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If Else
=============

Decision making is required when we want to execute a code only if a certain condition is satisfied.

if
--------------------
.. code-block:: python

    if test expression:
        statement(s)

Here, the program evaluates the `test expression` and executes the `statement` only when the `test expression` is True.

If `test expression` is False, then `statement(s)` will not be executed.

In MicroPython, indentation means the body of the `if` statement. The body starts with an indentation and ends with the first unindented line.

Python interprets non-zero values ​​as "True". None and 0 are interpreted as "False".

**if Statement Flowchart**

.. image:: img/if_statement.png

**Example**

.. code-block:: python

    num = 8
    if num > 0:
        print(num, "is a positive number.")
    print("End with this line")

>>> %Run -c $EDITOR_CONTENT
8 is a positive number.
End with this line



if...else
-----------------------

.. code-block:: python

    if test expression:
        Body of if
    else:
        Body of else

The `if..else` statement evaluates `test expression` and will execute the body of `if` only when the test condition is `True`.

If the condition is `False`, the body of `else` is executed. Indentation is used to separate the blocks.

**if...else Statement Flowchart**

.. image:: img/if_else.png

**Example**

.. code-block:: python

    num = -8
    if num > 0:
        print(num, "is a positive number.")
    else:
        print(num, "is a negative number.")

>>> %Run -c $EDITOR_CONTENT
-8 is a negative number.



if...elif...else
--------------------

.. code-block:: python

    if test expression:
        Body of if
    elif test expression:
        Body of elif
    else: 
        Body of else

`Elif` is short for `else if`. It allows us to check multiple expressions.

If the condition of the `if` is False, the condition of the next elif block is checked, and so on.

If all conditions are `False`, the body of `else` is executed.

Only one of several `if...elif...else` blocks is executed according to the conditions.

The `if` block can only have one `else` block. But it can have multiple `elif` blocks.

**if...elif...else Statement Flowchart**

.. image:: img/if_elif_else.png

**Example**

.. code-block:: python

    x = 10
    y = 9

    if x > y:
        print("x is greater than y")
    elif x == y:
        print("x and y are equal")
    else:
        print("x is greater than y")

>>> %Run -c $EDITOR_CONTENT
x is greater than y


Nested if
---------------------

We can embed an if statement into another if statement, and then call it a nested if statement.

**Example**

.. code-block:: python

    x = 67

    if x > 10:
        print("Above ten,")
        if x > 20:
            print("and also above 20!")
        else:
            print("but not above 20.")

>>> %Run -c $EDITOR_CONTENT
Above ten,
and also above 20!