10.4 The do-until Statement

The `do-until` statement is similar to the `while` 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 `if` statement, the condition in a `do-until` 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 `do-until` statement is a vector or a matrix, it is considered true only if it is non-empty and all of the elements are nonzero.

Octave’s `do-until` statement looks like this:

```do
body
until (condition)
```

Here body is a statement or list of statements that we call the body of the loop, and condition is an expression that controls how long the loop keeps running.

This example creates a variable `fib` that contains the first ten elements of the Fibonacci sequence.

```fib = ones (1, 10);
i = 2;
do
i++;
fib (i) = fib (i-1) + fib (i-2);
until (i == 10)
```

A newline is not required between the `do` keyword and the body; but using one makes the program clearer unless the body is very simple.