C++蛇形填数

//#include <fstream> 
#include<iostream>
#include<iomanip>
using namespace std;
void test(int aa[20][20],int m,int n,int Dire,int num);//声明
   void main() 
   { 
 //  ifstream InFile("in.txt"); 
   int n=0,i=0,j=0,num=1;
   int aa[20][20]={0};
//   InFile>>n;
   cin>>n;
   for(i=0;i<n;i++)
   {
   aa[i][n-1]=num;
   num++;
   }
   for(i=n-1;i>0;i--)
   {
   aa[n-1][i-1]=num;
   num++;
   }
   for(i=n-1;i>0;i--)
   {
   aa[i-1][0]=num;
   num++;
   }
   for(i=1;i<n-1;i++)
   {
   aa[0][i]=num;