Issues with printing structs in C - arrays

Question

I'm incredibly new to this and have a school assignment I have to write a gradebook program that uses a custom struct to hold student IDs and grades. I have been trying unsuccessfully for days to figure out why it will not print properly, or when it does print (after a lot of shifting things around) it only prints the second set of input.
The gradebook.h section is the custom structure.
// gradebook.h
struct gradeID
{
int id;
char grades[25];
};
// Gradebook.h is a header file to define
// a global structure.
#include "gradebook.h"
#include <stdio.h>
#include <stdlib.h>
void sort(struct gradeID *, int);
int main(void)
{
// Variables and structure definitions
int ctr;
char contInput;
int i;
struct gradeID grade;
struct gradeID *identifier;
int *temps;
// Allocates 10 integers worth of memory for the program to use.
// If there is not enough memory, the program will print an error
// statement and terminate the program.
temps = (int *) malloc(10 * sizeof(int));
if (temps == 0)
{
printf("Not enough memory!\n");
exit(1);
}
// Prints basic instructions for the program
printf("\t\tGradebook Recorder\n");
printf("Input student IDs and grades.\n");
printf("These will be sorted by ID and printed.\n");
/* Creates a for loop that will continue until the program
hits the designated number of array elements. For the sake
of expediency, I have set this amount to 10, but it can be
changed as necessary.*/
for(i = 0; i < 10; i++)
{
printf("Input student ID:\n");
scanf(" %d", &grade.id);
printf("Input grade:\n");
scanf(" %s", grade.grades);
// This allows early exit of the program
printf("Do you have more grades to enter?\n");
printf("Y/N\n");
scanf(" %c", &contInput);
if(contInput == 'N' || contInput == 'n')
{
printf("Finalizing and printing input-\n\n");
break;
}
ctr++;
}
printf("Grades Sorted by Student ID:\n\n");
printf("\tStudent ID: Student Grade: \n");
for(i = 0; i < ctr; i++)
{
printf("\t%d", grade.id );
printf("\t%s", grade.grades);
}
identifier[i] = grade;
return(0);
free(temps);
}
void sort(struct gradeID identifier[], int counter)
{
int inner;
int outer;
struct gradeID temp;
// Loops for sorting
for(outer = 0; outer < counter - 1; ++outer)
{
for(inner = outer + 1; inner < counter; ++inner)
{
if(identifier[inner].id < identifier[outer].id)
{
temp = identifier[inner];
identifier[inner] = identifier[outer];
identifier[outer] = temp;
}
}
}
return;
}

Answer 1

The pointer identifier is uninitialized
struct gradeID *identifier;
So this statement
identifier[i] = grade;
independent on the value of i invokes undefined behavior.
In this for loop
for(i = 0; i < 10; i++)
{
printf("Input student ID:\n");
scanf(" %d", &grade.id);
printf("Input grade:\n");
scanf(" %s", grade.grades);
// This allows early exit of the program
printf("Do you have more grades to enter?\n");
printf("Y/N\n");
scanf(" %c", &contInput);
if(contInput == 'N' || contInput == 'n')
{
printf("Finalizing and printing input-\n\n");
break;
}
ctr++;
}
you are entering new data in the same object grade of the structure type. So the new data overrides the previous data stored in the object.
Moreover the variable ctr was not initialized
int ctr;
So this statement in the above for loop
ctr++;
also invokes undefined behavior.
The variable temps that points to a dynamically allocated array
temps = (int *) malloc(10 * sizeof(int));
is not used.
This statement
free(temps);
never gets the control because before it there is the return statement
return(0);
free(temps);
What you need is to define an array of the type struct gradeID as for example
struct gradeID grades[10];
and fill it with values.