Jump to content
  • Announcements

    • boen_robot

      Guidelines and Netiquette   03/28/2017

      Posting Problems:   Having problems posting your topic? Read through this: To join, you agree to our terms and conditions and fill out and submit a registration form. An activation email will be sent to your email adress, so you'll need to verify your account. After that the account has to be validated by one of the moderators. This will mean that it can take up to a day to be activated. A couple of things to remember to ensure approval: Don't use an email address in one of those $2 four character .com domains eg. xyds.com. These will be deleted and the domain added to the banned list. Don't use an email address that is within a domain with a bad reputation for spam. A Google search is run on every email address and email domain. Don't sign up with an email address that doesn't exist, doesn't work or requires the sender to answer a quiz before their email can get to you. Put your country and or state and city in the signup form. Blank forms will go to the botton of the "to do" list. And make sure that your email address and your country match, saying you're from Alabama and using a .ru email address is not going to get you activated. After a membership is activated the first few posts will be monitored. Posting spam or unapproved topics described in the agreement results in an immediate ban. The email provider and the IP addresses associated with the account will be banned and all posts will be deleted. These strict measures have been deemed necessary to hinder spam. Sorry for any inconvenience this causes, but it's not liable to change. If, after reading this, you still can't post and don't understand why, contact one of the Moderators listed here.   Topic Guidelines   Including the following information can expedite an accurate response from board members: Must be a Specific Problem or Question related to web design and development Include Code in Question (wrap with   for small blocks of code and for longer blocks   ) Include Code Author Include Extra Notes/Modifications/Attempts Include web link to page/file when possible Content Guidelines   You may not post, upload, link to, or email any Content that contains, promotes, gives instruction about, or provides prohibited Content. Prohibited Content includes any Content that breaks any local, state, county, national or international law. Prohibited Content also includes: No direct or indirect advertising or websites, forums, products, services No hijacking of posts (do not post your question in someone elses) Content that infringes upon any rights [ex. MP3s and ROMs] (including, but not limited to, copyrights and trademarks) Abusive, threatening, defamatory, racist, or obscene Viruses or any other harmful computer software False Information or libel Spam, chain letters, or Pyramid schemes Gambling or Illicit drugs Terrorism Hacking or cheating for internet/online games Warez, Roms, CD-Keys, Cracks, Passwords, or Serial Numbers Pornography, nudity, or sexual material of any kind Excessive profanity Invasive of privacy or impersonation of any person/entity Hacking materials or information Posting Tips   There are more BBcodes than there are buttons for on the reply menu. To get the full list, click "BB Code Help" underneath the clickable smilie face menu. Use   for small snippets of code Use   for lengthy snippets of code Use   if your snippet is HTML (optional) Use   if your snippet is SQL (optional) Rules of Conduct   Be nice. There's no need for calling someone stupid if they ask an 'easy' question. Keep your avatars and signatures absolutely child friendly. We have a younger audience on this forum. Keep your language appropriate for the same reason above. Do not PM moderators for help on the forum. Post on the topic, or create a new one.   Spam:   Recently, as you have all without doubt noticed, we have had lots of spam and advertisement on the forum. Therefore, we'd like to alert you as to what to do when you have found any of the aforementioned annoying messages: it. Immediately. Give a clear reason, please, if the advertising is not evident. DO NOT POST! Report, let the post stay as is, and we will get to it, meanwhile if you continue to post as normal in the other threads, it won't be on the top so long. Refrain from PMing the member. This won't help at all, as they are most likely spambots anyway. Thank you.       Images in signatures:   After thinking of users on dial-up, we have decided to enforce the following rules regarding signatures. Please pay heed to them. Respecting these rules is respecting the members on this forum with dial-up. Signature rules: No animated images AT ALL. No matter the amount of animation. Maximum image widthxheight: 300x150 Maximum image (file) size: 15kb Use calm colors. Do not use highly contrasting images in your signature, as this can get really annoying when seeing several posts from one member in the same thread. The same prohibited content goes for images as for posts. Lastly, use common sense. No lengthy signatures please. Save us some scrolling. Thank you.       Links in signatures:   Please understand that w3schools.com only exists because of voluntary work and is barely supported by the advertising littered throughout the tutorials and the forum. So, please, stop advertising other sites. DO not post links that drive traffic away from the w3schools domain - especially to a site that offers similar if not identical information. Please help support the site by keeping individuals on it. Thank you. Here are some guidelines as to what you can put in your signature: w3schools links --> allowed w3.org links --> allowed browser links --> allowed html editor links --> allowed personal sites --> allowed tutorial sites competing with w3schools --> NOT allowed sites completely irrelevant to webprogramming and this forum --> NOT allowed   Thanks for understanding, and for taking the time to read this. ~W3Schools Modstaff~
Sign in to follow this  
Grabeorama

Adding One To A Variable

Recommended Posts

Here is my code:in the <head>

<script>var number;function myfunction()	{		number+=1;	}</script>[code]in the <body>[code]<input type="button" value="Add 1 to aidan" onclick="myfunction()">	<script>		document.write(number);	</script>

What I want, is that when I click the button, it adds one to the variable "number" is there something wrong with this code?

Share this post


Link to post
Share on other sites

In some languages, if you add 1 to an undefined variable, it casts the variable into a number, with the value 0, and does the add. Javascript is so loosely typed you'd think it would allow that, but it doesn't. Change your first line to this:var number = 0;Hint:Start writing things like number++ instead of number += 1. It's not better--just more idiomatic. You'll look more like one of the gang. :)

Share this post


Link to post
Share on other sites
It's not better--just more idiomatic.
Well, theoretically, it should be slightly faster as the interpreter doesn't have to interpret the "1". Benchmark anyone?

