What is a flag variable?

Question

Recently I came across flag variables, but I have no idea what they do.

I am little unsure about when to use a flag variable and how to go about it.

I Google

Answer 1

A flag is a variable used to have some value until some condition becomes true,then we change it to false and print the output (Initially flag considered as true)

Answer 2

No matter what language you are using, the concept of flag variables is always the same: a variable that stores a boolean value. A boolean value is one which is always either true or false or is either 0 or 1 (depending on the language and programmer's personal preference).

Flag variables (also called boolean variables, or often just flags) are used to indicate a condition which can only be either of the two boolean values. The value of the variable can toggle depending on events in the program.

A JavaScript example:

var isRaining = false; // It is either raining or not raining.

var statusCode = true; // Status codes may be boolean values.

Answer 3

Flag Variables Defined and Uses says:

A flag variable, in its simplest form, is a variable you define to have one value until some condition is true, in which case you change the variable's value. It is a variable you can use to control the flow of a function or statement, allowing you to check for certain conditions while your function progresses.

As an example:

// errors is the flag variable
var errors = 0;

for(var i = 0; i < 10; i++) {
  if(i == 6) {  // Your error condition
    errors++;
  }
}

if(errors) {  // Is the flag "up"? (i.e. > 0)
  alert("There was a problem!");
}

Answer 4

Flag variables are the same for all languages, whether it's RUBY, Python, Javascript or C++.

A flag variable is usually given one value, 0 or 1, True or False. It's used as a Boolean variable where the result toggles between 0 (False) and 1 (True) or as used by the programmer. Some prefer flag = 0 and change it to flag = 1 in the program to perform an action.