CONDITIONAL STATEMENTS

What is PHP?

• PHP (recursive acronym for PHP: Hypertext Preprocessor) is a widely-used open source general-purpose scripting language that is especially suited for web development and can be embedded into HTML.
• PHP is probably the most popular scripting language on the web. It is used to enhance web pages.

• With PHP, you can do things like create username and password login pages, check details from a form, create forums, picture galleries, surveys, and a whole lot more.
• If you've come across a web page that ends in PHP, then the author has written some programming code to liven up the plain, old HTML.
• PHP is known as a server-sided language.
• That's because the PHP doesn't get executed on your computer, but on the computer you requested the page from. 

CONTROL STATEMENTS

• PHP supports a number of traditional programming constructs for controlling the flow of execution of a program.
• Conditional statements, such as if/else and switch, allow a program to execute different pieces of code, or none at all, depending on some condition. 
• Loops, such as while and for, support the repeated execution of particular code.

If Statement

The if statement checks the truthfulness of an expression and, if the expression is true, evaluates a statement.

An if statement looks like: Syntax:

if (expression)

  statement

For example:

if ($user_validated)

  echo "Welcome!";

If ... Else Statement

• The If Statement is a way to make decisions based upon the result of a condition. For example, you might have a script that checks if boolean value is true or false, if variable contains number or string value, if an object is empty or populated, etc. 
• The condition can be anything you choose, and you can combine conditions together to make for actions that are more complicated.
• Use the if statement to execute a statement if a logical condition is true. Use the optional else clause to execute a statement if the condition is false. 

The syntax for If statement looks as follows:

if (condition) {    statements_1 } else {    statements_2 } For example: $result = 70; if ($result >= 57) {     echo "Pass "; } else {     echo "Fail "; } ?>  Else ......If Statement if (condition_1) {    statement_1 } [elseif (condition_2) {    statement_2 }] ... [elseif (condition_n_1) {    statement_n_1 }] [else {    statement_n }]

• Next example use the elseif variant on the if statement. This allows us to test for other conditions if the first one wasn't true.
•  The program will test each condition in sequence until:
• It finds one that is true. In this case it executes the code for that condition.
• It reaches an else statement. In which case it executes the code in the else statement.
• It reaches the end of the if ... elseif ... else structure. In this case it moves to the next statement after the conditional structure.

For example:

$result = 70;

if ($result >= 75) {
    echo "Passed: Grade A
";
}
elseif ($result >= 60) {
    echo "Passed: Grade B
";
}
elseif ($result >= 45) {
    echo "Passed: Grade C
";
}
else {
    echo "Failed
";
}
?>

Switch Statement

• Switch statements work the same as if statements. 
• However the difference is that they can check for multiple values. 
• A switch statement allows a program to evaluate an expression and attempt to match the expression's value to a case label. 
• If a match is found, the program executes the associated statement.

 The syntax for the switch statement as follows:

switch (expression) {    case label_1:       statements_1       [break;]    case label_2:       statements_2       [break;]    ...    default:      statements_n      [break;] }

• The program first looks for a case clause with a label matching the value of expression and then transfers control to that clause, executing the associated statements.
• If no matching label is found, the program looks for the optional default clause, and if found, transfers control to that clause, executing the associated statements.
• If no default clause is found, the program continues execution at the statement following the end of switch. 
• Use break to prevent the code from running into the next case automatically.

Let's consider an example:

$flower = "rose"; switch ($flower) {   case "rose" :      echo $flower." costs $2.50";      break;   case "daisy" :      echo $flower." costs $1.25";      break;   case "orchild" :      echo $flower." costs $1.50";      break;   default :      echo "There is no such flower in our shop";      break; } ?> If an expression successfully evaluates to the values specified in more than one case statement, only the first one encountered will be executed.  Once a match is made, PHP stops looking for more matches.