Program prints garbage values in weird places (C) [closed] - c

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When I'm running the program, the 2nd and the 3rd values being printed are garbage values, and I don't know why. I think it should be the numbers I've entered.
The code:
int main()
{
int a = 0, b = 0;
int * students = NULL;
int * size = &a;
int * studentscount = &b;
func1(students, size, studentscount);
return 0;
}
#include "Source.h"
int checkAllocation(void * ptr)
{
if (ptr == NULL)
return 1;
return 0;
}
int * doubleArr(int *arr, int size)
{
int * newArr = (int*)malloc(size * sizeof(int));
checkAllocation(newArr);
for (int i = 0; i < size; i++)
newArr[i] = arr[i];
size *= 2;
newArr = (int*)realloc(newArr, size);
checkAllocation(newArr);
free(arr);
return (newArr);
}
void func1(int *students, int *size, int *studentscount)
{
int num;
students = (int *)malloc(sizeof(int) * 2);
checkAllocation(students);
*(studentscount) = 0;
*(size) = 2;
printf("Enter students, to end enter a negative number.\n");
do
{
printf("Enter student number %d: ", *(studentscount)+1);
scanf("%d", &num);
if (num >= 0)
{
*(students + *(studentscount)) = num;
*(studentscount) += 1;
}
if (*(studentscount) == (*size))
{
students = doubleArr(students, *(size));
*(size) *= 2;
}
} while (num >= 0);
printf("******************\nArray size: %d\nNumber of students: %d\n******************\n", *(size), *(studentscount));
for (int i = 0; i < *(studentscount); i++)
printf("student #%d: %d\n", i + 1, *(students + i));
free(students);
}
Any suggestions to make the code print the values I entered and not the garbage values?

Answer 1

There are some issues you should probably work on, but the reason for garbage is very likely statement realloc(newArr, size), which considers only the count but not the size of datatype int. Hence, instead of doubling the array size, you are actually decreasing it; Consequently, realloc might give you back a different memory block where only portions of the previous one has been taken over; or some parts of the memory you have written values to have gone invalid. Anyway, you have a good chance here to loose your entered values. So - as pointed out by bluepixy, statement realloc(newArr, size*sizeof(int)) should solve the main problem.
Note further that statement realloc, when allocating memory at a different place, takes over the content of the former memory block and (in this case) frees the former block (cf. cppreference of realloc). So there is no need to transfer the data manually, there is particularly no need to first malloc and then realloc, and there is consequently no need for a separate free at the end. So the code of doubleArr could actually look like the following.
int * doubleArr(int *arr, int size) {
return realloc(arr,size*2*sizeof(int));
}