Why int _$[:>=

Today I found something like

 int _$[:>=<%-!.0,};

in some old code, but in fact the code is not comment out but seems no report compile error for this line, I test it separately and it can compile too:

int main(){
    int _$[:>=<%-!.0,};
    return 0;
}

why can it compile?

via Chebli Mohamed