Think about the decisions you make before you go to sleep. If you have
something to do the next day, say go to work, school, or an appointment, then
you will set your alarm clock to wake you up. Otherwise, you will sleep in as
long as you like!This simple kind of if/then statement is very common in every day life and also appears in programming quite often. Whenever you want to make a decision given that something is true (you have something to do tomorrow) and be sure that you take the appropriate action, you are using an if/then relationship.
The PHP If Statement
The if statement is necessary for most programming, thus it is important in PHP. Imagine that on January 1st you want to print out "Happy New Year!" at the top of your personal web page. With the use of PHP if statements you could have this process automated, months in advance, occuring every year on January 1st.This idea of planning for future events is something you would never have had the opportunity of doing if you had just stuck with HTML.
Conditional Statements
Very often when you write code, you want to perform different actions for different decisions.You can use conditional statements in your code to do this.
In PHP we have the following conditional statements:
- if statement - use this statement to execute some code only if a specified condition is true
- if...else statement - use this statement to execute some code if a condition is true and another code if the condition is false
- if...elseif....else statement - use this statement to select one of several blocks of code to be executed
- switch statement - use this statement to select one of many blocks of code to be executed
The if Statement
Use the if statement to execute some code only if a specified condition is true.Syntax
if (condition) code to be executed if condition is true;
<html>
<body>
<?php
$d=date("D");
if ($d=="Fri") echo "Have a nice weekend!";
?>
</body>
</html>
<body>
<?php
$d=date("D");
if ($d=="Fri") echo "Have a nice weekend!";
?>
</body>
</html>
The if...else Statement
Use the if....else statement to execute some code if a condition is true and another code if a condition is false.Syntax
if (condition)
{
code to be executed if condition is true;
}
else
{
code to be executed if condition is false;
}
{
code to be executed if condition is true;
}
else
{
code to be executed if condition is false;
}
Example
The following example will output "Have a nice weekend!" if the current day is Friday, otherwise it will output "Have a nice day!":
<html>
<body>
<?php
$d=date("D");
if ($d=="Fri")
{
echo "Have a nice weekend!";
}
else
{
echo "Have a nice day!";
}
?>
</body>
</html>
<body>
<?php
$d=date("D");
if ($d=="Fri")
{
echo "Have a nice weekend!";
}
else
{
echo "Have a nice day!";
}
?>
</body>
</html>
The if...elseif....else Statement.
Use the if....elseif...else statement to select one of several blocks of code to be executed.Syntax
if (condition)
{
code to be executed if condition is true;
}
elseif (condition)
{
code to be executed if condition is true;
}
else
{
code to be executed if condition is false;
}
{
code to be executed if condition is true;
}
elseif (condition)
{
code to be executed if condition is true;
}
else
{
code to be executed if condition is false;
}
Example
The following example will output "Have a nice weekend!" if the current day is Friday, and "Have a nice Sunday!" if the current day is Sunday. Otherwise it will output "Have a nice day!":
<html>
<body>
<?php
$d=date("D");
if ($d=="Fri")
{
echo "Have a nice weekend!";
}
elseif ($d=="Sun")
{
echo "Have a nice Sunday!";
}
else
{
echo "Have a nice day!";
}
?>
</body>
</html>
<body>
<?php
$d=date("D");
if ($d=="Fri")
{
echo "Have a nice weekend!";
}
elseif ($d=="Sun")
{
echo "Have a nice Sunday!";
}
else
{
echo "Have a nice day!";
}
?>
</body>
</html>
A False If Statement
Let us now see what happens when a PHP if statement is not true, in other words, false. Say that we changed the above example to:PHP Code:
$my_name = "anotherguy";
if ( $my_name == "someguy" ) {
echo "Your name is someguy!<br />";
}
echo "Welcome to my homepage!";
Display:
Welcome to my homepage!
Here the variable contained the value "anotherguy", which is not equal to "someguy".
The if statement evaluated to false, so the code segment of the if statement was not
executed. When used properly, the if statement is a powerful tool to have in your
programming arsenal!
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