Having a fatal error code - corrupted heap

Question

New picture from an external compiler.. the exit code is ok?

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This is the full code. I'm having a trouble program blows away after printing the wanted output to the screen. I guess it's a problem with the way I allocated memory for the array of structs, and the .name field of each struct in a for loop.

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

#define MAX_NAME_LEN 50

typedef struct stud
{
char *name;
int marks[4];
float avg;
}student;


student* Create_Class(int);
void Avg_Mark(student*);
void Print_One(student*);
void printExcellent(student*);

void main()
{
int size, i;
student *arr, *newArr;
printf("\nEnter the number of students: ");
scanf_s("%d", &size);
newArr = Create_Class(&size);
for (i = 0; i < size; i++)
{
    printExcellent(newArr+i);
}
for (i=0;i<size;i++) free(newArr[i].name);
free(newArr);
_getch();
}

student* Create_Class(int size)
{
student *p;
char str[MAX_NAME_LEN];
int i, j;
p = (student*)calloc(size , sizeof(student));
if (!p)
{
    printf("Memory allocation failure.");
    exit(1);
}

for (i = 0; i < size; i++)
{
    printf("Enter your name: ");
    rewind(stdin);
    gets(str);
    p[i].name = (char*)calloc(strlen(str)+1,sizeof(char));
    if (!(p[i].name))
    {
        printf("Memory allocation error!");
        exit(1);
    }
    strcpy_s(p[i].name,50,str);
    printf("Enter your marks: ");
    for (j = 0; j < 4; j++)
    {
        scanf_s("%d", &p[i].marks[j]);
    }
    Avg_Mark(p + i);
}
return p;
}


void Avg_Mark(student* s)
{
int i, sum=0;
for (i = 0; i < 4; i++)
    sum += s->marks[i];
s->avg = (float)sum / 4;
}


void Print_One(student* s)
{
printf("The average of %s is %.1f\n", s->name, s->avg);
}

void printExcellent(student* s)
{
if ((s->avg) > 85)
    Print_One(s);
}

Answer 1

Gonna point out everything fishy I see for you:

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

#define MAX_NAME_LEN 50

typedef struct stud
{
    char *name;
    int marks[4];
    float avg;
}student;


student* Create_Class(int);
void Avg_Mark(student*);
void Print_One(student*);
void printExcellent(student*);

void main()
{
    int size, i;
    student *arr, *newArr;
    printf("\nEnter the number of students: ");
    scanf_s("%d", &size);

    // This is wrong. Remove the &...
    newArr = Create_Class(&size);

    for (i = 0; i < size; i++)
    {
        printExcellent(newArr+i);
    }
    for (i=0;i<size;i++) free(newArr[i].name);
    free(newArr);
    _getch();
}

student* Create_Class(int size)
{
    student *p;
    char str[MAX_NAME_LEN];
    int i, j;

    // Consider checking size for a sane value.

    // Ok, allocate an array of students.
    p = (student*)calloc(size , sizeof(student));
    if (!p)
    {
        printf("Memory allocation failure.");
        exit(1);
    }

    for (i = 0; i < size; i++)
    {
        printf("Enter your name: ");

        // These 2 lines scare the heck out of me.  I'd really do this differently.
        // gets is the devil and the see:
        // https://stackoverflow.com/questions/20052657/reversing-stdin-in-c
        // for why this may not work well.

        rewind(stdin);
        gets(str);

        // What if str is not a terminated string?  Then 1 char of 0?  Guess this is ok.  Hope it doesn't overflow on the copy below though (consider fixed max size and not using a temporary)
        p[i].name = (char*)calloc(strlen(str)+1,sizeof(char));
        if (!(p[i].name))
        {
            printf("Memory allocation error!");
            exit(1);
        }
        // Do a fast copy of up to 50 chars. I'd really want to verify this output to be sure it works. 
        strcpy_s(p[i].name,50,str);
        printf("Enter your marks: ");
        for (j = 0; j < 4; j++)
        {
            // Hope this inputs the way you want.
            scanf_s("%d", &p[i].marks[j]);
        }

        // This should work, but I prefer more explicit pointers.
        Avg_Mark(p + i);
    }

    return p;
}


void Avg_Mark(student* s)
{
    // What if s is Null?

    int i, sum=0;

    // 4 is a magic number.  Make this a constant.
    for (i = 0; i < 4; i++)
        sum += s->marks[i];

    // This won't be as accurate as you want.  Consider an integer solution.
    s->avg = (float)sum / 4;
}


void Print_One(student* s)
{
    // What if s is Null?  What about s->name?
    printf("The average of %s is %.1f\n", s->name, s->avg);
}

void printExcellent(student* s)
{
    // What if s is Null?
    if ((s->avg) > 85)
        Print_One(s);
}

Note: While going through this code, I did not see any "red flags" except for the & on the size and perhaps the gets/rewind calls. I'd still add null asserts to your functions and also walk through it with a debugger to be sure that everything is as you expect. Honestly, there is enough going on here that I'd prefer the debugger help to my quick trace of the code while I was writing comments.

---

Update

If I change all your scanf_s to scanf() calls, replace your gets() / rewind() calls to a simple scanf("%s", str) call, and change your funky strcpy_s() function to a simpler strcpy() or strncpy() call, your program does not seem to crash for me. My money is that the strcpy_s() call is corrupting RAM while doing its "fast" copy.