Compilation error while adding two shorts

[David Zaragoza via Digitalmars-d-learn]

Hello

I'm trying to compile the following program:
module main;

int main(string[] argv){
        short asd = 1;
        short qwe = asd + asd;
        return 0;
}

And the compiler gives this error:

C:\David>dmd simple
simple.d(5): Error: cannot implicitly convert expression 
(cast(int)asd + cast(in
t)asd) of type int to short

Why is there a cast if I'm adding to shorts?

Regards