In its simpliest form, a conditional executes a block of code if a certain condition exists. If it doesn't exist, the code will be ignored. A variation on that principal is a conditional that executes a block of code if a certain condition exists, and executes a different block of code if the certain condition does not exist.

IF Statement

In plain english, an If statement reads: "If this condition is true, execute this code". The syntax looks like so:

if (condition) { code to be performed }

Here are some examples:

which displays thus:

IF/ELSE Statement

In plain english, an If/else statement reads: "If this condition is true, execute this code, else execute this other code". The syntax looks like so:

if (condition) { code to be performed } else { alternate code to be performed }

Here are some examples:

which displays thus:

IF/ELSEIF/ELSE Statement

In plain english, an If/elseif/else statement reads: "If this condition is true, execute this code, else if this other condition is true, execute this other code, else execute this default code". The syntax looks like so:

if (condition) { code to be performed }
else if (condition) { alternate code to be performed }
else { default code to be performed }

Here is an example:

which displays thus (remember, this server is on UTC):

SWITCH Statement

The Switch statement is an if/elseif/else statement in another form. The Switch statement takes a variable and runs different code depending on the value of the variable.

switch ($variable) {
case "one thing" : // code to do something
  break;
case "something else" : // code to do something else
  break;
case "yet another thing" : // code to do still something else
  break;
default : // default code
}

This is the functional equivalent of:

if ($variable == "one thing") { // code to do something }
else if ($variable == "something else") { // code to do something else }
else if ($variable == "yet another thing") { // code to do still something else }
else { // default code }

The break command tells the computer to stop where it is, forget the rest of the code within the Switch statement and continue after the end of the Switch statement. break ends execution of the current for, foreach, while, do..while or switch structure. More about this when we learn loops.

Here is an example:

which displays thus:

Other Conditional Considerations

For the hard-core programmer, there is a short-cut to the if/else statement called the Ternary Operator. The two statements following are equal:

if (condition) {this;} else {that;} and
(condition) ? this : that;

PHP also has an alternate syntax for conditional statements. When your files are hundreds of lines long and you have complex, nested conditional statements, you sometimes lose your place in the hierarchy of curly braces. In a nutshell, you replace the curly braces with a colon ( : ) and an end statement. Consider the following:

if (condition) : //do some code;
elseif (other condition) : //do some other code;
else : //do default code;
endif;

and

switch (condition) :
case "one thing" : // code to do something
  break;
case "something else" : // code to do something else
  break;
case "yet another thing" : // code to do still something else
  break;
default : // default code
endswitch;

Here are the comparison operators you may use in any conditional: