t[i] = temp;
      }
    }  
  }  
}

[Adak]

That's a substitution sort, but this part is incorrect:

 for ( j = i+1 ; 13-i ; j++ )      //13-i??

Because 13-i will always resolve to TRUE (non-zero), so the loop will never quit.