Explain the purpose of each statement, identify the syntax, and give example codes and the output.

1. SELECTION STRUCTURE
- if statement
- if else statement
- if else if else statement
- switch statement

2. PHP LOOPS
- while statement
- do while statement
- for statement
- for each statement

SELECTION STRUCTURE:

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

Syntax

if (condition) {
    code to be executed if condition is true;
}

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

Example:

<?php
$t = date("H");

if ($t < "20") {
    echo "Have a good day!";
}
?>

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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

if (condition) {
    code to be executed if condition is true;
} else {
    code to be executed if condition is false;}

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

Example:

<?php
$t = date("H");

if ($t < "20") {
    echo "Have a good day!";
} else {
    echo "Have a good night!";
}
?>

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

Syntax

if (condition) {
    code to be executed if this condition is true;} elseif (condition) {
    code to be executed if this condition is true;} else {
    code to be executed if all conditions are false;}

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!"

Example:

<?php
$t = date("H");

if ($t < "10") {
    echo "Have a good morning!";
} elseif ($t < "20") {
    echo "Have a good day!";
} else {
    echo "Have a good night!";
}
?>

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The Switch Statement: The switch statement is used to perform different actions based on different conditions.

Syntax

switch (n) {
    case label1:
        code to be executed if n=label1;
        break;
    case label2:
        code to be executed if n=label2;
        break;
    case label3:
        code to be executed if n=label3;
        break;
    ...
    default:
        code to be executed if n is different from all labels;
}

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.

Example:

<?php
$favcolor = "red";

switch ($favcolor) {
    case "red":
        echo "Your favorite color is red!";
        break;
    case "blue":
        echo "Your favorite color is blue!";
        break;
    case "green":
        echo "Your favorite color is green!";
        break;
    default:
        echo "Your favorite color is neither red, blue, nor green!";
}
?>

---------------------------------------------------------

PHP Loops

While statement: execute a block of code while the specified condition is true.

Syntax

while (condition is true) {
    code to be executed;
}

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++):

Example

<?php 
$x = 1; 

while($x <= 5) {
    echo "The number is: $x <br>";
    $x++;
} 
?>

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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

do {
    code to be executed;} while (condition is true);

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:

Example

<?php 
$x = 1; 

do {
    echo "The number is: $x <br>";
    $x++;
} while ($x <= 5);
?>

---------------------------------------------------------

For statement

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

Syntax

for (init counter; test counter; increment counter) {
    code to be executed;
}

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:

Example:

<?php 
for ($x = 0; $x <= 10; $x++) {
    echo "The number is: $x <br>";
} 
?>

---------------------------------------------------------

For each Statement

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

Syntax

foreach ($array as $value) {
    code to be executed;
}

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):

Example:

<?php 
$colors = array("red", "green", "blue", "yellow"); 

foreach ($colors as $value) {
    echo "$value <br>";
}
?>