Checking if a value is within a range in if statment

Question

I did below:

if( \'0\' <= infix.at(i)<= \'9\'){
// some logic
}

Compiler gave me warning unsafe use of type \'bool\' in operation. I

Answer 1

The first version would be evaluated like this:

if( ( '0' <= infix.at(i) ) <= '9' )

which is why you get a warning about bool - you wind up with true/false <= '9' which doesn't make sense.

Some languages allow you to chain comparison operators, but C++ is not one of them.