pre decrement struct single pointer
====================================

In this section, you are going to learn

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		How to iterate structure array using --ptr ?

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                What is the meaning of ``--ptr``, ``*--ptr``, ``*(--ptr)``, ``*--(ptr)``, ``--(*ptr)``, ``--*ptr`` ?

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                What is the meaning of ``c = --ptr``, ``c = *--ptr``, ``c = *(--ptr)``, ``c = *--(ptr)``, ``c = --(*ptr)``, ``c = --*ptr`` ?

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                What is the difference between ``--ptr``, ``*--ptr``, ``*(--ptr)``, ``*--(ptr)``, ``--(*ptr)``, ``--*ptr`` ?

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                What is the difference between ``c = --ptr``, ``c = *--ptr``, ``c = *(--ptr)``, ``c = *--(ptr)``, ``c = --(*ptr)``, ``c = --*ptr`` ?


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		Topics of Pre Decrement

		* :ref:`Basics of Pre Decrement <post_decr_struct_sp_mt_1>`
		* :ref:`Meaning of expressions <post_decr_struct_sp_mt_2>`
		* :ref:`Summary of expressions <post_decr_struct_sp_mt_3>`
		* :ref:`Pre Decrement : struct pointer inside structure <post_decr_struct_sp_mt_4>`
		* :ref:`Pre Decrement : Function Call <post_decr_struct_sp_mt_5>`

.. _post_decr_struct_sp_mt_1:

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		Basics of Pre Decrement

		* :ref:`--ptr Basic Usage <post_decr_struct_sp_ex_1>`
		* :ref:`--ptr : Iterate and print structures of an structure array <post_decr_struct_sp_ex_2>`

.. _post_decr_struct_sp_ex_1:

.. tab-set::

        .. tab-item:: Example 1 : ``--ptr`` : Basic Usage

		* Step 1 : Define a Single dimension array

		.. code-block:: c

			struct User_Data {
				int a;
				int b;
			};

			struct User_Data arr[3] = {
				{ .a = 0, .b = 1 },
				{ .a = 2, .b = 3 },
				{ .a = 4, .b = 5 },
			};

		* Step 2 : Point ``ptr`` to Single dimension array

		.. code-block:: c

		        struct User_Data *ptr;

		        ptr = arr + sizeof(arr)/sizeof(arr[0]) - 1;

		* Step 3 : Decrement ``ptr``

		.. code-block:: c

		        --ptr;

		* Step 4 : Print ``*ptr``

		.. code-block:: c

		        printf("ptr->a = %d\n", ptr->a);
		        printf("ptr->b = %d\n", ptr->b);

		* See full program below

		.. code-block:: c

			#include <stdio.h>

			struct User_Data {
				int a;
				int b;
			};

			int main(void)
			{
				struct User_Data arr[3] = {
					{ .a = 0, .b = 1 },
					{ .a = 2, .b = 3 },
					{ .a = 4, .b = 5 },
				};

			        struct User_Data *ptr;

			        ptr = arr + sizeof(arr)/sizeof(arr[0]) - 1;

			        --ptr;

		        	printf("ptr->a = %d\n", ptr->a);
			        printf("ptr->b = %d\n", ptr->b);

			        return 0;
			}

		* Output is as below

		.. code-block:: c

			ptr->a = 2
			ptr->b = 3

.. _post_decr_struct_sp_ex_2:

.. tab-set::

        .. tab-item:: Example 2 : ``--ptr`` : Iterate and print structures of an structure array

		* Step 1 : Define a Single Dimension array

		.. code-block:: c

			struct User_Data {
				int a;
				int b;
			};

			struct User_Data arr[3] = {
				{ .a = 0, .b = 1 },
				{ .a = 2, .b = 3 },
				{ .a = 4, .b = 5 },
			};

		* Step 2 : Point ``ptr`` to Single dimension array

		.. code-block:: c

		        struct User_Data *ptr;

			ptr = arr + sizeof(arr)/sizeof(arr[0]) - 1;

		* Step 3 : Print structure array by iterating through all structures using ``--ptr``

