simple04.html

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title: Simple HTML - Introducing variables
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		<h1>Introducing variables</h1>
		<p>When you write programs you often need to give the computer
			information to work on. The computer stores this
			information in spaces called variables
			in its memory.</p>
		<center><img src="{{ base_uri }}/img/usborne/simple-basic/img/05boxes.jpg"></center>
		<p>The spaces in the computer's memory are rather like the empty boxes in this picture.
			When you give the computer a piece of information you have to give it a label too.
			The computer puts information in a space and labels it.
			A labelled space is called a variable.</p>
	
		<p>Type in the following line:</p>
<pre>
N=999
</pre>
		<p>The letter <code>N</code> is the label for the variable, and <code>999</code> is the value to
		be stored in a variable labelled <code>N</code>.</p>
		<p>You might sometimes see this written <code>LET N=999</code>. You can leave out the <code>LET</code> on this computer.</p>

		<aside>
			<p>Note that here we're not writing a program, because there are no line numbers. This means that the computer immediately
				runs the instruction we've typed.
			</p>
		</aside>

		<p>Now let’s <code class="command">PRINT</code> out the value in the variable <code>N</code>:</p>
<pre>
PRINT N
</pre>
		<p>You will see the number <code>999</code> printed out.</p>
		<p>Try changing the value stored in <code>N</code> by typing the first line again, but
		this time with a different number, and then <code class="command">PRINT</code> it out again.</p>

		<h2>Strings</h2>
		<p>In BASIC, words, letters and symbols are called <em>strings</em>. When you store a string in a variable,
			you must type the string in quotes. A variable
			that contains a string is called a <em>string variable</em>.
			Its label always has a dollar sign at the end.</p>
<pre>
U$="UGLY MONSTER"
R$="RUBBISH"
S$="/&SILLY SYMBOLS!!"
</pre>
		<p>String variable labels always end with a <code>$</code>. Variables that <em>don’t</em>
		end with a <code>$</code>, like <code>N</code> above, are <em>numeric</em> variables. They
		store numbers such as <code>42</code> or even <code>3.14</code>.</p>

		<h2>Using <code class="command">PRINT</code> with variables</h2>
		<p>To make the computer display the information stored in a
			variable, you use <code class="command">PRINT</code> followed by the variable name.
			Try running the program below to see how this works.</p>
<pre>
NEW
10 CLS
20 N=99
30 B$="BANANAS"
40 PRINT N
50 PRINT B$
RUN
</pre>

		<h2>Naming variables</h2>
		<p>It's a good idea to give a variable a name that will
			help you remember what it contains.</p>
		<center><img src="{{ base_uri }}/img/usborne/simple-basic/img/05naming.jpg"></center>
		<p>Letters of the alphabet and words are usually used as names for variables.
			You can also use numbers, as long as the variable name <em>starts</em> with a letter.</p>
		
		<p>So rather than the single letter variable names we used above, it is easier to understand if we use longer names like:</p>

<pre>
NEW
10 CLS
20 QUANTITY=99
30 FRUIT$="BANANAS"
40 PRINT QUANTITY; FRUIT$
RUN
</pre>

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