yabasic.htm

一个小巧的BASIC解释器的源代码很小可它的确做到了

        file should have the extension ".yab".
        Double-click on this file then invokes yabasic, to
        execute your program. </td>
    </tr>
</table>

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<hr>

<h2><a name="Options, Windows">Options</a></h2>

<dl>
    <dt><code><strong>-h</strong></code><strong> </strong></dt>
    <dd>Prints out a short help message; <code><strong>-help</strong></code>
        or <code><strong>-?</strong></code> are accepted as well.
    </dd>
    <dt><code><strong>-geometry</strong></code><strong> </strong><font
        face="Times New Roman"><em><strong><var>geometry-string</var></strong></em></font>
    </dt>
    <dd>E.g. <code><strong>+20+10</strong></code> will place the
        graphic-window 10 pixels below and 20 pixels left of the
        upper left corner of the screen.</dd>
    <dt><code><strong>-font</strong></code><strong> </strong><font
        face="Times New Roman"><em><strong><var>Name-of-font</var></strong></em></font></dt>
    <dd>Name of the font which will be used for graphics text.
        Can be any of: <br>
        <code><strong>decorative, dontcare, modern, roman,
        script, swiss</strong></code> <br>
        You can append (without space) a fontsize to any of these
        identifiers, i.e. <font face="Courier New"><strong>swiss30</strong></font>
        chooses a swiss font, 30 pixels high.</dd>
    <dt><code><strong>-i</strong></code></dt>
    <dd>Sets the initial <a name="infolevel">infolevel</a>. This
        controls the amount of information one gets about the
        progress of program execution, Every level contains all
        lower levels (e.g. <code><strong>w</strong></code>
        contains <code><strong>f</strong></code> and <code><strong>e</strong></code>)
        and can be one of: <dl>
            <dt><code><strong>d</strong></code><strong> </strong></dt>
            <dd>Set the inoflevel to <em><strong>diagnostic</strong></em><em>
                </em>: This gives detailed debugging information;
                much more output than you'd probably like to
                read. </dd>
            <dt><code><strong>n</strong></code></dt>
            <dd><em><strong>note</strong></em><em> </em>: Useful
                information; e.g. about execution time and memory
                consumption. </dd>
            <dt><code><strong>w</strong></code> </dt>
            <dd><em><strong>warning</strong></em><em> </em>:
                Gives you warnings, that something has gone wrong
                (e.g. division by zero); nevertheless execution
                proceeds. </dd>
            <dt><code><strong>e</strong></code> </dt>
            <dd><em><strong>error</strong></em><em> </em>: A
                serious error (e.g. an array boundary violation)
                has occurred, stopping the program. </dd>
            <dt><code><strong>f</strong></code> </dt>
            <dd><em><strong>fatal</strong></em><em> </em>:
                Something has gone wrong and cannot be fixed; the
                interpreter exits immediately. This happens most
                often in the course of an arithmetic fault
                (floating point exception) but can also be a sign
                of an internal error within yabasic. </dd>
        </dl>
        <p>The default infolevel is <code><strong>w</strong></code>.
        </p>
    </dd>
    <dt><font face="Courier New"><strong>-licence</strong></font></dt>
    <dd>This makes yabasic print out its copyleft; have a look
        and you will see, that almost anything is allowed.</dd>
</dl>

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<hr>

<h2><a name="Setting defaults, Windows">Setting defaults</a></h2>

<p>To choose the default-values for graphic-font, fontsize and
window position, you have to edit the registry.</p>

<p>Yabasic stores its defaults under:</p>

<blockquote>
    <p><font face="Courier New"><strong>HKEY_LOCAL_MACHINE/SOFTWARE/Yabasic</strong></font></p>
</blockquote>

<p>You may edit the subkeys &quot;font&quot; and
&quot;geometry&quot;; these subkeys accept the same values as the
corresponding <a href="#Options, Windows">command line options</a>
<font face="Courier New"><strong>-font</strong></font> and <font
face="Courier New"><strong>-geometry</strong></font>. Command
line options take precedence over registry defaults.</p>

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<hr>

<h1><a name="Yabasic described by examples">Yabasic explained by
examples</a></h1>

<h2><a name="A simple Program">A simple Program</a></h2>

<p>This is the first example:</p>

<blockquote>
    <pre><strong>REM this is the first yabasic-program
input &quot;Enter two numbers:&quot; a,b
print a,&quot;+&quot;,b,&quot;=&quot;,a+b
print &quot;Please enter your Name:&quot;;
INPUT a$
print &quot;Hello &quot;,a$,&quot; !&quot;</strong></pre>
</blockquote>

<p>This program produces the following output (user input is
displayed like <font face="Courier New"><em><strong><u>this</u></strong></em></font>):</p>

<blockquote>
    <pre><strong>Enter two numbers: </strong><font
color="#000000"><em><strong><u>2 3</u></strong></em></font><strong>
2+3=5
Please enter your Name: </strong><em><strong><u>Bill</u></strong></em><strong>
Hello Bill !</strong></pre>
</blockquote>