		.. code-block:: c

		        for (int i = 0; i < 3; i++)
		        {
        			printf("ptr->a = %d\n", ptr->a);
			        printf("ptr->b = %d\n", ptr->b);
		                --ptr;
		        }

		* See full program below

		.. code-block:: c

			#include <stdio.h>

			struct User_Data {
				int a;
				int b;
			};

			int main(void)
			{
				struct User_Data arr[3] = {
					{ .a = 0, .b = 1 },
					{ .a = 2, .b = 3 },
					{ .a = 4, .b = 5 },
				};

			        struct User_Data *ptr;

				ptr = arr + sizeof(arr)/sizeof(arr[0]) - 1;

			        for (int i = 0; i < 3; i++)
			        {   
        				printf("ptr->a = %d\n", ptr->a);
				        printf("ptr->b = %d\n", ptr->b);
			                --ptr;
			        }

			        return 0;
			}

		* Output is as below

		.. code-block:: c

			ptr->a = 4
			ptr->b = 5
			ptr->a = 2
			ptr->b = 3
			ptr->a = 0
			ptr->b = 1

.. _post_decr_struct_sp_mt_2:


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		Meaning of expressions

		* :ref:`Meaning of --ptr and c = --ptr <post_decr_struct_sp_ex_6>`
		* :ref:`Meaning of *(--ptr) and c = *(--ptr) <post_decr_struct_sp_ex_7>`
		* :ref:`Meaning of *--ptr and c = *--ptr <post_decr_struct_sp_ex_10>`
		* :ref:`Meaning of *--(ptr) and c = *--(ptr) <post_decr_struct_sp_ex_8>`
		* :ref:`Meaning of --(*ptr) and c = --(*ptr) <post_decr_struct_sp_ex_9>`


.. _post_decr_struct_sp_ex_6:

.. tab-set::

        .. tab-item:: Meaning of ``--ptr`` and ``c = --ptr``

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			* Consider statement 

			.. code-block:: c

				p = --ptr;

			* There are two steps in this statement

				* ``ptr`` is decremented

				* Current value of ``ptr`` is assigned to ``p``

			* We now derived a rule

				* First Decrement, then Assign

		* Step 1 : Define a single dimension array

		.. code-block:: c

			struct User_Data {
				int a;
				int b;
			};

			struct User_Data arr[3] = {
				{ .a = 0, .b = 1 },
				{ .a = 2, .b = 3 },
				{ .a = 4, .b = 5 },
			};

		* Step 2 : Define a single pointer and point to array

		.. code-block:: c

			struct User_Data *ptr;

			ptr = arr + sizeof(arr)/sizeof(arr[0]);

		OR

		.. code-block:: c

			struct User_Data *ptr;

			ptr = &arr[0] + sizeof(arr)/sizeof(arr[0]);

		* Step 3 : Iterate and print the structure array

		.. code-block:: c

		        for (int i = 0; i < 3; i++)
			{
				struct User_Data *p; 

				p = --ptr;

                		printf("p->a = %d\n", p->a);
		                printf("p->b = %d\n", p->b);
			}

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			Can you guess what is happening ?

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			* Let us Recall 

			.. code-block:: c

				p = --ptr;

			* There are two steps in this statement

				* ``ptr`` is decremented

				* Current value of ``ptr`` is assigned to ``p``

			* We now derived a rule

				* First Decrement, then Assign

		* See full program below

		.. code-block:: c

			#include <stdio.h>

			struct User_Data {
				int a;
				int b;
			};

			int main(void)
			{
				struct User_Data arr[3] = {
					{ .a = 0, .b = 1 },
					{ .a = 2, .b = 3 },
					{ .a = 4, .b = 5 },
				};

			        struct User_Data *ptr;

			        ptr = arr + sizeof(arr)/sizeof(arr[0]);

		        	for (int i = 0; i < 3; i++)
				{
					struct User_Data *p; 

					p = --ptr;

                			printf("p->a = %d\n", p->a);
		                	printf("p->b = %d\n", p->b);
				}

			        return 0;
			}

		* Output is as below

		.. code-block:: c

			p->a = 4
			p->b = 5
			p->a = 2
			p->b = 3
			p->a = 0
			p->b = 1

.. _post_decr_struct_sp_ex_7:

