Tutorials - PHP - Loops I - The FOR Loop

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Loops I - The for Loop

Tutorials > PHP > Loops I - The FOR Loop

What Are Loops?

Often you may need to execute the same block of code several times consecutively. Loops provide a convenient structure in which to do this.

The for Loop

A for is usually used to execute a block of code a specified number of times. The basic structure of a for loop is:

for ( initialization ; condition ; counter ) {
    //Do something.
}

The for loop takes three parameters:

initialization - An expression which will be run once before the loop begins. Usually, this is used to assign an intial value to a counter.
condition - An expression which is evaluated before each iteration of the loop. If the expression is true, the loop will continue running, otherwise it will stop and the flow of execution will continue with the next section of code outside the loop.
counter - An expression which is run after each iteration of the loop. This is normally used to increment a counter variable.

This code:

for ( $i=1 ; $i<=10 ; $i++ ) {
    echo("$i<br>");
}

Produces the following result:

1
2
3
4
5
6
7
8
9
10

So, what's going on here?

PHP runs the initialization - in this case, assigning a value of 1 to $i.
Check the condition. If $i is less than or equal to 10, i.e. the condition statement is true, the echo() statement is run.
Run the counter code. In this case, $i is incremented by one.
Return to step 2.

The process continues until, at step 2, the condition statement is no longer true. At this point, the loop finishes, and execution continues with the statement below.

Note that each of the 3 parameters to the for loop is optional. Both of the following examples are valid in PHP:

for ( ; ; ) {
    $i++;
    echo("$i<br>");
}

for( ; ; $i++) {
    echo("$i<br>");
}

These will both produce the same result - an infinite loop, which will continue incrementing $i and outputting its value until the user stops the script manually.

The foreach Loop

A foreach loop iterates through each item in an array. It can take one of two forms:

foreach ( $array as $value ) {
    //Do something.
}

foreach( $array as $key => $value ) {
    //Do something.
}

In either structure, $array must be an existing PHP array. The loop will assign each element of that array to $value in turn, and, if $key is specified, that will be assigned the key associated with the $value. An example:

$myFamily['mum'] = "Jane";
$myFamily['dad'] = "James";
$myFamily['grandma'] = "Josephine";
$myFamily['grandad'] = "John";

foreach( $myFamily as $relative => $name ) {
    echo("My $relative's name is $name.<br>");
}

The above code produces the following result:

My mum's name is Jane.
My dad's name is James.
My grandma's name is Josephine.
My grandad's name is John.

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