Functions and Integer
============================

In this section, you are going to learn

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	What are the basic properties of a integer ?

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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:`Integer : Syntax <funcs_n_ptrs_int_ex_0_0>`

		* :ref:`Integer : FAQs <funcs_n_ptrs_int_ex_0_1>`

		* :ref:`Integer : Basic Properties <funcs_n_ptrs_int_ex_1>`

		* :ref:`Integer : Call by Value <funcs_n_ptrs_int_ex_2>`

		* :ref:`Integer : Call by Reference <funcs_n_ptrs_int_ex_3>`

		* :ref:`Summary <funcs_n_ptrs_int_ex_4>`

.. _funcs_n_ptrs_int_ex_0_0:

.. tab-set::

        .. tab-item:: Integer : Syntax

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			int c;

.. _funcs_n_ptrs_int_ex_0_1:

.. tab-set::

        .. tab-item:: Integer : FAQs

                Consider a Integer

                .. code-block:: c

                        int c;

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                        Let us answer few basic questions about a Integer


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

                        .. dropdown:: See Answer

                                Number of Integers = 1

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                        How many bytes are there in this Integer ?

                        .. dropdown:: See Answer

                                Number of Bytes = 4

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                        What is the sizeof the Integer ?

                        .. dropdown:: See Answer

                                sizeof(a) = Number of Bytes = 4

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                        How many bits are there in this Integer ?

                        .. dropdown:: See Answer

                                Number of bits = sizeof(c) * 8 = 4 * 8 = 32 bits


.. _funcs_n_ptrs_int_ex_1:

.. tab-set::

        .. tab-item:: Integer : Basic Properties

		Consider a integer

		.. code-block:: c

			int c;

		Then below are the properties of a integer

		=================== ========================================
		Expression	    ?
		=================== ========================================
		c		    ``c`` is a integer
		&c		    ``&c`` is address of integer ``c``
		\*c                 NOT VALID
		sizeof(c)           4 Bytes
		sizeof(&c)          8 Bytes
	        typeof(c)           ``int``
		typeof(&c)          ``int *``
		=================== ========================================

.. _funcs_n_ptrs_int_ex_2:

.. tab-set::

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

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			Integer passed to a function

		* Step 1 : Define a integer

		.. code-block:: c

			int c = 5;

		* Step 2 : Pass integer to a function

		.. code-block:: c

			fun(c);

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

		.. code-block:: c

			void fun(int c)
			{

			}

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

		.. code-block:: c

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

		* See full program below

		.. code-block:: c

			#include <stdio.h>

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

			int main(void)
			{
			        int 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_int_ex_3:

.. tab-set::

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

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			Address of Integer passed to a function

		* Step 1 : Define a integer

		.. code-block:: c

			int c = 5;

		* Step 2 : Pass address of integer to a function

		.. code-block:: c

			fun(&c);

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

		.. code-block:: c

			void fun(int *p)
			{

			}

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

		.. code-block:: c

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

		* See full program below

		.. code-block:: c

			#include <stdio.h>

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

			int main(void)
			{
			        int 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_int_ex_4:

.. tab-set::

        .. tab-item:: Summary

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

.. card:: See Also

	* Other topics of integer and functions

                * :doc:`./int`
                * :doc:`./int_sd_array`
                * :doc:`./int_dd_array`
                * :doc:`./int_td_array`
                * :doc:`./int_sp`
                * :doc:`./int_dp`
                * :doc:`./int_tp`

        * Current Module

                * :doc:`../funcs_n_ptrs`

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                * :doc:`../../typecasting_n_ptr/typecasting_n_ptr`

        * Next Module

                * :doc:`../../memcpy_ptr/memcpy_ptr`

        * 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`