.. tab-set::

        .. tab-item:: Meaning of ``*(--ptr)`` and ``c = *(--ptr)``

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			* Consider statement 

			.. code-block:: c

				c = *(--ptr);

			* There are two steps in this statement

				* ``ptr`` is decremented

				* Current value of ``*ptr`` is assigned to ``c``

				* ``*ptr`` is NOT decremented

			* We now derived a rule

				* First Decrement, then Assign

		* Step 1 : Define a single dimension array

		.. code-block:: c

			struct User_Data {
				int a;
				int b;
			};

			struct User_Data arr[3] = {
				{ .a = 0, .b = 1 },
				{ .a = 2, .b = 3 },
				{ .a = 4, .b = 5 },
			};

		* Step 2 : Define a single pointer and point to array

		.. code-block:: c

			struct User_Data *ptr;

			ptr = arr + sizeof(arr)/sizeof(arr[0]);

		OR

		.. code-block:: c

			struct User_Data *ptr;

			ptr = &arr[0] + sizeof(arr)/sizeof(arr[0]);

		* Step 3 : Iterate and print the structure array

		.. code-block:: c

		        for (int i = 0; i < 3; i++)
			{
				struct User_Data c;

				c = *(--ptr);

				printf("c.a = %d\n", c.a);
				printf("c.b = %d\n", c.b);
			}

		Output is as below

		.. code-block:: c

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			Can you guess what is happening ?


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			* Let us Recall

			.. code-block:: c

				c = *(--ptr);

			* There are two steps in this statement

				* ``ptr`` is decremented

				* Current value of ``*ptr`` is assigned to ``c``

				* ``*ptr`` is NOT decremented

			* We now derived a rule

				* First Decrement, then Assign

		* See full program below

		.. code-block:: c

			#include <stdio.h>

			struct User_Data {
				int a;
				int b;
			};

			int main(void)
			{
				struct User_Data arr[3] = {
					{ .a = 0, .b = 1 },
					{ .a = 2, .b = 3 },
					{ .a = 4, .b = 5 },
				};

			        struct User_Data *ptr;

				ptr = arr + sizeof(arr)/sizeof(arr[0]);

		        	for (int i = 0; i < 3; i++)
				{
					struct User_Data c;

					c = *(--ptr);

					printf("c.a = %d\n", c.a);
					printf("c.b = %d\n", c.b);
				}

			        return 0;
			}

		* Output is as below

		.. code-block:: c

			c.a = 4
			c.b = 5
			c.a = 2
			c.b = 3
			c.a = 0
			c.b = 1

.. _post_decr_struct_sp_ex_10:

.. tab-set::

        .. tab-item:: Meaning of ``*--ptr`` and c = ``*--ptr``

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			* :ref:`Same as *(--ptr) and c = *(--ptr) <post_decr_struct_sp_ex_7>`

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			* Consider statement 

			.. code-block:: c

				c = *--ptr;

			* There are two steps in this statement

				* ``ptr`` is decremented

				* Current value of ``*ptr`` is assigned to ``c``

				* ``*ptr`` is NOT decremented

			* We now derived a rule

				* First Decrement, then Assign

		* Step 1 : Define a single dimension array

		.. code-block:: c

			struct User_Data {
				int a;
				int b;
			};

			struct User_Data arr[3] = {
				{ .a = 0, .b = 1 },
				{ .a = 2, .b = 3 },
				{ .a = 4, .b = 5 },
			};

		* Step 2 : Define a single pointer and point to array

		.. code-block:: c

			struct User_Data *ptr;

			ptr = arr + sizeof(arr)/sizeof(arr[0]);

		OR

		.. code-block:: c

			struct User_Data *ptr;

			ptr = &arr[0] + sizeof(arr)/sizeof(arr[0]);

		* Step 3 : Iterate and print the structure array

		.. code-block:: c

		        for (int i = 0; i < 3; i++)
			{
				struct User_Data c;

				c = *--ptr;

				printf("c.a = %d\n", c.a);
				printf("c.b = %d\n", c.b);
			}

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			Can you guess what is happening ?

