字符串变量的运算

例：输入3个字符串，要求字母由大到小顺序输出

#include<iostream>
#include<string>
using namespace std;

int main(void)
{
    string string1, string2, string3, temp;

    cout << "please input three strings:";
    cin >> string1 >> string2 >> string3;

    if(string2 > string3)
    {
        temp = string2;
        string2 = string3;
        string3 = temp;
    }
    if(string1 <= string2)
    {
        cout << string1 << " " << string2 << " " << string3 << endl;
    }
    else if(string1 <= string3)
    {
        cout << string2 << " " << string1 << " " << string3 << endl;
    }
    else
    {
        cout << string2 << " " << string3 << " " << string1 << endl;
    }
    return 0;
}