What is a flag variable?

Solution 1:

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!");
}

Solution 2:

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)

Solution 3:

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.