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			* Let us Recall

			.. code-block:: c

				c = *--ptr;

			* There are two steps in this statement

				* ``ptr`` is decremented

				* Current value of ``*ptr`` is assigned to ``c``

				* ``*ptr`` is NOT decremented

			* We now derived a rule

				* First Decrement, then Assign

		* See full program below

		.. code-block:: c

			#include <stdio.h>

			struct User_Data {
				int a;
				int b;
			};

			int main(void)
			{
				struct User_Data arr[3] = {
					{ .a = 0, .b = 1 },
					{ .a = 2, .b = 3 },
					{ .a = 4, .b = 5 },
				};

			        struct User_Data *ptr;

				ptr = arr + sizeof(arr)/sizeof(arr[0]);

		        	for (int i = 0; i < 3; i++)
				{
					struct User_Data c;

					c = *--ptr;

					printf("c.a = %d\n", c.a);
					printf("c.b = %d\n", c.b);
				}

			        return 0;
			}

		* Output is as below

		.. code-block:: c

			c.a = 4
			c.b = 5
			c.a = 2
			c.b = 3
			c.a = 0
			c.b = 1

.. _post_decr_struct_sp_ex_8:

.. tab-set::

        .. tab-item:: Meaning of ``*--(ptr)`` and ``c = *--(ptr)``

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			* :ref:`Same as *(--ptr) and c = *(--ptr) <post_decr_struct_sp_ex_7>`

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			* Consider statement 

			.. code-block:: c

				c = *--(ptr);

			* There are two steps in this statement

				* ``ptr`` is decremented

				* Current value of ``*ptr`` is assigned to ``c``

				* ``*ptr`` is NOT decremented

			* We now derived a rule

				* First Decrement, then Assign

		* Step 1 : Define a single dimension array

		.. code-block:: c

			struct User_Data {
				int a;
				int b;
			};

			struct User_Data arr[3] = {
				{ .a = 0, .b = 1 },
				{ .a = 2, .b = 3 },
				{ .a = 4, .b = 5 },
			};

		* Step 2 : Define a single pointer and point to array

		.. code-block:: c

			struct User_Data *ptr;

			ptr = arr + sizeof(arr)/sizeof(arr[0]);

		OR

		.. code-block:: c

			struct User_Data *ptr;

			ptr = &arr[0] + sizeof(arr)/sizeof(arr[0]);

		* Step 3 : Iterate and print the structure array

		.. code-block:: c

		        for (int i = 0; i < 3; i++)
			{
				struct User_Data c;

				c = *--(ptr);

				printf("c.a = %d\n", c.a);
				printf("c.b = %d\n", c.b);
			}

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			Can you guess what is happening ?

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			* Let us Recall

			.. code-block:: c

				c = *--(ptr);

			* There are two steps in this statement

				* ``ptr`` is decremented

				* Current value of ``*ptr`` is assigned to ``c``

				* ``*ptr`` is NOT decremented

			* We now derived a rule

				* First Decrement, then Assign

		* See full program below

		.. code-block:: c

			#include <stdio.h>

			struct User_Data {
				int a;
				int b;
			};

			int main(void)
			{
				struct User_Data arr[3] = {
					{ .a = 0, .b = 1 },
					{ .a = 2, .b = 3 },
					{ .a = 4, .b = 5 },
				};

			        struct User_Data *ptr;

				ptr = arr + sizeof(arr)/sizeof(arr[0]);

		        	for (int i = 0; i < 3; i++)
				{
					struct User_Data c;

					c = *--(ptr);

					printf("c.a = %d\n", c.a);
					printf("c.b = %d\n", c.b);
				}

			        return 0;
			}

		* Output is as below

		.. code-block:: c

			c.a = 4
			c.b = 5
			c.a = 2
			c.b = 3
			c.a = 0
			c.b = 1

.. _post_decr_struct_sp_ex_9:

.. tab-set::

        .. tab-item:: Meaning of ``--(*ptr)`` and ``c = --(*ptr)``

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			* Consider statement 

			.. code-block:: c

				c = --(*ptr);

			* This is invalid usage for a structure pointer !


