You can compile your solution by pressing the 'Compile' button in the arena.
Any compile errors will be displayed below the code editor.

To make sure that your solution is compiling on our system, make sure that you first compile, then test your solution.
If you use the test button without compiling, your solution will still be compiled, but detailed compile error message will not be displayed, instead you will get 'Compile errors' as result of the testing.