The mysqli extension, or as it is sometimes known, the MySQL improved extension, was developed to take advantage of new features found in MySQL systems versions 4.1.3 and newer. 

The mysqli extension is included with PHP versions 5 and later.  The mysqli extension has a number of benefits, the key enhancements over the mysql extension being:  

=>Object-oriented interface  
=>Support for Prepared Statements  
=>Support for Multiple Statements  
=>Support for Transactions  
=>Enhanced debugging capabilities  
=>Embedded server support

Class: Classes are intended to represent those real-life items that coder like to manipulate within an application.
object: An instance of class is called object.Once the object is created, all characteristic and behaviours define within the class are made available to the newly instantiated object.

PHP does not support multiple inheritances. PHP generally supports single type of inheritance.

Ans: Constant is a value that cannot be modified throughout the execution of a program.Constant are declared by using define () function.

Ans: The difference of print and printf are as the print statement is used output data passed to it, but the printf statement is used t output a blend of statement and dynamic information stored within one or several variable.