Let’s assume that you want to set all non-zero values to 1.
Usually, I’d prefer the simple and understandable way:

if(a != 0)
   a = 1;

or

a = (a==0) ? a : 1;

I found out a cool trick that I didn’t want to keep back from you:

a = !!a;

Funny, but too adventurous to use it in real life