.. _post_decr_struct_sp_mt_3:


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		Summary of expressions

		* :ref:`Summary of Pre Decrement expressions <post_decr_struct_sp_ex_summary>`


.. _post_decr_struct_sp_ex_summary: 


.. tab-set::

        .. tab-item:: Summary of Pre Decrement expressions

		===================================== =========================================================================
		Expression                            Explanation
		===================================== =========================================================================
                c = --ptr                             * Decrement ``ptr``
                                                      * Assign ``ptr`` to ``c``
                c = \*--ptr                           * Decrement ``ptr``
                                                      * Assign ``*ptr`` to ``c``
                                                      * DO NOT decrement ``*ptr``
                c = \*(--ptr)                         * Decrement ``ptr``
                                                      * Assign ``*ptr`` to ``c``
                                                      * DO NOT decrement ``*ptr``
                c = \*--(ptr)                         * Decrement ``ptr``
                                                      * Assign ``*ptr`` to ``c``
                                                      * DO NOT decrement ``*ptr``
                c = --\*ptr                           * INVALID for structure pointer
                c = --\*(ptr)                         * INVALID for structure pointer
		===================================== =========================================================================


.. _post_decr_struct_sp_mt_4:

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		Pre Decrement : struct pointer inside structure

		* :ref:`Structure pointer accessed using Structure Object <post_decr_struct_sp_ex_struct_ex_1>`
		* :ref:`Structure pointer accessed using Structure Single Pointer <post_decr_struct_sp_ex_struct_ex_2>`
		* :ref:`Structure pointer accessed using Structure Double Pointer <post_decr_struct_sp_ex_struct_ex_3>`
		* :ref:`Structure pointer accessed using Structure Triple Pointer <post_decr_struct_sp_ex_struct_ex_4>`
		* :ref:`Structure pointer accessed using Nested Structure Object <post_decr_struct_sp_ex_struct_ex_5>`
		* :ref:`Structure pointer accessed using Nested Structure Single Pointer <post_decr_struct_sp_ex_struct_ex_6>`
		* :ref:`Structure pointer accessed using Nested Structure 2 level Pointers <post_decr_struct_sp_ex_struct_ex_7>`


.. _post_decr_struct_sp_ex_struct_ex_1:

.. tab-set::

        .. tab-item:: Structure pointer accessed using Structure Object

		* Step 1 : Define a single dimension array

		.. code-block:: c

			struct User_Data {
				int a;
				int b;
			};

			struct User_Data arr[3] = {
				{ .a = 0, .b = 1 },
				{ .a = 2, .b = 3 },
				{ .a = 4, .b = 5 },
			};

		* Step 2 : Create a structure object

		.. code-block:: c

			struct ABC
			{
			        struct User_Data *ptr;
			};

			struct ABC abc;

		* Step 3 : Point single structure pointer to single dimension array

		.. code-block:: c

			abc.ptr = arr + sizeof(arr)/sizeof(arr[0]);

		* Step 4 : Iterate through single dimension array using pointer

		.. code-block:: c

		        for (int i = 0; i < 3; i++)
		        {   
		                struct User_Data c;

		                c = *--abc.ptr;

		                printf("c.a = %d\n", c.a);
		                printf("c.b = %d\n", c.b);
       			}

		* See full program below

		.. code-block:: c

			#include <stdio.h>

			struct User_Data {
				int a;
				int b;
			};

			struct ABC
			{
			        struct User_Data *ptr;
			};

			int main(void)
			{
				struct User_Data arr[3] = {
					{ .a = 0, .b = 1 },
					{ .a = 2, .b = 3 },
					{ .a = 4, .b = 5 },
				};

				struct ABC abc;

				abc.ptr = arr + sizeof(arr)/sizeof(arr[0]);

		        	for (int i = 0; i < 3; i++)
			        {   
			                struct User_Data c;

			                c = *--abc.ptr;

		        	        printf("c.a = %d\n", c.a);
		                	printf("c.b = %d\n", c.b);
	       			}

			        return 0;
			}

		* Output is as below

		.. code-block:: c

			c.a = 4
			c.b = 5
			c.a = 2
			c.b = 3
			c.a = 0
			c.b = 1

.. _post_decr_struct_sp_ex_struct_ex_2:

.. tab-set::

