Course Name - PHP

Data Types and Operators

PHP Conditional Statements

Conditional statements are used to perform different actions based on different conditions.

Very often when you write code, you want to perform different actions for different conditions. You can use conditional statements in your code to do this.

In PHP we have the following conditional statements:

• if statement - executes some code if one condition is true
• if...else statement - executes some code if a condition is true and another code if that condition is false
• if...elseif....else statement - executes different codes for more than two conditions
• switch statement - selects one of many blocks of code to be executed

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PHP - The if Statement

The if statement executes some code if one condition is true.

Syntax

The example below will output "Have a good day!" if the current time (HOUR) is less than 20:

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PHP - The if...else Statement

The if....else statement executes some code if a condition is true and another code if that condition is false.

Syntax

The example below will output "Have a good day!" if the current time is less than 20, and "Have a good night!" otherwise:

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PHP - The if...elseif....else Statement

The if....elseif...else statement executes different codes for more than two conditions.

Syntax

The example below will output "Have a good morning!" if the current time is less than 10, and "Have a good day!" if the current time is less than 20. Otherwise it will output "Have a good night!":

The PHP switch Statement

Use the switch statement to select one of many blocks of code to be executed .

Syntax

This is how it works: First we have a single expression n (most often a variable), that is evaluated once. The value of the expression is then compared with the values for each case in the structure. If there is a match, the block of code associated with that case is executed. Use break to prevent the code from running into the next case automatically. The default statement is used if no match is found.

PHP Loops

Often when you write code, you want the same block of code to run over and over again in a row. Instead of adding several almost equal code-lines in a script, we can use loops to perform a task like this.

In PHP, we have the following looping statements:

• while - loops through a block of code as long as the specified condition is true
• do...while - loops through a block of code once, and then repeats the loop as long as the specified condition is true
• for - loops through a block of code a specified number of times
• foreach - loops through a block of code for each element in an array

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The PHP while Loop

The while loop executes a block of code as long as the specified condition is true.

Syntax

The example below first sets a variable $x to 1 ($x = 1). Then, the while loop will continue to run as long as $x is less than, or equal to 5 ($x <= 5). $x will increase by 1 each time the loop runs ($x++):

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The PHP do...while Loop

The do...while loop will always execute the block of code once, it will then check the condition, and repeat the loop while the specified condition is true.

Syntax

The example below first sets a variable $x to 1 ($x = 1). Then, the do while loop will write some output, and then increment the variable $x with 1. Then the condition is checked (is $x less than, or equal to 5?), and the loop will continue to run as long as $x is less than, or equal to 5:

Notice that in a do while loop the condition is tested AFTER executing the statements within the loop. This means that the do while loop would execute its statements at least once, even if the condition is false the first time.

The example below sets the $x variable to 6, then it runs the loop, and then the condition is checked :

The PHP for Loop

The for loop is used when you know in advance how many times the script should run.

PHP for loops execute a block of code a specified number of times.

Syntax

Parameters:

• init counter: Initialize the loop counter value
• test counter: Evaluated for each loop iteration. If it evaluates to TRUE, the loop continues. If it evaluates to FALSE, the loop ends.
• increment counter: Increases the loop counter value

The example below displays the numbers from 0 to 10:

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The PHP foreach Loop

The foreach loop works only on arrays, and is used to loop through each key/value pair in an array.

Syntax

For every loop iteration, the value of the current array element is assigned to $value and the array pointer is moved by one, until it reaches the last array element.

The following example demonstrates a loop that will output the values of the given array ($colors):

PHP Functions

The real power of PHP comes from its functions; it has more than 1000 built-in functions.

Besides the built-in PHP functions, we can create our own functions.

A function is a block of statements that can be used repeatedly in a program.

A function will not execute immediately when a page loads.

A function will be executed by a call to the function.

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Create a User Defined Function in PHP

A user defined function declaration starts with the word "function":

Syntax

Note: A function name can start with a letter or underscore (not a number).

Tip: Give the function a name that reflects what the function does!

In the example below, we create a function named "writeMsg()". The opening curly brace ( { ) indicates the beginning of the function code and the closing curly brace ( } ) indicates the end of the function. The function outputs "Hello world!". To call the function, just write its name:

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PHP Function Arguments

Information can be passed to functions through arguments. An argument is just like a variable.

Arguments are specified after the function name, inside the parentheses. You can add as many arguments as you want, just separate them with a comma.

The following example has a function with one argument ($fname). When the familyName() function is called, we also pass along a name (e.g. Jani), and the name is used inside the function, which outputs several different first names, but an equal last name:

The following example has a function with two arguments ($fname and $year):

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PHP Default Argument Value

The following example shows how to use a default parameter. If we call the function setHeight() without arguments it takes the default value as argument:

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PHP Functions - Returning values

To let a function return a value, use the return statement: 

Dynamic Function Calls

It is possible to assign function names as strings to variables and then treat these variables exactly as you would the function name itself. Following example depicts this behaviour.

<html>
   
   <head>
      <title>Dynamic Function Calls</title>
   </head>
   
   <body>
      
      <?php
         function sayHello() {
            echo "Hello<br />";
         }
         
         $function_holder = "sayHello";
         $function_holder();
      ?>
      
   </body>
</html>

This will display following result −

Hello