Loop Holes

Last updated 24 Sep 2005

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In this tutorial you will learn how to loop through data in an array using PHP. At the end, you will be able to apply this knowledge to outputting data using all 4 types of loops and even output data from a mySQL database.

Introduction:

An array is a data structure that allows you to hold data in a grid structure, similar to your multiplication tables. It is often necessary to loop through this structure and pull out the data. This can be used for creating tables in HTML, making reports or just outputting the results from a mySQL database.

Types of loops:

PHP has 4 types of loops with each behaving differently. The 4 types of loops are: while, do…while, for and foreach.

The While loop:

While loops will continue to loop while a condition is true. For example we might choose to loop through an array of colors until we find our favorite.

Syntax: while(condition)

Example:

<?php // Our list of colors $colors=Array( 'red', 'yellow', 'green', 'blue', 'purple', 'pink'); $favorite_color="blue"; //My favorite Color //Lets print out the colors in the array until we find the one we like. $iCount=0; //Counter to keep track of colors while($colors[$iCount]!=$favorite_color) { //Print out the color echo $colors[$iCount] . ' is not my favorite color. '; $iCount++; //increases the counter by 1 } echo ' ' . $favorite_color . ' is my favorite color! '; ?>

As you can see from the example, we will continue looping through the colors until we get to "blue" my favorite color. Here is what we would see if we ran the code:

red is not my favorite color.
yellow is not my favorite color.
green is not my favorite color.

blue is my favorite color!

The do..while loop:

do..While loops will continue to loop while a condition is met. However, unlike while this loop will always complete at least once, then continue until the conditionis false. For example we might choose to loop through an array of numbers until the total equals a certain max.

Syntax:

do {
code
}
while(condition)

Example:

<?php // Our list of numbers $numbers=Array(0, 1, 4, 2, 4, 5); $max=10; //max total //Lets add the numbers together until we meet or exceed the max in this case 10. $iCount=0; //Counter to keep track of numbers $iSum=0; //Sum of the numbers thus far do { //Print out the total thus far echo $iSum . ' + ' . $numbers[$iCount] . ' = '; $iSum+=$numbers[$iCount]; //Adds the two numbers together. echo $iSum . ' '; //Final total $iCount++; //increases the counter by 1 } while($iSum<=$max); ?>

As you can see from the example, we will continue looping through the numbers until we get to the total of 11 because 11 is greater than our max of 10, so the loop stops.:

0 + 0 = 0
0 + 1 = 1
1 + 4 = 5
5 + 2 = 7
7 + 4 = 11

The for loop:

The for loop is used when you know how many times you want to execute a statement or a list of statements.

Syntax:

for (initialization; condition; increment)
{
code to be executed;
}

Note: The for statement has three parameters. The first parameter is for initializing variables, the second parameter holds the condition, and the third parameter contains any increments required to implement the loop. If more than one variable is included in either the initialization or the increment section, then they should be separated by commas. The condition must evaluate to true or false.

In our example we will loop through the list of numbers again, and add them all together.

<?php // Our list of colors $numbers=Array(0, 1, 4, 2, 4, 5); $num_elements=count($numbers); //Count how many numbers in the array $iSum=0; //Sum of the numbers thus far for($i=0; $i<$num_elements; $i++) //$i=0 is the counter, and it is initialized to 0 //$i<$count is the condition, and it means loop until $i is greater than or equal to $num_elements //$i++ adds 1 to the value of $i on each pass through { //Print out the total thus far echo $iSum . ' + ' . $numbers[$i] . ' = '; $iSum+=$numbers[$i]; //Adds the two numbers together. echo $iSum . ' '; //Final total } ?>

Output:

0 + 0 = 0
0 + 1 = 1
1 + 4 = 5
5 + 2 = 7
7 + 4 = 11
11 + 5 = 16

The foreach loop

This loop automatically loops through an entire array of values. While doing so it will assign the value of the array to the variable named. For example we will loop over an array of names and assign them to the $name variable.

Syntax:

foreach (array as value)
{
code to be executed;
}

Example:

<?php // Our list of names $names=Array('Warrick', 'Extremer', 'Mr_Muffinman', 'Valerie', 'Koug', 'B!'); //start the list echo '<ul>'; foreach($names as $name) { //Print out the names in a list echo "<li>$name</li>"; } //finish the list echo '</ul>'; ?>

Output:

Warrick
Extremer
Mr_Muffinman
Valerie
Koug
B!

Conclusion:

Loops are very handy for outputting data, especially when you use mySQL. For my last example I will show you how to output a user list.

<?php //Lets connect to a mySQl server $conn=mysql_connect('localhost', 'db_username', 'db_password') or die(mysql_error()); mysql_selectdb('users', $conn); //Select the database to use //Lets generate our sql query $sql='select username from users;'; $result=mysql_query($sql, $conn) or die(mysql_error()); $RecordCount = mysql_num_rows($result); //num records //Start the list echo "<ul>"; for($i=0;$i<$RecordCount;$i++) { $data = mysql_fetch_row($result); //get 1 row from the db //Print out the usernames in a list echo "<li>" . $data[0] . "</li>"; } //finish the list echo '</ul>'; ?>

Output:

Warrick
Extremer
Mr_Muffinman
Valerie
Koug
B!

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Loop Holes

Last updated 24 Sep 2005

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