While Loops and Flags

When writing programs that don't necessarily deal with numbers, you may use a flag based loop to help you do repetitions.

There are some problems that the end point of the task is unclear. In such scenario, it is helpful to write a potential infinite loop and construct an exit mechanism to get out of it.

Example of a flag

Please note that it does not need to be called a flag, but it is a representation of a flag being either being true or false.

let flag = true;

while (flag) {
    console.log("Hello!");
    
    let end = prompt("Do you want to end the loop? (Yes/No): ");
    
    if (end == "Yes") {
        flag = false;
        console.log("good bye!");
    }
}

1. Initialization: You start by setting a variable called flag to true.

2. Condition Check: You have a loop that will continue to run as long as flag is true.

3. Loop Execution: Inside the loop, three main actions occur:

   • The message “Hello!” is printed to the console.

   • The program prompts the user with the question “Do you want to end the loop? (Yes/No):” and waits for the user’s input.

   • If the user types “Yes”, the flag variable is set to false, and the message “good bye!” is printed to the console.

4. Repetition: After each iteration, the loop checks the condition again. If flag is still true, the loop repeats the actions. This process continues until the user types “Yes” (case sensitive).

5. Termination: When the user types “Yes”, the condition flag becomes false, so the loop stops running, and the program prints “good bye!”.