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<a name="Numerical-input-and-output"></a>
<p>
Previous:&nbsp;<a rel="previous" accesskey="p" href="Numerical-operations.html#Numerical-operations">Numerical operations</a>,
Up:&nbsp;<a rel="up" accesskey="u" href="Numbers.html#Numbers">Numbers</a>
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</div>

<h4 class="subsection">6.2.6 Numerical input and output</h4>

<p><a name="index-g_t_0040w_007bnumerical-input-and-output_007d-291"></a>

<div class="defun">
&mdash; procedure: <b>number-&gt;string</b><var> z<a name="index-number_002d_003estring-292"></a></var><br>
&mdash; procedure: <b>number-&gt;string</b><var> z radix<a name="index-number_002d_003estring-293"></a></var><br>
<blockquote>
     <p><var>Radix</var> must be an exact integer, either 2, 8, 10, or 16.  If omitted,
<var>radix</var> defaults to 10. 
The procedure &lsquo;<samp><span class="samp">number-&gt;string</span></samp>&rsquo; takes a
number and a radix and returns as a string an external representation of
the given number in the given radix such that

     <pre class="format"><tt>(let ((number </tt><var>number</var><tt>)
           (radix </tt><var>radix</var><tt>))
       (eqv? number
             (string-&gt;number (number-&gt;string number
                                             radix)
                             radix)))
     </tt>
</pre>
     <p>is true.  It is an error if no possible result makes this expression true.

     <p>If <var>z</var> is inexact, the radix is 10, and the above expression
can be satisfied by a result that contains a decimal point,
then the result contains a decimal point and is expressed using the
minimum number of digits (exclusive of exponent and trailing
zeroes) needed to make the above expression
true [howtoprint], [howtoread];
otherwise the format of the result is unspecified.

     <p>The result returned by &lsquo;<samp><span class="samp">number-&gt;string</span></samp>&rsquo;
never contains an explicit radix prefix.

     <blockquote>
<em>Note:</em>
The error case can occur only when <var>z</var> is not a complex number
or is a complex number with a non-rational real or imaginary part. 
</blockquote>

     <blockquote>
<em>Rationale:</em>
If <var>z</var> is an inexact number represented using flonums, and
the radix is 10, then the above expression is normally satisfied by
a result containing a decimal point.  The unspecified case
allows for infinities, NaNs, and non-flonum representations. 
</blockquote>

     </blockquote></div>

<div class="defun">
&mdash; procedure: <b>string-&gt;number</b><var> string<a name="index-string_002d_003enumber-294"></a></var><br>
&mdash; procedure: <b>string-&gt;number</b><var> string radix<a name="index-string_002d_003enumber-295"></a></var><br>
<blockquote>
     <!-- %R4%% I didn't include the (string->number string radix exactness) -->
     <!-- case, since I haven't heard any resolution of the coding to be used -->
     <!-- for the third argument. -->
     <p>Returns a number of the maximally precise representation expressed by the
given <var>string</var>.  <var>Radix</var> must be an exact integer, either 2, 8, 10,
or 16.  If supplied, <var>radix</var> is a default radix that may be overridden
by an explicit radix prefix in <var>string</var> (e.g. <tt>"#o177"</tt>).  If <var>radix</var>
is not supplied, then the default radix is 10.  If <var>string</var> is not
a syntactically valid notation for a number, then &lsquo;<samp><span class="samp">string-&gt;number</span></samp>&rsquo;
returns <tt>#f</tt>.

     <pre class="format"><tt>(string-&gt;number "100")                 ==&gt;  100
     (string-&gt;number "100" 16)              ==&gt;  256
     (string-&gt;number "1e2")                 ==&gt;  100.0
     (string-&gt;number "15##")                ==&gt;  1500.0
     </tt>
</pre>
     <blockquote>
<em>Note:</em>
The domain of &lsquo;<samp><span class="samp">string-&gt;number</span></samp>&rsquo; may be restricted by implementations
in the following ways.  &lsquo;<samp><span class="samp">String-&gt;number</span></samp>&rsquo; is permitted to return
<tt>#f</tt> whenever <var>string</var> contains an explicit radix prefix. 
If all numbers supported by an implementation are real, then
&lsquo;<samp><span class="samp">string-&gt;number</span></samp>&rsquo; is permitted to return <tt>#f</tt> whenever
<var>string</var> uses the polar or rectangular notations for complex
numbers.  If all numbers are integers, then
&lsquo;<samp><span class="samp">string-&gt;number</span></samp>&rsquo; may return <tt>#f</tt> whenever
the fractional notation is used.  If all numbers are exact, then
&lsquo;<samp><span class="samp">string-&gt;number</span></samp>&rsquo; may return <tt>#f</tt> whenever
an exponent marker or explicit exactness prefix is used, or if
a <tt>#</tt> appears in place of a digit.  If all inexact
numbers are integers, then
&lsquo;<samp><span class="samp">string-&gt;number</span></samp>&rsquo; may return <tt>#f</tt> whenever
a decimal point is used. 
</blockquote>

     </blockquote></div>

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