C语言题目不会，求大神给思路

Question

Answer 1

 #include<iostream>
#include<cstring>
#include<algorithm> 
#include<cstdlib>
#include<Windows.h>
using namespace std;
int main()
{
    int n;
    while(cin>>n){
    if(n==0)break;
    DWORD start_time=GetTickCount();
    char str[15];
    memset(str,0,sizeof(0));
    for(int i=1;i<=n;i++){
        str[i]=i+48;
    }
    for(int j=1;j<=n;j++){
            cout<<str[j];
        }
    cout<<endl;
    while(next_permutation(str+1,str+n+1)){
        for(int j=1;j<=n;j++){
            cout<<str[j];
        }
        cout<<endl;
    }
    DWORD end_time=GetTickCount();
    cout<<"The run time is:"<<end_time-start_time<<"ms!"<<endl;
    }
    return 0;
 }