Share this post


Link to post
Share on other sites

It still doesn't change the variable "number"The part where I have document.write(number); still shows "0" after I have pushed the button.This is the code I'm using now:

<head><title>New Page 1</title>	<script>	var number = 0;	function myfunction()		{			number++;		}	</script></head><body>	<input type="button" value="Add 1 to number" onclick="myfunction()">	<script>	document.write(number);	</script></body>

Share this post


Link to post
Share on other sites

That's because your second script executes as the page loads. It is not associated in any way with your button, and it never runs again, no matter how many times you push the button. (If it did, you'd be in trouble, because it would erase your page!) myfunction() is associated with your button because you explicitly told it to be, in your onclick attribute.If you want to check the value of number, add a line like this to myfunction():alert(number);And please, please, please stop using document.write().

Share this post


Link to post
Share on other sites

o.k.Is there anyway of checking it without an alert box?I want to make a sort of slideshow for pictures, so when you click the left arrow it takes 1 from number and when you click the right arrow it adds one to number. Then depending on the value of number I would display the appropriate image.and what could I use instead of document.write() ?Thanks :)

Share this post


Link to post
Share on other sites

Create a page element and write to its innerHTML property.

<div>   <p id="message">   </p></div>

el = document.getElementById("message");el.innerHTML = "Any string you like";

Share this post


Link to post
Share on other sites
I don't quite get what you mean, where do I put this code?
The second part - ideally, at the end of your myfunction() function, replacing "Any string you like" with the actual string of course.The first part - anywhere within the body of your HTML document.

Share this post


Link to post
Share on other sites

Thanks :)It still doesn't work though :)All it shows is the button and underneath it has the number "0" that doesn't change when the button is clicked.Now I have this code:

<html><head><title>New Page 1</title>	<script type="text/javascript">		var number = 0;		function myfunction()			{				number++;				el = document.getElementById("message");				el.InnerHTML = "Hello There";			}	</script></head><body>	<input type="button" value="click me!" onclick="myfunction()">	<div>		<p id="message"></p>		<script>			document.write(number);		</script>	</div></body></html>

Thanks to those who have helped! :)

Share this post


Link to post
Share on other sites
		function myfunction()			{				number++;				el = document.getElementById("message");				el.innerHTML = number; // LOWERCASE i			}

Share this post


Link to post
Share on other sites

Sorry about the double post but I was wondering, is there a more efficient way of doing this:

<html><head>	<title>Black - Home</title>	<link type="text/css" rel="stylesheet" href="black_css.css">	<script type="text/javascript">		var image = 0;		var number = 0;		function picture_add()			{				if (image<4)					{		   			image++;		   		}		   	switch (image)		   		{		   			case 0:		   				number="This is zero";		   				break;		   			case 1:		   				number="This is one";		   				break;		   			case 2:		   				number="This is two";		   				break;		   			case 3:		   				number="This is three";		   				break;		   			case 4:		   				number="This is four";		   				break;		   		}			  el = document.getElementById("message");			  el.innerHTML = number;		  }		function picture_sub()		  {				  if (image>0)					  {					  image--;				  }			  switch (image)		   		{		   			case 0:		   				number="<font style='color: red;'>This is zero </font>";		   				break;		   			case 1:		   				number="This is one";		   				break;		   			case 2:		   				number="This is two";		   				break;		   			case 3:		   				number="This is three";		   				break;		   			case 4:		   				number="This is four";		   				break;		   		}			  el = document.getElementById("message");			  el.innerHTML = number;		  }	</script></head><body>	<div id="heading">		<h1>BLACK</h1>	</div>		<div>		<font class="arrow" onclick="picture_sub()"><</font>	   <font id="message"></font>	   <font class="arrow" onclick="picture_add()">></font>	</div></body></html>

Thanks in advance :)

Share this post


Link to post
Share on other sites

Yup. Very similar functions can be combined if you pass a flag that tells the function where to make changes. In this case, I used the value of the flag as well. You'll notice I changed your <font> tags to <span> tags since <font> is deprecated. I also took out the inline style and created a class. You may be puzzled by the ternary operators (the one with the ?). Try reading up on them if you don't understand, or ask and I'll explain. When you get used to them, they can be more natural to read than if/else statements, and they take up less space.

<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01//EN"   "http://www.w3.org/TR/html4/strict.dtd"><html>	<head>		<meta http-equiv="content-type" content="text/html;charset=iso-8859-1">		<title></title>		<style type="text/css">			.red {				color: #ee0000;			}		</style>		<script type="text/javascript">			var image = 0;			var number = "";			function change_picture(i) {				image += i;				i == 1  && image > 4 ? image = 0 : null;				i == -1 && image < 0 ? image = 4 : null;				switch (image) {					case 0:						number = (i == -1) ? "<span class='red'>This is zero</span>" : "This is zero";						break;					case 1:						number="This is one";						break;					case 2:						number="This is two";						break;					case 3:						number="This is three";						break;					case 4:						number="This is four";						break;				}				el = document.getElementById("message");				el.innerHTML = number;			}		</script>	</head>	<body>		<div id="heading">			<h1>BLACK</h1>		</div>		<div>			<span class="arrow" onclick="change_picture(-1)">< </span>			<span id="message"></span>			<span class="arrow" onclick="change_picture(1)"> ></span>		</div>	</body></html>

Share this post


Link to post
Share on other sites

Thanks!That works even better than my way :)I like the way if you keep clicking one arrow, it will loop.Thanks for all the help, I'll let you know if I can't figure out part of it. :)

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
Sign in to follow this  

×