PHP How to use decision making

The if, elseif ...else and switch statements are used to take decision based on the different condition.
You can use conditional statements in your code to make your decisions. PHP supports following threedecision making statements:
  • if...else statement - use this statement if you want to execute a set of code when a condition is true and another if the condition is not true
  • elseif statement - is used with the if...else statement to execute a set of code if one of several condition are true
  • switch statement - is used if you want to select one of many blocks of code to be executed, use the Switch statement. The switch statement is used to avoid long blocks of if..elseif..else code.

The If...Else Statement

If you want to execute some code if a condition is true and another code if a condition is false, use the if....else statement.

Syntax

if (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, 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>
If more than one line should be executed if a condition is true/false, the lines should be enclosed within curly braces:
<html>

<body>
<?php
$d=date("D");
if ($d=="Fri")
  {
  echo "Hello!<br />"; 
  echo "Have a nice weekend!";
  echo "See you on Monday!";
  }
?>
</body>
</html>

The ElseIf Statement

If you want to execute some code if one of several conditions are true use the elseif statement

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;

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>

The Switch Statement

If you want to select one of many blocks of code to be executed, use the Switch statement.
The switch statement is used to avoid long blocks of if..elseif..else code.

Syntax

switch (expression)
{
case label1:
  code to be executed if expression = label1;
  break;  
case label2:
  code to be executed if expression = label2;
  break;
default:
  code to be executed
  if expression is different 
  from both label1 and label2;

}

Example

The switch statement works in an unusual way. First it evaluates given expression then seeks a lable to match the resulting value. If a matching value is found then the code associated with the matching label will be executed or if none of the lables match then statement will will execute any specified default code.
<html>
<body>
<?php
$d=date("D");
switch ($d)
{
case "Mon":
  echo "Today is Monday";
  break;
case "Tue":
  echo "Today is Tuesday";
  break;
case "Wed":
  echo "Today is Wednesday";
  break;
case "Thu":
  echo "Today is Thursday";
  break;
case "Fri":
  echo "Today is Friday";
  break;
case "Sat":
  echo "Today is Saturday";
  break;
case "Sun":
  echo "Today is Sunday";
  break;
default:
  echo "Wonder which day is this ?";
}
?>
</body>
</html>

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