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JavaScript JavaScript Loops, Arrays and Objects Simplify Repetitive Tasks with Loops `do ... while` Loops

Posted by Unsubscribed User
Unsubscribed User
4,479 Points

Why does this version of a 'do, while' number guessing game not work?

While revising the 'do, while' loop video and exercise, I tried this, but it doesn't work.

I think it generates a condition that will always evaluate 'true', but can someone clarify this more?

Is there anything wrong with generating a random number (1 - 10) and storing it in a variable in this way?

var randomNum = Math.floor(Math.random() * 10 + 1);

do {
  var guess = prompt("Guess a number between 1 and 10.");
  parseInt(guess);
} while ( guess !== randomNum )

document.write("you guessed the random number is " + randomNum);

4 Answers

Jon Mirow
Jon Mirow
9,864 Points

Hmm, that code seems to work for me. I added an alert so I'd know what number it had, and ran it a few times without error:

var randomNum = Math.floor(Math.random() * 10 + 1);

do {
  alert(randomNum)
  var guess = parseInt(prompt("Guess a number between 1 and 10."));
} while ( guess !== randomNum )

document.write("you guessed the random number is " + randomNum);
Jon Mirow
Jon Mirow
9,864 Points
Jon Mirow
Jon Mirow
9,864 Points

ho there!

parseInt returns the value, it doesn't change the variable in place, so the guess is always a string, so the condition is always false.

for example:

name = prompt("What's your name?") 
alert(name)
parseInt(name)
alert(name)
name = parseInt(name)
alert(name)

Only once the returned value is assigned to the variable does name change, so name becomes NaN because something like "Bob" isn't a number, so that's what parseInt() returns.

If you used this comparison:

while ( guess != randomNum )

You also wouldn't get the infinite loop, because == will attempt type conversion (though it's better to parseInt and use === usually)

Hope it helps :)

Unsubscribed User
Unsubscribed User
4,479 Points
Unsubscribed User
Unsubscribed User
4,479 Points

You're right - it does work.

When I first tested the code I kept entering the same number, thinking that 'var randonNum' was generating a new random number each time. But testing it again, I entered 1 then 2, and up to 10 if necessary, before I got the single random number value stored in 'randomNum'.

Thanks for looking at this Jon.

Jon Mirow
Jon Mirow
9,864 Points

No worries!

Mistakes are a good thing - just yesterday I spent 20 minutes trying to work out why a test I'd put in my code wasn't working, then remembered I'd commented out it's output lol.

It's the code that works first time you've really gotta be scared of lol

Unsubscribed User
Unsubscribed User
4,479 Points
Unsubscribed User
Unsubscribed User
4,479 Points

This was an earlier attempt that I think addresses the parsing and storing of the number value in 'guess', but it is still not working ? 

var randomNum = Math.floor(Math.random() * 10 + 1);

do {
  var guess = parseInt(prompt("Guess a number between 1 and 10."));
} while ( guess !== randomNum )

document.write("you guessed the random number is " + randomNum);