How can I compare two strings without using strcmp() function?

Not sure if it's exactly the same, but since PHP is based off C++, this might help.

In PHP, you can compare string with the == and === operators. == means same value, and === means same value and type.

Is this a trick question?

Do a strlen on each string make sure they are the same len and then do a memcmp

Or write your own strcmp function!

What is the purpose of this question - homework or an interview?

Frist of all, strcmp is a C function, not c++.
You can find the answer with example in compare [C++ Reference]