<p>This simple program contains three different commands:</p>

<dl>
    <dt><a name="REM"><font face="Courier New"><strong>REM</strong></font></a></dt>
    <dd>The <font face="Courier New"><strong>REM</strong></font>-statement
        introduces comments; everything after <font
        face="Courier New"><strong>REM</strong></font> up to the
        end of the line is ignored.</dd>
    <dt><a name="input"><font face="Courier New"><strong>input</strong></font></a></dt>
    <dd>This statement reads one or more variables from the user.
        The optional prompt-string after the <font
        face="Courier New"><strong>input</strong></font>-statement
        (<font face="Courier New">&quot;<strong>Enter a number:</strong>&quot;</font>)
        is printed on the terminal prior to reading any input.
        Note that there is no semicolon after this prompt-string.
        To learn more about, how input chops a line into pieces
        you may refer to the section <a href="#More on input">More
        on Input</a>. To learn, how to read input from the
        keyboard without delay, check out <a
        href="#Getting a key from the keyboard">Getting a key
        from the keyboard</a>.</dd>
    <dt><a name="print"><font face="Courier New"><strong>print</strong></font></a></dt>
    <dd>The print-statement writes all its arguments to the
        screen; after writing its last argument, <font
        face="Courier New"><strong>print</strong></font> goes to
        the next line (as in<font face="Courier New"> <strong>print
        &quot;Hello &quot;,a$,&quot; !&quot;</strong></font>); to
        avoid this automatic newline, place a colon after the
        last argument (as in<font face="Courier New"> <strong>print
        &quot;Please enter your Name:&quot;;</strong></font>).
        Note that print can be abbreviated with a single question
        mark (?). If you want to print (or input) at a specific
        location, you may go to the section <a
        href="#Printing at a Random Position">Prining on your
        Screen</a>.</dd>
</dl>

<p>Furthermore some general properties of yabasic should be
noted:</p>

<dl>
    <dt><a name="Case"><strong>Case</strong></a></dt>
    <dd>Commands can be entered in any case: <font
        face="Courier New"><strong>input</strong></font> is the
        same as <font face="Courier New"><strong>INPUT</strong></font>
        and even as <font face="Courier New"><strong>InPUt</strong></font><strong>.
        This applies to every command in yabasic but not to
        variables, i.e. </strong><font face="Courier New"><strong>a$</strong></font><strong>
        and </strong><font face="Courier New"><strong>A$</strong></font><strong>
        are different variables.</strong></dd>
    <dt><a name="Variables"><strong>Variables</strong></a></dt>
    <dd>Variable names are case sensitive (i.e. types of
        variables: <font face="Courier New"><strong>a$</strong></font>
        and <font face="Courier New"><strong>A$</strong></font>
        are different) and can be of any length. There are two
        sorts of variables:</dd>
    <dt>&nbsp;</dt>
    <dd><dl>
            <dt>String variables</dt>
            <dd>e.g.<font face="Courier New"> <strong>a$</strong></font>,
                <font face="Courier New"><strong>b12$</strong></font>
                or <font face="Courier New"><strong>VeryLongName$</strong>
                </font>may contain strings of any length. String
                variables always have a Dollar-sign (<font
                face="Courier New"><strong>$</strong></font>) as
                the last character of their names.</dd>
            <dt>Numerical variables</dt>
            <dd>e.g. <font face="Courier New"><strong>a</strong></font>,
                <font face="Courier New"><strong>c3po</strong></font>
                or <font face="Courier New"><strong>ThisIsAnEvenLongerName</strong></font>
                contain real numbers like 2, -1.3, 15.3e44 or 0.</dd>
        </dl>
        <p>Variables (with the exception of arrays) need not be
        declared, their initial values are &quot;&quot; (for
        string variables) and 0.0 (for numerical variables).</p>
    </dd>
</dl>

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<hr>

<h2><a name="Arithmetic">Arithmetic</a></h2>

<h3><a name="Operators">Operators</a></h3>

<p>Yabasic has five arithmetic operators: <font
face="Courier New"><strong>+</strong></font> (addition), <font
face="Courier New"><strong>-</strong></font> (subtraction), <font
face="Courier New"><strong>*</strong></font> (multiplication), <font
face="Courier New"><strong>/</strong></font><strong> </strong>(division)
and <font face="Courier New"><strong>^</strong></font> (power);
they all behave as expected, i.e. this line of code</p>

<blockquote>
    <pre><strong>print 1+2,2*3,4/2,2^3</strong></pre>
</blockquote>

<p>produces this line of output:</p>

<blockquote>
    <pre><strong>3 6 2 8</strong></pre>
</blockquote>

<p>Note that the power operator (<font face="Courier New"><strong>^</strong></font>)
handles fractional powers: <font face="Courier New"><strong>8^(1/3)</strong></font>
gives <font face="Courier New"><strong>2</strong></font> as a
result.</p>

<h3><a name="Functions">Functions</a></h3>

<p>This section demonstrates and explains the arithmetic
functions of yabasic.</p>

<dl>
    <dt><a name="Trigonometric functions:"><strong>Trigonometric
        functions:</strong></a></dt>
    <dd>There are 6 trigonometric functions:<dl>
            <dd><pre><strong>print sin(1.0),cos(pi),tan(3)
print asin(0.5),acos(0.7)
print atan(2),atan(1,2)</strong></pre>
            </dd>
        </dl>
    </dd>
    <dd>These lines produce this output:<dl>
            <dd><pre><strong>0.841471 -1 -0.142547
0.523599 0.795399
1.10715 0.463648</strong></pre>
            </dd>
        </dl>
    </dd>
    <dd>As you can see yabasic can calculate sine, cosine,
        tangent and their inverses. And, if you have an eye for
        trigonometry, you may have noticed that all these
        functions expect their argument in radians; to facilitate
        the transformation from degrees to radians (<font
        face="Courier New"><strong>radian=degree*pi/180</strong></font>),
        there is a predefined variable named <font
        face="Courier New"><strong>pi</strong></font> (or <font
        face="Courier New"><strong>PI</strong></font>) which has
        an initial value of 3.14159.</dd>
</dl>