<html lang="en"> <head> <title>The while Statement - GNU Octave</title> <meta http-equiv="Content-Type" content="text/html"> <meta name="description" content="GNU Octave"> <meta name="generator" content="makeinfo 4.13"> <link title="Top" rel="start" href="index.html#Top"> <link rel="up" href="Statements.html#Statements" title="Statements"> <link rel="prev" href="The-switch-Statement.html#The-switch-Statement" title="The switch Statement"> <link rel="next" href="The-do_002duntil-Statement.html#The-do_002duntil-Statement" title="The do-until Statement"> <link href="http://www.gnu.org/software/texinfo/" rel="generator-home" title="Texinfo Homepage"> <meta http-equiv="Content-Style-Type" content="text/css"> <style type="text/css"><!-- pre.display { font-family:inherit } pre.format { font-family:inherit } pre.smalldisplay { font-family:inherit; font-size:smaller } pre.smallformat { font-family:inherit; font-size:smaller } pre.smallexample { font-size:smaller } pre.smalllisp { font-size:smaller } span.sc { font-variant:small-caps } span.roman { font-family:serif; font-weight:normal; } span.sansserif { font-family:sans-serif; font-weight:normal; } --></style> </head> <body> <div class="node"> <a name="The-while-Statement"></a> <p> Next: <a rel="next" accesskey="n" href="The-do_002duntil-Statement.html#The-do_002duntil-Statement">The do-until Statement</a>, Previous: <a rel="previous" accesskey="p" href="The-switch-Statement.html#The-switch-Statement">The switch Statement</a>, Up: <a rel="up" accesskey="u" href="Statements.html#Statements">Statements</a> <hr> </div> <h3 class="section">10.3 The while Statement</h3> <p><a name="index-g_t_0040code_007bwhile_007d-statement-698"></a><a name="index-g_t_0040code_007bendwhile_007d-statement-699"></a><a name="index-loop-700"></a><a name="index-body-of-a-loop-701"></a> In programming, a <dfn>loop</dfn> means a part of a program that is (or at least can be) executed two or more times in succession. <p>The <code>while</code> statement is the simplest looping statement in Octave. It repeatedly executes a statement as long as a condition is true. As with the condition in an <code>if</code> statement, the condition in a <code>while</code> statement is considered true if its value is non-zero, and false if its value is zero. If the value of the conditional expression in a <code>while</code> statement is a vector or a matrix, it is considered true only if it is non-empty and <em>all</em> of the elements are non-zero. <p>Octave's <code>while</code> statement looks like this: <pre class="example"> while (<var>condition</var>) <var>body</var> endwhile </pre> <p class="noindent">Here <var>body</var> is a statement or list of statements that we call the <dfn>body</dfn> of the loop, and <var>condition</var> is an expression that controls how long the loop keeps running. <p>The first thing the <code>while</code> statement does is test <var>condition</var>. If <var>condition</var> is true, it executes the statement <var>body</var>. After <var>body</var> has been executed, <var>condition</var> is tested again, and if it is still true, <var>body</var> is executed again. This process repeats until <var>condition</var> is no longer true. If <var>condition</var> is initially false, the body of the loop is never executed. <p>This example creates a variable <code>fib</code> that contains the first ten elements of the Fibonacci sequence. <pre class="example"> fib = ones (1, 10); i = 3; while (i <= 10) fib (i) = fib (i-1) + fib (i-2); i++; endwhile </pre> <p class="noindent">Here the body of the loop contains two statements. <p>The loop works like this: first, the value of <code>i</code> is set to 3. Then, the <code>while</code> tests whether <code>i</code> is less than or equal to 10. This is the case when <code>i</code> equals 3, so the value of the <code>i</code>-th element of <code>fib</code> is set to the sum of the previous two values in the sequence. Then the <code>i++</code> increments the value of <code>i</code> and the loop repeats. The loop terminates when <code>i</code> reaches 11. <p>A newline is not required between the condition and the body; but using one makes the program clearer unless the body is very simple. </body></html>