Lesson 6: Conditions

Conditions are used to execute part of a script only if some predefined requirements (conditions) are fulfilled. For example, a condition could be that a date must be after January 1, 2012 or that a variable is greater than 7.

If...

The first type of condition we will look at is documentationif, which has the following syntax:


	if (condition) {
	   statement
	}

Again, the syntax is very close to ordinary English: If a condition is met, then execute something. Let's look at a simple example:


	<html>

	<head>
	<title>Loops </title>
	</head>
	<body>

	<?php

	$x = 2;

	if ($x > 1) {
	   echo "<p>variable $x is greater than 1 </p>";
	}
	 
	?>

	</body>
	</html>

if ... else ...

The next type of condition will want to look at is documentationelse , which may be presented in the following form:

	
	if (condition) {
	   statement
	}
	else {
	   statement
	}

Again, the syntax is very close to ordinary English: if a condition is met execute something or else execute something else.

In lesson 4, you learned how to find the number of a month. In the following example, we will use the month number in an documentationif documentationelse condition to find out what season it is:


	<html>
	<head>
	<title>Conditions</title>
	</head>
	<body>

	<?php

	if (date ("m") == 3) {
	   echo "<p>Now it's spring!</p> ";
	}
	else {
	   echo "<p>I do not know what season it is!</p> ";	
	}

	?>

	</body>
	</html>
- Show example

As you can see, this condition is not a particularly smart condition - it only works when it's March!

However, there are plenty of ways to improve the condition and make it more precise. Below are listed comparison operators that can be used in the condition:

== Equals
< Less than
> Greater than
<= Less than or equal to
>= Greater than or equal to
!= Not equal to

In addition, there are some logical operators:

&& And
|| Or
! Not

The operators can be used to develop more precise conditions, so now we can expand the above example to include all the spring months:


	<html>
	<head>
	<title>Conditions</title>

	</head>
	<body>

	<?php
 
	if (date("m") >= 3 && date("m") <= 5) {
	   echo "<p> Now it's spring!</p> ";
	}
	else {
	   echo "<p> Now it's either winter, summer or autumn!</p> ";
	}
	 
	?>

	</body>
	</html>

Let's take a closer look at the extended condition:

	date("m") >= 3 && date("m") <= 5

The condition can be translated into:


	If the month is greater than or equal to 3,
	and the month is less than or equal to 5

Smart, eh? Operators play a significant role in many different parts of PHP.

But it still only works with March, April and May. All other months are not yet covered by the condition. So let's try to develop the condition a little more.

if ... elseif ... else...

Using documentationelseif, we can expand the condition and make it work for all months:


	<html>
	<head>
	<title>Conditions</title>

	</head>
	<body>

	<?php
 
	if (date("m") >= 3 && date("m") <= 5) {
	   echo "<p>Now it's spring!</p>";
	}

	elseif (date("m") >= 6 && date("m") <= 8) {
	   echo "<p>Now it's summer!</p>";
	}

	elseif (date("m") >= 9 && date("m") <= 11) {
	   echo "<p>Now it's autumn!</p>";
	}

	else {
	   echo "<p>Now is winter!</p>";
	}
	 
	?>

	</body>
	</html>
- Show example

To write conditions is all about thinking logically and being methodical. The example above is pretty straightforward, but conditions can get very complex.

switch ... case

Another way of writing conditions is to use the documentationswitch method:


	switch (expression) {
 
	case 1: 
	   statement
	   break;	
	case 2: 
	   statement
	   break; 
	default:
	   statement
	   break;
	}

This method is based on an expression and then lists different "answers" or "values" with related statements. The easiest way to explain the method is to show an example.

As you may remember from lesson 4, the function documentationdate("w") returns the current weekday. This can be used in an example where we write the name of the day (instead of a number):


	<html>
	<head>
	<title>Conditions</title>
	</head>
	<body>

	<?php
 
	switch(date("w")) {
	 
	case 1:
	   echo "Now it's Monday";
	   break;
	case 2:
	   echo "Now it's Tuesday";
	   break;
	case 3:
	   echo "Now it's Wednesday";
	   break;
	case 4:
	   echo "Now it's Thursday";
	   break;
	case 5:
	   echo "Now it's Friday";
	   break;
	case 6:
	   echo "Now it's Saturday";
	   break;
	default:
	   echo "Now it's Sunday";
	   break;
	 
	}
	 
	?>

	</body>
	</html>
- Show example

Often documentationswitch can be a good alternative to documentationif documentationelse conditions. What you should use in a given situation depends on which method you find easiest and most logical. Making your scripts logical and clear can be a great challenge.

In the next lesson, we will look at how you can add comments to your scripts to explain how they work. Good comments can be crucial if you or somebody else has to make changes in your codes at a later stage.
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