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Comment by gpderetta | Hacker News Reader

FWIW, !! is a fairly idiomatic way to cast a value to bool.

Ints are automatically converted to bool, there is no need to cast. What this does is it restricts the int to 1 or 0. The clean way to write this is x ? 1 : 0. This is understandable even if you don't know the Boolean inversion of 0 is 1 (Which isn't self-evident. For example in Basic its -1).

They are converted to bool in bool context. Outside of that you have to force it.

   int countNonZero = 0;
   for (int i = 0; i < values.size(); ++i) {
       countNonZero += !!values[i];
   }

Also c++ has explicit operator bool();

edit: not a great example as values[1] >0 would be better.

You don't have to enforce a conversion from int to bool if you just want a bool. In this example you don't want to increment by 'bool', you want to increment by 1 or 0 (which are ints). So you use !!x to convert to bool and back to int.

The reason I'm pointing this out is that often enough I had to work with code where this distinction was unknown to the author and you come across code like if (!!x) which is, again, just nonsense.

edit: not a great example as values[1] >0 would be better.

Only if that's an array of unsigned ints, as otherwise the code would count only positive nonzeros.

You can also typecast to bool since C99. (bool)x if you include <stdbool.h> or (_Bool) if not.

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