Loops

Kama lugha yoyote ile ya programu, uwezo wa kurudia misimbo mara fulani ni muhimu sana. Hapo sasa ndipo mahali loops hutumika, na PHP inatupea taratibu 4 za ku loop. Sura hii itazipitia taratibu hizo zote ikizielezea jinsi zinafanya kazi na mfano.

loop ya while

While Loop labda ndio rahisi kwa zote. Kirahisi inairudia kitalu cha misimbo mradi kauli iliyomo ndani inatathmini kuwa kweli. Mfano waweza kuwa kama hii:

<?php
$i = 0;
while($i < 5)
{
    echo $i."<br>";
    $i++;
}
?>

Jaribu kuikimbiza kipande hiki cha misimbo. Itahesabu hadi 4, sababu tunaendelea hadi $i inawacha kuwa chini ya 5. Kila wakati hiyo loop inajirudia, tunaongeza 1 kwa thamani ya hesabu, $i, na pia tunapo toa thamani ya sasa. Kile utakachoamua kuweka katikati ya kifungo ya while loop, inapaswa iweze kutathmini iwe thamani ya boolean, k.v, Kweli au uongo

The do-while loop

This one works almost exactly like the while loop, with one important difference: With the while loop, the statement is checked before the loop is entered - with the do-while loop, it's checked at the end of an iteration. This means that with the do-while loop, you are guaranteed at least one iteration - with a regular while loop, the code within it may never be reached, if the statement is never evaluated to true. Here is an example showing just this behavior:

<?php
$i = 0;
do
{
    echo $i."<br>";
    $i++;
} while($i < 0);
?>

With a regular while loop, nothing would ever be printed to the user, because $i is 0, and therefore not less than 0 at any point. However, since this is a do-while loop, we get an iteration for free. Afterwards, PHP realizes that the statement does not evaluate to true, and exits the loop.

The for loop

One of the most common loops in PHP, which you might recognize from other programming languages, is the for loop. It will look a bit more complicated than the while loop, but with a bit of practice you may get to like it better. Here is an example using the for loop:

<?php
for($i = 0; $i < 5; $i++)
{
    echo $i."<br />";
}
?>

This will produce the exact same output as the previous while loop, but as you can see, we do it with fewer lines of code. The counter variable is both initialized, tested and incremented with the same line: First we declare it and assign a value to it, then we write the statement to evaluate, and then we increase (or decrease, which is of course possible as well) the variable. Each part is separated with a semicolon. The for loop is nice and compact and good for all situations where you wish to keep track of the amount of iterations.

The foreach loop

The foreach loop in PHP is for iterating through an array. Actually, it only works on arrays, and PHP will issue an error if you try to use it on an unitialized variable, or a variable which doesn't contain an array. The foreach loop comes in two different flavors - here is an example of the first one. Oh, and since arrays haven't been introduced yet, think of them as a list of items for now. In a later chapter, we will look into arrays and how to use them.

<?php
$animals = array("Dog", "Cat", "Snake", "Tiger");

foreach($animals as $animal)
    echo $animal . "<br />";
?>

The nice thing about the foreach loop is that it's designed to work only with arrays, which in turn makes the whole process easier. In each iteration, $animal is assigned the value of the current place in the array, giving us easy access to it. This little snippet of code will simply output a list of the items (in this case animals) in the array.

In this version of the foreach loop, we only get access to the value of the loop. However, each item in an array consists of a key and a value. In our example, we let PHP assign the keys automatically by not explicitly setting them. This is explained in details in the chapter about arrays. In case you need to access the key of the current item in the iteration as well, use the secondary foreach construct, like this:

<?php
$animals = array(1 => "Dog", "Cat", "Snake",    "Tiger");

foreach($animals as $key => $value)
    echo "Animal number " . $key . " is a " . $value . "<br />";
?>

Rahisi namna hiyo.