Error: expected '=', ',', ';', 'asm' or '__attribute__' before 'int'

I spent much time on figuring this problem out. I don't actually know where is the problem. All things look fine.

Finally, my workmate told me that somehow if you changed .c to .cpp, some problems were gone. I tried it and it works like a charm!

So, in Ubuntu Qt development environment, if a problem you can't figure it out, try to change the extension name of the source code!