直接当成数字来比较都可行

#include<iostream>
using namespace std;
int main()
{
    string a,b,c;
    cin>>a>>b>>c;
    if(a<b){
        if(a>c) cout<<c<<endl<<a<<endl<<b;
        else{
            if(b>c) cout<<a<<endl<<c<<endl<<b;
            else cout<<a<<endl<<b<<endl<<c<<endl;
        }
    }
    else{//a>b
        if(b>c) cout<<c<<endl<<b<<endl<<a;
        else{ //b<c
            if(a>c) cout<<b<<endl<<c<<endl<<a;
            else cout<<b<<endl<<a<<endl<<c;
        }
    }
    return 0;
}