Functions and Character
============================

In this section, you are going to learn

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	What are the basic properties of a character ?

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	What is Call by Value ?

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	What is Call by Reference ?

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	Topics in this section,

		* :ref:`Character : Syntax <funcs_n_ptrs_char_ex_0_0>`

		* :ref:`Character : FAQs <funcs_n_ptrs_char_ex_0_1>`

		* :ref:`Character : Basic Properties <funcs_n_ptrs_char_ex_1>`

		* :ref:`Character : Call by Value <funcs_n_ptrs_char_ex_2>`

		* :ref:`Character : Call by Reference <funcs_n_ptrs_char_ex_3>`

		* :ref:`Summary <funcs_n_ptrs_char_ex_4>`

.. _funcs_n_ptrs_char_ex_0_0:

.. tab-set::

        .. tab-item:: Character : Syntax

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			char c;

.. _funcs_n_ptrs_char_ex_0_1:

.. tab-set::

        .. tab-item:: Character : FAQs

                Consider a Character

                .. code-block:: c

                        char c;

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                        Let us answer few basic questions about a Character


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                        How many characters can be stored in ``c`` ?

                        .. dropdown:: See Answer

                                Number of Characters = 1

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                        How many bytes are there in this Character ?

                        .. dropdown:: See Answer

                                Number of Bytes = 1

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                        What is the sizeof the Character ?

                        .. dropdown:: See Answer

                                sizeof(a) = Number of Bytes = 1 

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                        How many bits are there in this Character ?

                        .. dropdown:: See Answer

                                Number of bits = sizeof(c) * 8 = 1 * 8 = 8 bits


.. _funcs_n_ptrs_char_ex_1:

.. tab-set::

        .. tab-item:: Character : Basic Properties

		Consider a character

		.. code-block:: c

			char c;

		Then below are the properties of a character

		=================== ========================================
		Expression	    ?
		=================== ========================================
		c		    ``c`` is a character
		&c		    ``&c`` is address of character ``c``
		\*c                  NOT VALID
		sizeof(c)           1 Byte
		sizeof(&c)          8 Bytes
	        typeof(c)           ``char``
		typeof(&c)          ``char *``
		=================== ========================================

.. _funcs_n_ptrs_char_ex_2:

.. tab-set::

        .. tab-item:: Character : Call by Value

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			Character passed to a function

		* Step 1 : Define a character

		.. code-block:: c

			char c = 5;

		* Step 2 : Pass character to a function

		.. code-block:: c

			fun(c);

		* Step 3 : Define a function ``fun``

		.. code-block:: c

			void fun(char c)
			{

			}

		* Step 4 : Change character inside function ``fun`` 

		.. code-block:: c

			void fun(char c)
			{
				c = 10;
			}

		* See full program below

		.. code-block:: c

			#include <stdio.h>

			void fun(char c)
			{
			        c = 10;
			}

			int main(void)
			{
			        char c = 5;

			        printf("Before : c = %d\n", c);

			        fun(c);

			        printf("After : c = %d\n", c);

			        return 0;
			}

		* See full program below

		.. code-block:: c

			Before : c = 5
			After  : c = 5

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			Can you guess what is happening ?

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			After function ``fun`` is called,

			* There are two stack frames			

			* Stack frame of ``main``
			* Stack frame of ``fun``
			* variable ``c`` is created on stack frame of ``main``
			* variable ``c`` is created on stack frame of ``fun``
			* Even though name of variable ``c`` is same in ``main`` and ``fun``, they are two different variables in memory
			* Hence changing value of ``c`` inside function ``fun`` does not change the value of ``c`` inside ``main``

.. _funcs_n_ptrs_char_ex_3:

.. tab-set::

        .. tab-item:: Character : Call by Reference

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			Address of Character passed to a function

		* Step 1 : Define a character

		.. code-block:: c

			char c = 5;

		* Step 2 : Pass address of character to a function

		.. code-block:: c

			fun(&c);

		* Step 3 : Define a function ``fun``

		.. code-block:: c

			void fun(char *p)
			{

			}

		* Step 4 : Change character inside function ``fun`` 

		.. code-block:: c

			void fun(char *p)
			{
				*p = 10;
			}

		* See full program below

		.. code-block:: c

			#include <stdio.h>

			void fun(char *p)
			{
			        *p = 10;
			}

			int main(void)
			{
			        char c = 5;

			        printf("Before : c = %d\n", c);

			        fun(&c);

			        printf("After : c = %d\n", c);

			        return 0;
			}

		* Output is as below

		.. code-block:: c

			Before : c = 5
			After  : c = 10

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			Can you guess what is happening ?

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			Let us solve it with equations method !

		* Rule 1 : Base Rule

		.. code-block:: c

			p = &c

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			* RHS is actual parameter. In this case ``&c`` is actual parameter

			* LHS is formal parameter. In this case ``p`` is formal parameter

		* Rule 2 : Move ``&`` from RHS to LHS. This becomes ``*`` on LHS

		.. code-block:: c

			*p = c

		* Rule 3 : Changing ``*p`` also changes ``c``. Because we proved ``*p`` is equal to ``c``

.. _funcs_n_ptrs_char_ex_4:

.. tab-set::

        .. tab-item:: Summary

		================================ ========================= ==========================================================================
		Function Call                    Function Definition       Observations
		================================ ========================= ==========================================================================
		fun(c)                           void fun(char c) { }      Changing ``c`` inside ``fun`` DOES NOT change value of ``c`` in caller
		fun(&c)                          void fun(char \*p) { }    Changing ``*p`` inside ``fun`` CHANGES value of ``c`` in caller
		================================ ========================= ==========================================================================

.. card:: See Also

	* Other topics of character and functions

		* :doc:`./char`
		* :doc:`./char_sd_array`
		* :doc:`./char_dd_array`
		* :doc:`./char_td_array`
		* :doc:`./char_sp`
		* :doc:`./char_dp`
		* :doc:`./char_tp`

        * Current Module

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        * Next Module

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        * Other Modules

                * :doc:`../../variable_and_ptr/variable_and_ptr`
                * :doc:`../../array_n_ptrs/array_n_ptrs`
                * :doc:`../../malloc_ptr/malloc_ptr`
                * :doc:`../../const_ptr/const_ptr`
                * :doc:`../../void_ptr/void_ptr`
                * :doc:`../../array_of_ptr/array_of_ptr`
                * :doc:`../../ptr_to_array/ptr_to_array`
                * :doc:`../../function_ptr/function_ptr`
                * :doc:`../../pre_incr_ptr/pre_incr_ptr`
                * :doc:`../../post_incr_ptr/post_incr_ptr`
                * :doc:`../../pre_decr_ptr/pre_decr_ptr`
                * :doc:`../../post_decr_ptr/post_decr_ptr`