//在屏幕上打印杨辉三角。
/*
1

1 1

1 2 1

1 3 3 1

……*/

#define _CRT_SECURE_NO_WARNINGS 1
#include<stdio.h>

#define N 14
void main()
{
    int i, j, k, n = 0, a[N][N];  
    while (n <= 0 || n >= 13)
    {  
        printf("请输入要打印的行数：");
        scanf("%d", &n);
    }
    printf("%d行杨辉三角如下：\n", n);
    for (i = 1; i <= n; i++)
        a[i][1] = a[i][i] = 1; 
    for (i = 3; i <= n; i++)
        for (j = 2; j <= i - 1; j++)
            a[i][j] = a[i - 1][j - 1] + a[i - 1][j];  
    for (i = 1; i <= n; i++)
    {
        for (k = 1; k <= n - i; k++)
            printf("   ");  
        for (j = 1; j <= i; j++)  
            printf("%6d", a[i][j]);

        printf("\n");  
    }
    printf("\n");
    return 0;
}