SubPrograms
Types:
			
(1) Functions
(2) Subroutine
(1) Functions
	In programming, a function is a routine that a value as an input, and produces a single value as an output.
	Types:

	(a) System Defined Functions

		(i) Numeric System Defined Functions
		
		ABS(X)
		ASC(A$)
		CINT(N)
		FIX(N)
		INT(A)
		LOG(N)
		RND(N)
		SIN(A)
		SPC(A)
		SQR(A)
		TAN(N)
		TAB(A)
		VAL(STRING$)
		(ii) String System Defined Functions
	
		CHR$(n)
		DATE$
		HEX$(a)
		MID$(STRING $, n1, n2)
		OCT$(N)
		RIGHT$(STRING $, N)
		LEFT$(STRING $, N)
		SPACE$(A)
		TIME$
	(b) User Defined Functions
		DEF FN name [Argument] expression
(2) Subroutine
	GOSUB
	RETURN

Difference between Functions and Subroutin?
Function:

(a) A Function is pre-defined program.
(b) It is used in an expression to call a predetermined operation on an operand.
Subroutine:
(a) A Subroutine itself is a small program consisting of set of statements which are usually written within a main program.
(b) A Subroutine can be used to calculate and return many values.