Defining a variable in the condition part of an if-statement?

Question

I was just shocked, that this is allowed:

if( int* x = new int( 20 ) )
{
    std::cout << *x << \"!\\n\";
    // delete x;
}
else
{
    std::cout         


        

Answer 1

Not really an answer (but comments are not well suited to code samples), more a reason why it's incredibly handy:

if (int* x = f()) {
    std::cout << *x << "\n";
}

Whenever an API returns an "option" type (which also happens to have a boolean conversion available), this type of construct can be leveraged so that the variable is only accessible within a context where it is sensible to use its value. It's a really powerful idiom.