CODEWITHSUNDEEP
for-loopinfinite-loop
CodeNovice
CodeNovice

Reputation: 373

For loop won't end. Don't know why

I'm writing a for loop for a project that prompts the user to input a number and keeps prompting, continually adding the numbers up. When a string is introduced, the loop should stop. I've done it with a while loop, but the project states that we must do it with a for loop also. The problem is that the prompt keeps running even when 'a = false'. Could someone explain javascript's thinking process? I want to understand why it keeps running back through the loop even though the condition isn't met. Thank you

 var addSequence2 = function() {

        var total = 0;
        var a;

        for (; a = true; ) {
            var input = prompt("Your current score is " +total+ "\n" + "Next number...");

            if (!isNaN(input)) {
                a = true;
                total = +total + +input;
            }
            else if (isNaN(input)) {
                a = false;
                document.write("Your total is " + total);
            }
        }
 };

Upvotes: 1

Views: 1842

Answers (8)

Thomas Ayoub
Thomas Ayoub

Reputation: 29431

Here's your fixed code :

var addSequence2 = function() {

    var total = 0;
    var a = true;

    for(;Boolean(a);) {
        var input = prompt("Your current score is " +total+ "\n" + "Next number...");

        if (!isNaN(input)) {
            total = total + input;
        }
        else{
            a = false;
            document.write("Your total is " + total);
        }
    }
};

Upvotes: 0

KidneyChris
KidneyChris

Reputation: 857

There is a difference between a = true and a == true.

Your for-loop is basically asking "can I set 'a' to true?", to which the answer is yes, and the loop continues.

Change the condition to a == true (thus asking "Is the value of 'a' true?")

To elaborate, in most programming languages, we distinguish between assignment ("Make 'x' be 4") and testing for equality ("Is 'x' 4?"). By convention (at least in languages that derive their syntax from C), we use '=' to assign/set a value, and '==' to test.

If I'm understanding the specification correctly (no guarantee), what happens here is that the condition condenses as follows:

  1. Is (a = true) true?
  2. Complete the bracket: set a to true
  3. Is (a) true? (we just set it to true, so it must be!)

Upvotes: 3

JSK
JSK

Reputation: 583

for (; a = true; ), you are assigning the value to the variable "a" and it will always remain true and will end up in infinite loop. In JavaScript it should a===true.

Upvotes: 1

santa banta
santa banta

Reputation: 323

You should use a == true instead of a = true......= is an assignment operator

Upvotes: 1

Gerald
Gerald

Reputation: 677

for (; a = true; ) <-- this is an assignation

for (; a == true; ) <-- this should be better

Upvotes: 0

AllwinP
AllwinP

Reputation: 71

a == true. The double equal sign compares the two. Single equal assigns the value true to a so this always returns true.

Upvotes: 0

GodEater
GodEater

Reputation: 3717

I suspect you want your for to look like this :

for(;a==true;)

as a=true is an assignment, not a comparison.

Upvotes: 0

Resource
Resource

Reputation: 544

Try using the equal to operator, i.e. change

for (; a = true; ) {

to

for (; a == true; ) {

Upvotes: 2

Related Questions