למה זה מודיע לי שגיאה ?

קוד:

 // nice libary

// http://www.cplusplus.com/forum/articles/6046/
// http://www.cplusplus.com/reference/clibrary/cstring/
string data = NULL;
cout << "enter string plz: ";
getline(cin, data);
do{
string newdata = NULL;
cout << "enter another string plz: ";
getline(cin, newdata);
if (strlen(newdata) > strlen(data))
data = newdata;
else if (strlen(newdata) == 0)
break;
} while(true);
cout << "longest string is: " << data << endl;

C:\Users\Admin\Desktop\Homework\HomeWork.cpp(205) : error C2664: 'strlen' : cannot convert parameter 1 from 'class std::basic_string<char,struct std::char_traits<char>,class std::allocator<char> >' to 'const char *'
No user-defined-conversion operator available that can perform this conversion, or the operator cannot be called
C:\Users\Admin\Desktop\Homework\HomeWork.cpp(205) : error C2664: 'strlen' : cannot convert parameter 1 from 'class std::basic_string<char,struct std::char_traits<char>,class std::allocator<char> >' to 'const char *'
No user-defined-conversion operator available that can perform this conversion, or the operator cannot be called
C:\Users\Admin\Desktop\Homework\HomeWork.cpp(207) : error C2664: 'strlen' : cannot convert parameter 1 from 'class std::basic_string<char,struct std::char_traits<char>,class std::allocator<char> >' to 'const char *'
No user-defined-conversion operator available that can perform this conversion, or the operator cannot be called
Error executing cl.exe.

קוד מתוקן

קוד:

 // http://www.tek-tips.com/faqs.cfm?fid=5193
// http://www.cplusplus.com/forum/articles/6046/
// http://www.cplusplus.com/reference/...stream/getline/
// http://www.cplusplus.com/reference/clibrary/cstring/
// The getline template function reads an extra character after encountering the delimiter
// http://support.microsoft.com/defaul...B;EN-US;q240015
// C:\Program Files\Microsoft Visual Studio\VC98\Include\STRING
string
data,
newdata;
cout << "enter string: ";
getline(cin, data);
cout << "enter another string plz: ";
while(getline(cin, newdata))
{
if (newdata.empty() || newdata.length() == 0)
break;
if (newdata.length() > data.length())
data = newdata;
cout << "enter another string plz: ";
}
cout << "longest string is: " << data << endl;