Why does code not work after using fopen() command - pointers

Question

I created FILE *ptr to read a file, and after I declare ptr =fopen("file_name.txt", "r");
none of my code written afterwards will work.
BELOW IS SOME OF THE ACTUAL CODE
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <ctype.h>
#define MAXFILE 30
#define MAX 50
typedef struct Student
{
int stdid;
char *fname;
char *lname;
int day;
int month;
int year;
}Student;
typedef struct Course
{
char *cid;
char *cname;
float credit;
}Course;
typedef struct Enrollment
{
int stdid;
int cid;
char *semester;
float score;
}Enrollment;
int main()
{
char stud[MAXFILE], courses[MAXFILE], enroll[MAXFILE];
printf("TESTING1");
scanf("%s %s %s",stud,courses,enroll);
int studnum,coursenum,enrollnum;
FILE *st, *cou, *enr;
st = fopen("stud","r");
cou = fopen("courses","r");
enr = fopen("enroll","r");
printf("TESTING2");
if(st==NULL || cou == NULL || enr== NULL)
{
printf("unable to open file\n");
exit(1);
}
fscanf(st,"%d",&studnum);
Student *students = (Student*)(malloc(sizeof(Student) * studnum));
for(int i =0; i<studnum;i++)
{
char ftemp[MAX],ltemp[MAX];
int fir, las;
fscanf(st,"%d %s %s %d %d %d",&students[i].stdid, ftemp, ltemp, &students[i].day, &students[i].month, &students[i].year);
fir = strlen(ftemp)+1;
las = strlen(ltemp)+1;
strcpy(students[i].fname,ftemp);
strcpy(students[i].lname,ltemp);
students[i].fname = malloc(fir * sizeof(char));
students[i].lname = malloc(las * sizeof(char));
strcpy(students[i].fname,ftemp);
strcpy(students[i].lname,ltemp);
}
//reading the students.txt file and filling out Student type array with data;
printf("TESTING3");
fscanf(cou,"%d",&coursenum);
Course *course = (Course*)(malloc(sizeof(Course)*coursenum));
for(int i =0; i<coursenum;i++)
{
char cidtemp[MAX], cntemp[MAX];
int tempcid, tempcn;
fscanf(cou,"%s %s %f",cidtemp, cntemp, &course[i].credit);
tempcid = strlen(cidtemp)+1;
tempcn = strlen(cntemp)+1;
course[i].cid = malloc(tempcid*sizeof(char));
course[i].cname = malloc(tempcn * sizeof(char));
strcpy(course[i].cid,cidtemp);
strcpy(course[i].cname, cntemp);
}
//reading the couses.txt file and filling out an array of type Course with the data
printf("TESTING4");
fscanf(enr,"%d",&enrollnum);
Enrollment *enrollment = (Enrollment*)(malloc(sizeof(Enrollment)*enrollnum));
for(int i =0; i<enrollnum; i++)
{
int stdid;
int cid;
char *semester;
float score;
char semest[MAX];
int semtemp;
fscanf(enr,"%d %d %s %f",&enrollment[i].stdid, &enrollment[i].cid, semest, &enrollment[i].score);
semtemp = strlen(semest)+1;
enrollment[i].semester = malloc(semtemp * sizeof(char));
strcpy(enrollment[i].semester, semest);
printf("%d\t%d\t%s\t%.0f \n", enrollment[i].stdid, enrollment[i].cid, enrollment[i].semester, enrollment[i].score);
}
//reading the enrollment files and fill out at array of type Enrollment
//testing new arrays
printf("%d", enrollnum);
for(int i = 0; i<enrollnum; i ++)
{
printf("%d\t%d\t%s\t%.0f \n", enrollment[i].stdid, enrollment[i].cid, enrollment[i].semester, enrollment[i].score);
}
fclose(st);
fclose(cou);
fclose(enr);
for(int i =0; i < studnum;i++)
{
free(students[i].fname);
free(students[i].lname);
}
free(students);
for(int i =0; i < coursenum;i++)
{
free(course[i].cid);
free(course[i].cname);
}
free(course);
for(int i =0; i < enrollnum;i++)
{
free(enrollment[i].semester);
}
free(enrollment);
return 0;
}