Question-11. What are the rules for determine the “truth” of any value not already of the Boolean type ?
Answer- Here are the rules for determine the “truth” of any value not already of the Boolean type −
• If the value is a number, it is false if exactly equal to zero and true otherwise. • If the value is a string, it is false if the string is empty (has zero characters) or is the string "0", and is true otherwise. • Values of type NULL are always false. • If the value is an array, it is false if it contains no other values, and it is true otherwise. For an object, containing a value means having a member variable that has been assigned a value. • Valid resources are true (although some functions that return resources when they are successful will return FALSE when unsuccessful). • Don't use double as Booleans.
Question-12. What is NULL ?
Answer- NULL is a special type that only has one value: NULL. To give a variable the NULL value, simply assign it like this −
$my_var = NULL;
The special constant NULL is capitalized by convention, but actually it is case insensitive; you could just as well have typed −
$my_var = null;
A variable that has been assigned NULL has the following properties:
It evaluates to FALSE in a Boolean context. It returns FALSE when tested with IsSet() function.
Question-13. How will you define a constant in PHP ?
Answer- To define a constant you have to use define() function and to retrieve the value of a constant, you have to simply specifying its name. Unlike with variables, you do not need to have a constant with a $.
Question-14. What is the purpose of constant() function ?
Answer- As indicated by the name, this function will return the value of the constant. This is useful when you want to retrieve value of a constant, but you do not know its name, i.e. It is stored in a variable or returned by a function.
define("MINSIZE", 50);
echo MINSIZE;
echo constant("MINSIZE"); // same thing as the previous line
Only scalar data (boolean, integer, float and string) can be contained in constants.
Question-15. What are the differences between PHP constants and variables ?
Answer-
• There is no need to write a dollar sign ($) before a constant, where as in Variable one has to write a dollar sign. • Constants cannot be defined by simple assignment, they may only be defined using the define() function. • Constants may be defined and accessed anywhere without regard to variable scoping rules. • Once the Constants have been set, may not be redefined or undefined.
Question-16. What are PHP magic constants ?
Answer- PHP provides a large number of predefined constants to any script which it runs known as magic constants.
Question-17. What is the purpose of _LINE_ constant ?
Answer- _LINE_ − The current line number of the file.
Question-18. What is the purpose of _FILE_ constant ?
Answer- _FILE_ − The full path and filename of the file. If used inside an include, the name of the included file is returned. Since PHP 4.0.2, _FILE_ always contains an absolute path whereas in older versions it contained relative path under some circumstances.
Question-19. What is the purpose of _FUNCTION_ constant ?
Answer- _FUNCTION_ − The function name. (Added in PHP 4.3.0) As of PHP 5 this constant returns the function name as it was declared (case-sensitive). In PHP 4 its value is always lowercased.
Question-20. What is the purpose of _CLASS_ constant ?
Answer- _CLASS_ − The class name. (Added in PHP 4.3.0) As of PHP 5 this constant returns the class name as it was declared (case-sensitive). In PHP 4 its value is always lowercased.