C蛇形填数不知道为啥没有结果

代码找不出问题但是出不了结果

#include<stdio.h>
#include<math.h>
#include<time.h>
#include<string.h>
#define max 100
int a[max][max];
int main()
{
    int x, y;
    int n;
    int start;
    scanf("%d",&n);
    memset(a, 0, sizeof(a));
    x = 0;
    y = n - 1;
    start = a[x][y] = 1;
    while (start = n * n)
    {
        while (x + 1 < n && !a[x + 1][y])a[++x][y] = ++start;
        while (y - 1 >=0 && !a[x][y-1])a[x][--y] = ++start;
        while (x-1>= 0 && !a[x - 1][y])a[--x][y] = ++start;
        while (y + 1 < n && !a[x + 1][y])a[++x][y] = ++start;

    }
    for (x = 0; x < n; x++)
    {
        for (y = 0; y < n; y++)
            printf("%3d", a[x][y]);
        printf("\n");

    }
    return 0;
}

17行循环结束条件不对

修改处见注释，供参考：

#include<stdio.h>
#include<math.h>
#include<time.h>
#include<string.h>
#define max 100
int a[max][max];
int main()
{
    int x, y;
    int n;
    int start;
    scanf("%d",&n);
    memset(a, 0, sizeof(a));
    x = 0;
    y = n - 1;
    start = a[x][y] = 1;
    while (start < n * n)//while (start = n * n) 修改
    {
        while (x + 1 < n && !a[x + 1][y]) a[++x][y] = ++start;
        while (y - 1 >=0 && !a[x][y-1])   a[x][--y] = ++start;
        while (x-1>= 0 && !a[x - 1][y])   a[--x][y] = ++start;
        while (y + 1 < n && !a[x][y+1])   a[x][++y] = ++start;//修改
        //while (y + 1 < n && !a[x + 1][y]) a[++x][y] = ++start;

    }
    for (x = 0; x < n; x++)
    {
        for (y = 0; y < n; y++)
            printf("%3d", a[x][y]);
        printf("\n");

    }
    return 0;
}