What is a boolean flag

Question

I'm taking a course in Visual Basic 2010 and I'm trying to get a grasp on this new term called a flag. I kind of understand that it has something to do with a boolean condition. I don't quite understand what a flag is. I see references to it using the term flag. I understand it has something to do when a boolean, a condition triggers a flag. But what is the flag. How do you identify it? Can somebody give me an example.

Answer 1

In general, "Flag" is just another term for a true/false condition.

It may have more specific meanings in more specific contexts. For instance, a CPU may keep "arithmetic flags", each one indicating a true/false condition resulting from the previous arithmetic operation. For instance, if the previous operation was an "ADD", then the flags would indicate whether the result of the add was zero, less than zero, or greater than zero.

I believe the term comes from flags used to signal a go/no go condition, like, a railroad flagman indicating whether or not it is safe for the train to proceed.