Do while loop with a cout statement

Question

So I have a general question about the do/while loop. I'm learning C++ and I know that you can write something like that:

do{
....
} while(a<10 && cout<<"message");

The point is, that i know this is possible in c++, but do we really do that? I mean, the "cout" thing inside the while?

Answer 1

Your while loop is equivalent to

do {
    ...
    cout << "message";
while(a < 10 && cout);

because cout << ... returns cout again. Then, the question is, what does it mean to write statements like

while( cout );

or

if (cout) ...

The cout object has a conversion to boolean which is used here. It's implementation is checking !fail(), so

if (cout) ...

is equivalent to

if (!cout.fail()) ...

and

do { ... }
while(cout);

is equivalent to

do { ... }
while(!cout.fail());

Finally, fail returns true if the stream failed to produce output.