Print perfect square spiral number pattern

1    2    3    4    5    620   21   22   23   24   719   32   33   34   25   818   31   36   35   26   917   30   29   28   27   1016   15   14   13   12   11 

C Programming Language Loop control in C Language (Article) Loop control in C Language (Program)

1755

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1    2    3    4    5    6    7    8    9    10
36   37   38   39   40   41   42   43   44   11
35   64   65   66   67   68   69   70   45   12
34   63   84   85   86   87   88   71   46   13
33   62   83   96   97   98   89   72   47   14
32   61   82   95   100  99   90   73   48   15
31   60   81   94   93   92   91   74   49   16
30   59   80   79   78   77   76   75   50   17
29   58   57   56   55   54   53   52   51   18
28   27   26   25   24   23   22   21   20   19

Program:

/**
 * C program to print perfect square number pattern
 */

#include <stdio.h>

#define SIZE 6 // Size is always even

int main()
{
    int i, j, N;
    int board[SIZE][SIZE];
    int left, top;

    left = 0;
    top  = SIZE - 1;
    N    = 1;

    for(i=1; i<=SIZE/2; i++, left++, top--)
    {
        // Fill from left to right
        for(j=left; j<=top; j++, N++)
        {
            board[left][j] = N;
        }

        // Fill from top to down
        for(j=left+1; j<=top; j++, N++)
        {
            board[j][top] = N;
        }

        // Fill from right to left
        for(j=top-1; j>=left; j--, N++)
        {
            board[top][j] = N;
        }

        // Fill from down to top
        for(j=top-1; j>=left+1; j--, N++)
        {
            board[j][left] = N;
        }
    }

    // Print the pattern
    for(i=0; i<SIZE; i++)
    {
        for(j=0; j<SIZE; j++)
        {
            printf("%-5d", board[i][j]);
        }
        printf("\n");
    }

    return 0;
}

Output:

1    2    3    4    5    6    7    8    9    10
36   37   38   39   40   41   42   43   44   11
35   64   65   66   67   68   69   70   45   12
34   63   84   85   86   87   88   71   46   13
33   62   83   96   97   98   89   72   47   14
32   61   82   95   100  99   90   73   48   15
31   60   81   94   93   92   91   74   49   16
30   59   80   79   78   77   76   75   50   17
29   58   57   56   55   54   53   52   51   18
28   27   26   25   24   23   22   21   20   19

Explanation:

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