从键盘输入一个四位正整数。首先分离出该正整数的每一位数字，并按逆序输出各位数字

#include<iostream>
using namespace std;
void main()
{
int num;
cout<<"input the data:"<<endl;
cin>>num;
if(num<1000||num>9999)
do{
cout<<"input wrong,try again!"<<endl;
cin>>num;
}while(num<1000||num>9999);
int temp=num,a[4],i=0;
cout<<"the reverse sorted is:"<<endl;
for(i=0;i<4;i++)
{
a[i]=temp%10;
temp/=10;
cout<<a[i];
}
cout<<endl;
for(i=0;i<4;i++)
for(int j=i+1;j<4;j++)
{
if(a[i]>a[j])
temp=a[i];
a[i]=a[j];
a[j]=temp;
}
cout<<"the maximum number which build by the "<<num<<" is:"<<endl;
for(i=0;i<4;i++)
cout<<a[3-i];
cout<<endl;
cout<<"the minimum number which build