삼각형 출력

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

int main()
{
    int a[10][10] = { 0 }, m, left, right, k, i, j;

    printf("INPUT DATA = ");
    scanf("%d", &m);

    left = 0, right = m - 1, k = 1;

    for (i = 0; i < m; i++)
    {
        for (j = right; j >= left; j--)
        {
            a[i][j] = k++;
        }

        if (i < m / 2)
        {
            left++; right--;
        }

        else
        {
            left--; right++;
        }
    }

    for (i = 0; i < m; i++)
    {
        for (j = 0; j < m; j++)
        {
            if (a[i][j] > 0)
            {
                printf("%3d", a[i][j]);
            }
            else printf("   ");
        }
        printf("\n");
    }

    return 0;
}