Looking for a center in a square array

Question

My problem is about a square array. I have a dynamic array in order to fill with numbers from 1 to N starting at 'the center' and spiralling out. If I have an array 6x6, I need to fill it in the way shown in the picture. If I have an array with an even number of cells in each direction, I need pick out a square in my array, and begin to count with the first element in a square. But if I have an array with an odd number of cells, I need to pick out a center of the array.

My main problem is to think of an algorithm which can help me to reach my "center". This is my code which I use for creating and printing my array:

#include <stdlib.h>
#include <stdio.h>
#include <malloc.h>

int** create_array(int, int);
void fill(int **, int, int);
void print_my_array(int**, int, int);
void print_my_array(int** ,  int  , int );
int main() {

    int **a, x, y;
    printf("Enter x: ");
    scanf("%d", &x);
    printf("Enter y: ");
    scanf("%d", &y);

    a = create_array(x, y);
    fill(a, x, y);
    print_my_array(a, x, y);
    return 0;
}

int** create_array(int rows, int cols) {
    int **arr=NULL,i;
    if (!(arr = (int**)malloc(rows*sizeof(int*)))) {
        printf("Error");
        exit(0);
    }
    for ( i = 0; i <rows; i++){
        if (!(arr[i] = (int*)malloc(cols*sizeof(int)))) {
            printf("Error");
            exit(0);
        }
        return arr;
}
return arr;
}

    void fill(int **arr, int x, int y) {
            //HELP
    }

void print_my_array (int** array,  int x, int y)
{
    int i, j;
    for(i=0;i<x;i++)
    {
        for(j=0;j<y;j++)
        {
            printf("%d ", array[i][j]);
        }
        printf("\n");
    }
    printf("\n");
}

Answer 1

The center of the nxn array is (floor((n-1)/2),floor((n-1)/2)) [0 indexing]. But we will solve it differently. If n is even then it will end in

x x x 16
x 1 x x
x x x x
x x x x

x x x x x 36
x x x x x x
x x 1 x x x
x x x x x x
x x x x x x
x x x x x x

So for even n it always ends in [0,n-1]. Now what you will do to fill it up?

You know the numbers will be n*n, n*n-1,n*n-2...2,1.

Similarly for n odd

x x x
x 1 x
9 x x

 x x x x x
 x x x x x
 x x 1 x x
 x x x x x
25 x x x x

Hope you get what we want to do from these pics?

Code

int nc=n*n;
int ans[n][n];
fill ans[][] with -1
int row=n-1,col=0;
if(n&1)
{
while(nc>0)
{
   for(int i=row;i>=0 && ans[i][col]==-1;i--)
   {  
      row--;ans[i][col]=nc; nc--;
   } 
   row++;col++;
   for(int j=col;j<=n-1 && ans[row][j]==-1;j++)
   {
      col++;ans[row][j]=nc; nc--;
   }
   col--;row++;
   for(int i=row;i<=n-1 && ans[i][col]==-1;i++)
   {
      row++;ans[i][col]=nc;nc--;
   }
   row--;col--;
   for(int j=col;j>=0 && ans[row][j]==-1;j--)
   {
     col--;ans[row][j]=nc;nc--;
   }
   col++;row--;
}

}
else

{
    row=0;col=n-1;
    while(nc>0)
    {

       for(int i=row;i<=n-1 && ans[i][col]==-1;i++)
       {
          row++;ans[i][col]=nc;nc--;
       }
       row--;col--;
       for(int j=col;j>=0 && ans[row][j]==-1;j--)
       {
         col--;ans[row][j]=nc;nc--;
       }
       col++;row--;
       for(int i=row;i>=0 && ans[i][col]==-1;i--)
       {  
          row--;ans[i][col]=nc; nc--;
       } 
       row++;col++;db(row);db(col);

       for(int j=col;j<=n-1 && ans[row][j]==-1;j++)
       {
          col++;ans[row][j]=nc; nc--;
       }
       col--;row++;
    }
}
//print ans[n][n]