Ring/Lessons/Variables

Variables

To create a new variable, you just need to determine the variable name & value. The value will determine the variable type and you can change the value to switch between the types using the same variable name.

Syntax:

<Variable Name> = <Value>

.. tip::

The operator '=' is used here as an Assignment operator and the same operator can be used in conditions, but for testing equality of expressions.

.. note::

The Variable will contains the real value (not a reference). This means that once you change the variable value, the old value will be removed from memory (even if the variable contains a list or object).

Dynamic Typing

Ring is a dynamic programming language that uses `Dynamic Typing <http://en.wikipedia.org/wiki/Type_system>`_.

x = "Hello"		# x is a string
see x + nl
x = 5			# x is a number (int)
see x + nl
x = 1.2 		# x is a number (double)
see x + nl
x = [1,2,3,4]		# x is a list
see x 			# print list items
x = date()		# x is a string contains date
see x + nl
x = time()		# x is a string contains time
see x + nl
x = true		# x is a number (logical value = 1)
see x + nl
x = false		# x is a number (logical value = 0)
see x + nl

Deep Copy

We can use the assignment operator '=' to copy variables. We can do that to copy values like strings & numbers. Also, we can copy complete lists & objects. The assignment operator will do a complete duplication for us. This operation called `Deep Copy <http://en.wikipedia.org/wiki/Object_copy#Deep_copy>`_

list = [1,2,3,"four","five"]
list2 = list
list = []
See list	# print the first list - no items to print
See "********" + nl
See list2	# print the second list - contains 5 items

Weakly Typed

Ring is a `weakly typed language <http://en.wikipedia.org/wiki/Strong_and_weak_typing>`_, this means that the language can automatically convert between data types (like string & numbers) when that conversion make sense.

Rules:

<NUMBER> + <STRING> --> <NUMBER>
<STRING> + <NUMBER> --> <STRING>

.. note::

The same operator '+' can be used as an arithmetic operator or for string concatenation.

Example:

x = 10			# x is a number
y = "20"		# y is a string
sum = x + y		# sum is a number (y will be converted to a number)
Msg = "Sum = " + sum 	# Msg is a string (sum will be converted to a string)
see Msg + nl