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Using Control Structures in PHP


If you are a beginner to PHP, learning how to use control structures is a must. In this article Joel will assist you guys by providing coherent examples.

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By: Joel Philip
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April 26, 2003

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If you are a beginner to PHP, learning how to use control structures is a must. In this article Joel will assist you guys by providing coherent examples.

Control structures are beneficial when coding in PHP. Many tasks can be accomplished with a small amount of coding but basic understanding on how to use them will solve many coding problems.

What are Control Structures?

Control Structures are often referred to as Conditionals, Branching or their familiar name, "Loops".

Loops are great for retrieving information from databases, constructing tables and building dynamic pulldown menus.

Here is a list of the different types of conditionals in PHP:

  • if/else
  • if/elseif/else
  • do/while
  • for
  • while
  • foreach

The "if/else" conditional is the most commonly used statement in PHP coding.

View the following code:

<?php
$number ='5';
if($number =='3')
{
echo "The number is equal to 3";
}
else
{
echo "The number is equal to $number";
}
?>

Explanation of the code:

  1. The $number variable sets it's value to 5.
  2. If the $number variable is equal to 3 and becomes true the echo language construct displays the number is equal to 3. This statement is FALSE.
  3. Since the $number variable is really a value of 5 then it continues until it reaches the end of the conditional and displays The number is equal to 5. This statement is TRUE.

Extending the conditional with the "if/elseif/else" statement would allow more options.

View the following code:

<?php
$number = 7;
if($number == '5')
{
echo "The number is not equal to 7";
}
elseif($number <> '9')
{

echo "The number is not equal to 9";
}
else
{
echo "The number is equal to $number";
}
?>

Explanation of the code:

  1. The $number variable sets it's value to 7.
  2. If the $number variable is equal to 5, the echo language construct displays that its not equal to 7. This statement is FALSE.
  3. If the $number variable is not equal to 9, the echo language construct displays it is not equal to 9. This statement is TRUE.
  4. The second conditional is the true statement of the script and the script terminates.

Lets turn to "Loops" starting with the "for" conditional. The basic structure will continue looping until it resolves to FALSE.

Here is an example of the "for" conditional that builds a pulldown menu with the years specified by the variable $x and the operand on the right.

View the following code:

<?php
echo '<FORM ACTION="results.php" METHOD=post>';
echo '<SELECT name=year>';
echo"<OPTION VALUE=\"/\">Pick a year</OPTION>";
for($x = 1950; $x <= 2003; $x++)
{
echo "<OPTION VALUE=$x>$x</OPTION>";
}
echo "</SELECT></FORM>";
?>

Explanation of the code:

  1. A pulldown form is created complete with method and action.
  2. The variable, $year is specified but the values are not set.
  3. The top position on the pulldown menu is created using a forward slash to equal null and displays the "Pick a year" portion of the menu.
  4. The "for" loop counts from the first value, 1950 and loops until it reaches the value or year, 2003.
  5. The curly brace helps exit the loop and the closing tags finish the form.

The "while" conditional helps loop through the tables of a database to retrieve the information and display onto a page.

Here is an example of the "while" conditional creating a dynamic pulldown menu from a database:

<?php
include('config.php');
dbconnect();
$sql = SELECT DISTINCT(column_name) FROM $table_name;
$result = @mysql_query($sql);
echo "<FORM method=POST action=results.php>";
echo "<SELECT NAME=column_name>";
while($row = @mysql_fetch_array($result))
{
echo "<OPTION VALUE=\"$row[0]\">$row[0]</OPTION>";
}
echo "<INPUT TYPE=submit name=submit VALUE=\"Get Results\"></SELECT></FORM>";
?>

Explanation of the code:

  1. An include file holds functions and database related information used by the script. The script connects to the database and selects the table.
  2. The query selects the distinct column and narrows it down to the specified rows of the table.
  3. The query values are set and the form is created using the column name derived from the SQL commands.
  4. The "while" loop creates the pulldown menu and the row values are set.

Creating a pulldown menu that contains the months of the year would be bothersome using HTML. Using an array to hold the information and the "foreach()" statement helps speed things up in the long run.

View the following code:

<?php
$month = array("January", "February", "March", "April", "May", "June", "July", "August", "September", "October", "Novemeber", "December");
echo "<FORM METHOD=POST ACTION = results.php>";
echo "<SELECT NAME=column_name >";
echo"<OPTION VALUE=\"/\">Pick a Month</OPTION>";
foreach($month as $MON)
{
echo "<OPTION VALUE=\"$MON\">$MON</OPTION>";
}
echo "</SELECT></FORM>";
?>

Explanation of the code:

  1. An array is created with the names of all 12 months.
  2. The form is constructed with the method and action.
  3. The top position on the pulldown menu, labeled "Pick a Month" is created using a forward slash and it's value is set to null.
  4. The foreach construct extracts the values of the $month variable and produces the pulldown menu with each month's name.
  5. The curly brace helps exit the loop and the closing tags finish the form.

I hope this gives you an understanding of Control Structures and how to use conditionals to your advantage.

Happy coding and remember, "Let the code do the work".

Copyright 2003 - Written by Joel Philip - http://www.phpcollege.com


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