question about Insertion sort

Hello... I have a question This is my code for Insertion sort...
But it doesn't work... I don't know What the problem is...
The output is
-30000
1
2
3

but it should be
1
2
3
4

I need help... Thanks in advance

#include <stdio.h>

#define MAXINT 30000

typedef struct {
int stud_id;
char name[10];
char grade[4];
}student;


void Insertion(int , student* );

void main()
{
int i;
student std[5] =
{{1000, "xxxxxx ", "A+ "},
{4, "aaaaaaa", "A+"},
{3, "bbbbbb", "A0"},
{1, "ccccccc", "A0"},
{2, "ddddddd", "B0"}};

Insertion(5, std);

for(i = 1; i < 5; i++)
printf("%d\n", (std + i)->stud_id);

}

void Insertion(int n, student* s)
{
int i, j, r;

s->stud_id = -MAXINT;

for(i = 2; i <= n; i++)
{
j = i - 1;
r = (s + i)->stud_id;
while(r < (s + j)->stud_id)
{
(s + j + 1)->stud_id = (s + j)
->stud_id;
j = j - 1;
}
(s + j + 1)->stud_id = r;
}
}

The loop runs one time more than it should, because of the error in the the loop condition. It should be i < n instead of i <= n.

When n is 5 (with your test data), you're reading one element pasted the end of the array 's'.

Happy hacking,
Jonas

Your reply is really helpful... Thank you...