Web Development Tutorials


Do-While Loops

The do...while statement loops through a block of code as long as a specified condition is evaluated as true. In other words, the while statement will execute a block of code if and as long as a condition is true.

The do...while loop is similar in nature to the while loop discussed in the previous section. The key difference is that the do...while loop body is guaranteed to run at least once. This is possible because the condition statement is evaluated at the end of the loop statement after the loop body is performed.

The basic do...while loop syntax is shown below:

do {
     code to be executed;
} while (condition);

The code within a while loop will repeatedly execute as long as the condition at the end of the loop evaluates to true. The code block associated with the while statement is always enclosed within the { opening and } closing brace symbols.

The following example demonstrates a while loop that continues to execute as long as the variable $number is greater than or equal to 2:

$number = 5;
do {
     echo $number . "<br/>";
     $number -= 1;
} while ($number >= 2);	

In the above example, the variable $number is initialized to 5. The do...while loop executes as long as the condition, ($number >=2), or $number is greater than or equal to 2, printing the value of $number to the browser window. At the end of the loop block, the value of $number is decreased by 1.

Below is the output generated by the sample loop:


During the first run, the value of $number is equal to 5. Since the condition of the loop is not checked until after the loop has run once, the value of $number, 5 is displayed. Next, the value of $number is decremented by 1, becoming 4. Since 4 is greater than 2, the loop runs again and during the second iteration the echo statement is used to display the value 4. A <br> is concatenated to the display to create a carriage return each time the loop is processed. This process continues while the value of $number is 3 and 2. When $number is equal to 2, the echo statement displays the value 2 and the value of $number is then decremented to 1. Since 1 is not greater than or equal to 2, the condition is no longer true and the while loop ends.

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