If you program in C, you've probably used what is called the ternary operator a million times in expressions like this:

    value = user_value ? user_value : default_value;

Where you test user_value and, if it's non-zero, you store it in value; otherwise, you set value to default_value.

What you may not know is that, thanks to a gcc (and others) extension, you can abridge that expression to this:

    value = user_value ?: default_value;

This ?: thing is colloquially named the 'Elvis' operator (if you don't see why, just look at it with you head slightly slanted to the left).

https://en.wikipedia.org/wiki/Elvis_operator