Learn PHP Tutorial in Hindi Part 2

This video is made for learning about Constants and Variables in PHP.


Constants and Variables

What are Constants?
A constant is an entity whose value does not change throughout the program execution.
For example:
define ("SITE", "abc.com");

What are Variables?
• A variable is a special container that you can define, which then “holds” a value.
• A variable is an entity whose value keeps on changing throughout the program execution. However, it's not a rule that the value of the variable will change.
• However the main difference between variable and constant is that we can't change the value of constant in between the program, but we can change the value of the variable during program execution.
For example:
$num = 7;
PHP is loosely typed, meaning that it automatically determines the data type at the time data is assigned to each variable.

Variable Naming Rules:
• Variable names can contain only the characters: a-z, A-Z, 0-9, and _ (underscore).
• Variable names may not contain spaces.
• Variable names are case-sensitive.

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

In PHP we have the following conditional statements:

if statement - executes some code only if a specified condition is true
if...else statement - executes some code if a condition is true and another code if the condition is false
if...elseif....else statement - specifies a new condition to test, if the first condition is false
switch statement - selects one of many blocks of code to be executed

There may be several elseifs within the same if statement. The first elseif expression (if any) that evaluates to TRUE would be executed. In PHP, you can also write 'else if' (in two words) and the behavior would be identical to the one of 'elseif' (in a single word). The syntactic meaning is slightly different (if you're familiar with C, this is the same behavior) but the bottom line is that both would result in exactly the same behavior.

The elseif statement is only executed if the preceding if expression and any preceding elseif expressions evaluated to FALSE, and the current elseif expression evaluated to TRUE.

The switch statement is similar to a series of IF statements on the same expression. In many occasions, you may want to compare the same variable (or expression) with many different values, and execute a different piece of code depending on which value it equals to. This is exactly what the switch statement is for.

t is important to understand how the switch statement is executed in order to avoid mistakes. The switch statement executes line by line (actually, statement by statement). In the beginning, no code is executed. Only when a case statement is found with a value that matches the value of the switch expression does PHP begin to execute the statements. PHP continues to execute the statements until the end of the switch block, or the first time it sees a break statement. If you don't write a break statement at the end of a case's statement list, PHP will go on executing the statements of the following case.

The case expression may be any expression that evaluates to a simple type, that is, integer or floating-point numbers and strings. Arrays or objects cannot be used here unless they are dereferenced to a simple type.

You may have noticed the lack of a place for code when the variable doesn't match our condition. The if statement has the else clause and the switch statement has the default case.

It's usually a good idea to always include the default case in all your switch statements. Below is a variation of our example that will result in none of the cases being used causing our switch statement to fall back and use the default case.

Ternary operator logic is the process of using "(condition) ? (true return value) : (false return value)" statements to shorten your if/else structures.

What Are The Advantages of Ternary Logic?
There are some valuable advantages to using this type of logic:

Makes coding simple if/else logic quicker
You can do your if/else logic inline with output instead of breaking your output building for if/else statements
Makes code shorter
Makes maintaining code quicker, easier