The subscripting should be here:
Code:
strncpy(students[i]->firstName, input_string, MAX_SIZE);
Those other lines you added are meaningless.
Also, since you changed the prototype:
Code:
int get_info(struct student_data *studentPtr )
int get_info( struct student_data students[MAX_STUDENTS] )
You won't be able to use indirect notation (->); so you might as well change it back (as I said, with structs, *studentPtr could be a single struct or an array of structs, you don't need students[MAX]). The only place the subscripting is relevant is the red bit, above.