📝 variables entry to the guide.

doc/src/guide.rst

@@ -102,5 +102,71 @@ tuples, with the addition of concatenation (``+``) and duplication (``*``) opera
     [3, 6, 8][1] # returns 6
     "love" in ["love", "pizzas"] # returns true
 
+To access an array value, the operator ``[]`` can be used.
+For instance, syntax ``[3]`` means: "give me the third element".
+Arrays can be nested, that's why the operator ``[]`` can take several arguments.
+As an example, let's consider the following syntax ``[1, 2, 3]``
+means: "give me the third element of the second element of the first element of my array".
+
+.. code-block::
+    :caption: array
+
+    [[1, 2], [3, 4]] [0, 1] # equals 2
+    [[1, 2], [3, 4]] [0, 0] # equals 1
+    [[1, 2], [3, 4]] [1, 1] # equals 4
+
+Declaring variables
+-------------------
+Variables declaration is a fundamental feature of pratically all programming languages.
+Some use only mutable variables (like Python), and others allow the programmer
+to declare immutable variables (like C for instance).
+CCM offer two syntaxes for declaring variables:
+the ``var`` keyword is used to declare mutable variables, and the ``const``
+keyword declares immutable one.
+
+Storing expression using variables
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+Variables are containers for storing expressions.
+To declare a variable, we use the keyword ``var``
+followed by the name of the variable as well as its value: ``var name = expr``.
+
+Variables can be reassigned later using the syntax ``name = expr``, and they can be
+used everywhere an expression can be.
+
+.. code-block::
+   :caption: mutable variable declaration
+
+    var x = 37
+    x # equals 37
+    x = 7
+    x # equals 7
 
 
+Immutability using constants
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+A constant is an immutable values storage similaire to classical variables.
+The fundamental difference between constants and variables is mutability:
+variables can be reassigned, constants cannot.
+If you try to change the value of a constant, an error will be raised.
+
+
+.. code-block::
+   :caption: immutable variable declaration
+
+    const x = 37
+    x # equals 37
+    x = 7 # ILLEGAL
+
+Dereferencing arrays
+~~~~~~~~~~~~~~~~~~~~
+Variables can contain any expression, and in particular it could store an array.
+To access array elements, the operator ``[]`` can be used directly after the variable name.
+
+.. code-block::
+   :caption: Array dereferencement
+
+    var x = [2, 4, 6]
+    x[1] # equals 4
+
+I
+