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#include <stdio.h>
#include <string.h> // memset()

#define EMPTY                    0

#define ROW(pos, size)           ( (pos) / size )
#define COL(pos, size)           ( (pos) % size )
#define ROW_LENGTH(size)         ( ((size) - 1) * (size) )

#define POSUPNRIGHT(pos, size)   ( POSRT(POSUP((pos), (size)), (size)) )
#define POSRT(pos, size)   ( COL((pos), (size)) == (size) - 1 ? (pos) - ((size) - 1): (pos) + 1 )
#define POSUP(pos, size)   ( ROW((pos), (size)) == 0 ? (pos) + ROW_LENGTH((size)) : (pos) - (size) )
#define POSDN(pos, size)   ( ROW((pos), (size)) == (size) -1 ? (pos) - ROW_LENGTH((size)) : (pos) + (size) )

int main(void)
{
    int pos, size;
    printf("Enter size of magic square (odd 1-99): ");
    scanf("%d", &size);
    
    int square[size * size];
    memset(square, EMPTY, sizeof(square));        // init table to EMPTY

    pos = size / 2;
    square[pos] = 1;
    
    for (int i = 2; i < (size * size) + 1; i++) {
        int upnright = POSUPNRIGHT(pos, size);
        pos = square[upnright] == EMPTY ? upnright : POSDN(pos, size);
        square[pos] = i;
    }
        
    // print magic square
    for (int i = 0; i < size * size; i++) {
        if (i != 0 && i % size == 0)
            putchar('\n');
        printf("%4d", square[i]);
    }
    putchar('\n');
        
    return 0;
}