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            <font color="#2040a0">exit</font><font color="4444FF">(</font><font color="#FF0000">1</font><font color="4444FF">)</font><font color="4444FF">;</font>
        <font color="4444FF"><strong>}</strong></font>

        <font color="#444444">// Convert read side of pipe to string and pass as an argument </font>
        <font color="#444444">// to the child process.</font>
        <font color="#2040a0">itoa</font><font color="4444FF">(</font><font color="#2040a0">hpipe</font><font color="4444FF">[</font><font color="#2040a0">READ</font><font color="4444FF">]</font>, <font color="#2040a0">hstr</font>, <font color="#FF0000">10</font><font color="4444FF">)</font><font color="4444FF">;</font>
        <strong>if</strong> <font color="4444FF">(</font><font color="4444FF">(</font><font color="#2040a0">pid</font> <font color="4444FF">=</font> <font color="#2040a0">spawnl</font><font color="4444FF">(</font><font color="#2040a0">P_NOWAIT</font>, <font color="#2040a0">argv</font><font color="4444FF">[</font><font color="#FF0000">0</font><font color="4444FF">]</font>, <font color="#2040a0">argv</font><font color="4444FF">[</font><font color="#FF0000">0</font><font color="4444FF">]</font>, <font color="#2040a0">hstr</font>, <font color="#2040a0">NULL</font><font color="4444FF">)</font><font color="4444FF">)</font> <font color="4444FF">=</font><font color="4444FF">=</font> <font color="4444FF">-</font><font color="#FF0000">1</font><font color="4444FF">)</font> <font color="4444FF"><strong>{</strong></font>
            <font color="#2040a0">perror</font><font color="4444FF">(</font><font color="#008000">&quot;Spawn failed&quot;</font><font color="4444FF">)</font><font color="4444FF">;</font>
        <font color="4444FF"><strong>}</strong></font>

        <font color="#444444">// Put problem in write pipe; it will appear in child's read pipe.</font>
        <strong>for</strong> <font color="4444FF">(</font><font color="#2040a0">problem</font> <font color="4444FF">=</font> <font color="#FF0000">1000</font><font color="4444FF">;</font> <font color="#2040a0">problem</font> <font color="4444FF">&lt;</font><font color="4444FF">=</font> <font color="#2040a0">NUMPROBLEM</font> <font color="4444FF">*</font> <font color="#FF0000">1000</font><font color="4444FF">;</font> <font color="#2040a0">problem</font> <font color="4444FF">+</font><font color="4444FF">=</font> <font color="#FF0000">1000</font><font color="4444FF">)</font> <font color="4444FF"><strong>{</strong></font>
            <strong>if</strong> <font color="4444FF">(</font><font color="#2040a0">write</font><font color="4444FF">(</font><font color="#2040a0">hpipe</font><font color="4444FF">[</font><font color="#2040a0">WRITE</font><font color="4444FF">]</font>, <font color="4444FF">(</font><strong>char</strong> <font color="4444FF">*</font><font color="4444FF">)</font> <font color="4444FF">&amp;</font><font color="#2040a0">problem</font>, <strong>sizeof</strong><font color="4444FF">(</font><strong>int</strong><font color="4444FF">)</font><font color="4444FF">)</font> <font color="4444FF">=</font><font color="4444FF">=</font> <font color="4444FF">-</font><font color="#FF0000">1</font><font color="4444FF">)</font> <font color="4444FF"><strong>{</strong></font>
                <font color="#2040a0">perror</font><font color="4444FF">(</font><font color="#008000">&quot;parent write failed&quot;</font><font color="4444FF">)</font><font color="4444FF">;</font>
            <font color="4444FF"><strong>}</strong></font>
            <strong>else</strong> <font color="4444FF"><strong>{</strong></font>
                <font color="#2040a0">printf</font><font color="4444FF">(</font><font color="#008000">&quot;Son, what is the square root of %d?<font color="#77dd77">\n</font>&quot;</font>, <font color="#2040a0">problem</font><font color="4444FF">)</font><font color="4444FF">;</font>
            <font color="4444FF"><strong>}</strong></font>
        <font color="4444FF"><strong>}</strong></font>

