zoj 1831 Substitution Cypher

#include <iostream>#include <string.h>#include <cstdio>#include <map>using namespace std;map <char,char>mymap;int main(){    int i;    string a,b,s;    getline( cin,a );    getline( cin,b );    for( i=0;i<a.size();i++ )    {        mymap[ a[i] ]=b[i];    }    cout<<b<<endl;    cout<<a<<endl;    while(  getline( cin,s ) )    {        if( s=="" ) break;        for( i=0;i<s.size();i++ )        { if( mymap.find(s[i])==mymap.end() )     cout<<s[i]; else cout<<mymap[ s[i] ];        }        cout<<endl;    }    return 0;}