Check variable for value

[W A]

I have declared a double without a value. Later on I give it the value of the solution of an equation. The equation might however not have a solution all the time, which would result in an empty variable. I need a way to check if the variable is empty or not so that my program knows if it should carry on or do something else. Any suggestions?

[Athar]

Variables always have a value, they cannot be empty.
For custom classes you can define a state in which they can be considered "empty" (such as a container having no elements), but types like double always have a value, even if you don't initialize them. In that case, their value in undefined.
Instead, you should have a bool variable that indicates whether there was a solution or not.

[W A]

How would that work then?

bool check=false;
if("equation")
     check=true;

Or am I completely wrong?

[Athar]

Yeah, something like that works.

[coder777]

You can use boost::optional for that purpose: http://www.boost.org/doc/libs/1_46_1/libs/optional/doc/html/index.html