        <font color="#444444">// Wait until spawned program is done processing.</font>
        <font color="#2040a0">CWAIT</font><font color="4444FF">(</font><font color="4444FF">&amp;</font><font color="#2040a0">termstat</font>, <font color="#2040a0">pid</font>, <font color="#2040a0">WAIT_CHILD</font><font color="4444FF">)</font><font color="4444FF">;</font>
        <strong>if</strong> <font color="4444FF">(</font><font color="#2040a0">termstat</font> <font color="4444FF">&amp;</font> <font color="#FF0000">0x0</font><font color="4444FF">)</font> <font color="4444FF"><strong>{</strong></font>
            <font color="#2040a0">perror</font><font color="4444FF">(</font><font color="#008000">&quot;Child failed&quot;</font><font color="4444FF">)</font><font color="4444FF">;</font>
        <font color="4444FF"><strong>}</strong></font>

        <font color="#2040a0">close</font><font color="4444FF">(</font><font color="#2040a0">hpipe</font><font color="4444FF">[</font><font color="#2040a0">READ</font><font color="4444FF">]</font><font color="4444FF">)</font><font color="4444FF">;</font>
        <font color="#2040a0">close</font><font color="4444FF">(</font><font color="#2040a0">hpipe</font><font color="4444FF">[</font><font color="#2040a0">WRITE</font><font color="4444FF">]</font><font color="4444FF">)</font><font color="4444FF">;</font>
    <font color="4444FF"><strong>}</strong></font>
    <strong>else</strong> <font color="4444FF"><strong>{</strong></font>
        <font color="#444444">//// There is a command line argument, so we must be a child process</font>
        <font color="#444444">// Convert argument to integer handle value.</font>
        <font color="#2040a0">hpipe</font><font color="4444FF">[</font><font color="#2040a0">READ</font><font color="4444FF">]</font> <font color="4444FF">=</font> <font color="#2040a0">atoi</font><font color="4444FF">(</font><font color="#2040a0">argv</font><font color="4444FF">[</font><font color="#FF0000">1</font><font color="4444FF">]</font><font color="4444FF">)</font><font color="4444FF">;</font>

        <font color="#444444">// Read problem from pipe and calculate solution.</font>
        <strong>for</strong> <font color="4444FF">(</font><font color="#2040a0">c</font> <font color="4444FF">=</font> <font color="#FF0000">0</font><font color="4444FF">;</font> <font color="#2040a0">c</font> <font color="4444FF">&lt;</font> <font color="#2040a0">NUMPROBLEM</font><font color="4444FF">;</font> <font color="#2040a0">c</font><font color="4444FF">+</font><font color="4444FF">+</font><font color="4444FF">)</font> <font color="4444FF"><strong>{</strong></font>
            <strong>if</strong> <font color="4444FF">(</font><font color="#2040a0">read</font><font color="4444FF">(</font><font color="#2040a0">hpipe</font><font color="4444FF">[</font><font color="#2040a0">READ</font><font color="4444FF">]</font>, <font color="4444FF">(</font><strong>char</strong> <font color="4444FF">*</font><font color="4444FF">)</font> <font color="4444FF">&amp;</font><font color="#2040a0">problem</font>, <strong>sizeof</strong><font color="4444FF">(</font><strong>int</strong><font color="4444FF">)</font><font color="4444FF">)</font> <font color="4444FF">=</font><font color="4444FF">=</font> <font color="4444FF">-</font><font color="#FF0000">1</font><font color="4444FF">)</font> <font color="4444FF"><strong>{</strong></font>
                <font color="#2040a0">perror</font><font color="4444FF">(</font><font color="#008000">&quot;child read failed&quot;</font><font color="4444FF">)</font><font color="4444FF">;</font>
            <font color="4444FF"><strong>}</strong></font>
            <strong>else</strong> <font color="4444FF"><strong>{</strong></font>
                <font color="#2040a0">printf</font><font color="4444FF">(</font><font color="#008000">&quot;Dad, the square root of %d is %3.2f.<font color="#77dd77">\n</font>&quot;</font>, <font color="#2040a0">problem</font>,
                       <font color="#2040a0">sqrt</font><font color="4444FF">(</font><font color="4444FF">(</font><strong>double</strong><font color="4444FF">)</font> <font color="#2040a0">problem</font><font color="4444FF">)</font><font color="4444FF">)</font><font color="4444FF">;</font>
            <font color="4444FF"><strong>}</strong></font>
        <font color="4444FF"><strong>}</strong></font>
    <font color="4444FF"><strong>}</strong></font>

    <strong>return</strong> <font color="#FF0000">0</font><font color="4444FF">;</font>
<font color="4444FF"><strong>}</strong></font>
</pre>

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			<i>Last modified on 29 April 2000 at 15:52 UTC-7</i>
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