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<h3 class="section" id="The-do_002duntil-Statement-1"><span>10.4 The do-until Statement<a class="copiable-link" href="#The-do_002duntil-Statement-1"> ¶</a></span></h3>
<a class="index-entry-id" id="index-do_002duntil-statement"></a>
<p>The <code class="code">do-until</code> statement is similar to the <code class="code">while</code> statement,
except that it repeatedly executes a statement until a condition becomes
true, and the test of the condition is at the end of the loop, so the
body of the loop is always executed at least once. As with the
condition in an <code class="code">if</code> statement, the condition in a <code class="code">do-until</code>
statement is considered true if its value is nonzero, and false if its
value is zero. If the value of the conditional expression in a
<code class="code">do-until</code> statement is a vector or a matrix, it is considered
true only if it is non-empty and <em class="emph">all</em> of the elements are nonzero.
</p>
<p>Octave’s <code class="code">do-until</code> statement looks like this:
</p>
<div class="example">
<div class="group"><pre class="example-preformatted">do
<var class="var">body</var>
until (<var class="var">condition</var>)
</pre></div></div>
<p>Here <var class="var">body</var> is a statement or list of statements that we call the
<em class="dfn">body</em> of the loop, and <var class="var">condition</var> is an expression that
controls how long the loop keeps running.
</p>
<p>This example creates a variable <code class="code">fib</code> that contains the first ten
elements of the Fibonacci sequence.
</p>
<div class="example">
<div class="group"><pre class="example-preformatted">fib = ones (1, 10);
i = 2;
do
i++;
fib (i) = fib (i-1) + fib (i-2);
until (i == 10)
</pre></div></div>
<p>A newline is not required between the <code class="code">do</code> keyword and the
body; but using one makes the program clearer unless the body is very
simple.
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