大家帮忙看下这个小程序的原理是什么

#include <iostream>
using namespace std;
bool isPN(int num)
{
        int o = num;
        int tmp = 0;
        while(num != 0) {
                tmp *= 10;
                tmp += num % 10;
                num /= 10;
        }
        if (tmp == o) {
                return true;
        }
        return false;
}
int main()
{
        int number;
        cout<<"输入一个整数：";
        cin>>number;
        if(isPN(number))
                cout<<"是回文数"<<endl;
        else
                cout<<"不是回文数"<<endl;
        return 0;
}