2D Array elements changing after they are set - c

Question

The program below is meant to print a square grid of integers based on the dimension which is inputted by the user (as part of the harvard cs50 course on edx).
The array is being initialized correctly, but when it comes to printing it out, the last column always prints incorrectly. I tried debugging by putting 2 printf statements in the innermost for loop of the init() function.
It seems that after the outermost loop runs once, the entry in the last column gets decremented by one, although it was correct just before this.
Why is this happening? Shouldn't it print correctly?
#include <stdio.h>
main()
{
void init(int dim, int arr[dim-1][dim-1]);
int dim;
printf("Enter board dimension(max 10): ");
scanf("%d", &dim);
int arr[dim-1][dim-1];
init(dim, arr);
int i,j;
for(i=0;i<dim;i++)
{
for(j=0;j<dim;j++)
{
printf("%2d ",arr[i][j]);
}
printf("\n");
}
}
void init(int dim, int arr[dim-1][dim-1])
{
int i,j,p;
for(i=0;i<dim;i++)
{
for(j=0;j<dim;j++)
{
arr[i][j] = (dim*dim-1)-i*dim-j;
}
for(p=0;p<dim;p++)
{
printf("%d ", arr[i][p]);
if(i>=1)
printf("%d ", arr[i-1][p]);
}
}
printf("\n");
if(dim%2==0)
{
arr[dim-1][dim-3] = 1;
arr[dim-1][dim-2] = 2;
}
}
EDIT: it should compile now

Answer 1

You define your array with a[dim - 1][dim - 1], which is one short of the desired dimension. If the user enters "4", you create a 3×3 array.
Your array is two-dimensional and of variable length. Therefore, you must pass the dimension alongside the array in functions, at least for the last dimension. You do this correctly, but the code in ´initbehaves as if the array werea[dim][dim], when it's actuallya[dim - 1][dim - 1]`.
Define the array with the actual dimension, dim and access the elements with indices 0 through dim - 1. This is usually done in a loop like this:
for (int i = 0; i < dim; i++) ...
Seeing >= or dim - 1 something similar should make you wary.
Your program now looks like this:
#include <stdio.h>
void init(int dim, int arr[dim-1][dim-1]);
void print(int dim, int arr[dim-1][dim-1]);
int main(void)
{
int dim;
printf("Enter board dimension: ");
scanf("%d", &dim);
int arr[dim][dim];
init(dim, arr);
print(dim, arr);
return 0;
}
void print(int dim, int arr[dim][dim])
{
int i,j;
for(i = 0; i < dim; i++) {
for(j = 0; j < dim; j++) {
printf("%2d ", arr[i][j]);
}
printf("\n");
}
}
void init(int dim, int arr[dim][dim])
{
int i, j;
for(i = 0; i < dim; i++) {
for(j = 0; j < dim; j++) {
int ii = dim - 1 - i;
int jj = dim - 1 - j;
arr[i][j] = ii*dim + jj;
}
}
}