        .. tab-item:: Structure pointer accessed using Structure Single Pointer

		* Step 1 : Define a single dimension array

		.. code-block:: c

			struct User_Data {
				int a;
				int b;
			};

			struct User_Data arr[3] = {
				{ .a = 0, .b = 1 },
				{ .a = 2, .b = 3 },
				{ .a = 4, .b = 5 },
			};

		* Step 2 : Allocate memory for structure pointers

		.. code-block:: c

			struct ABC 
			{
			        struct User_Data *ptr;
			};

			struct ABC *sp;

			sp = malloc(sizeof(struct ABC));

		* Step 3 : Point single structure pointer to single dimension array

		.. code-block:: c

			sp->ptr = arr + sizeof(arr)/sizeof(arr[0]);

		* Step 4 : Iterate through single dimension array using pointer

		.. code-block:: c

		        for (int i = 0; i < 3; i++)
		        {
		                struct User_Data c;

		                c = *--sp->ptr;

		                printf("c.a = %d\n", c.a);
		                printf("c.b = %d\n", c.b); 
		        }

		* Step 5 : Free memory after use

		.. code-block:: c

		        free(sp);

		* See full program below

		.. code-block:: c

			#include <stdio.h>
			#include <stdlib.h>

			struct User_Data {
				int a;
				int b;
			};

			struct ABC 
			{
			        struct User_Data *ptr;
			};

			int main(void)
			{
				struct User_Data arr[3] = {
					{ .a = 0, .b = 1 },
					{ .a = 2, .b = 3 },
					{ .a = 4, .b = 5 },
				};

			        struct ABC *sp;

			        sp = malloc(sizeof(struct ABC));

				sp->ptr = arr + sizeof(arr)/sizeof(arr[0]);

		        	for (int i = 0; i < 3; i++)
			        {
			                struct User_Data c;

			                c = *--sp->ptr;

		        	        printf("c.a = %d\n", c.a);
		                	printf("c.b = %d\n", c.b); 
			        }

			        free(sp);

			        return 0;
			}

		* Output is as below

		.. code-block:: c

			c.a = 4
			c.b = 5
			c.a = 2
			c.b = 3
			c.a = 0
			c.b = 1

.. _post_decr_struct_sp_ex_struct_ex_3:

.. tab-set::

        .. tab-item:: Structure pointer accessed using Structure Double Pointer

		* Step 1 : Define a single dimension array

		.. code-block:: c

			struct User_Data {
				int a;
				int b;
			};

			struct User_Data arr[3] = {
				{ .a = 0, .b = 1 },
				{ .a = 2, .b = 3 },
				{ .a = 4, .b = 5 },
			};

		* Step 2 : Allocate memory for structure pointers

		.. code-block:: c

			struct ABC 
			{
			        struct User_Data *ptr;
			};

		        struct ABC **dp;

		        dp = malloc(sizeof(struct ABC *));
		        *dp = malloc(sizeof(struct ABC )); 

		* Step 3 : Point single structure pointer to single dimension array

		.. code-block:: c

		        (*dp)->ptr = arr + sizeof(arr)/sizeof(arr[0]);

		* Step 4 : Iterate through single dimension array using pointer

		.. code-block:: c

		        for (int i = 0; i < 3; i++)
		        {
		                struct User_Data c;

		                c = *--(*dp)->ptr;

		                printf("c.a = %d\n", c.a);
		                printf("c.b = %d\n", c.b); 
		        }

		* Step 5 : Free memory after use

		.. code-block:: c

		        free(*dp);
		        free(dp);

		* See full program below

		.. code-block:: c

			#include <stdio.h>
			#include <stdlib.h>

			struct User_Data {
				int a;
				int b;
			};

			struct ABC 
			{
			        struct User_Data *ptr;
			};

			int main(void)
			{
				struct User_Data arr[3] = {
					{ .a = 0, .b = 1 },
					{ .a = 2, .b = 3 },
					{ .a = 4, .b = 5 },
				};

			        struct ABC **dp;

			        dp = malloc(sizeof(struct ABC *));
			        *dp = malloc(sizeof(struct ABC )); 

		        	(*dp)->ptr = arr + sizeof(arr)/sizeof(arr[0]);

		        	for (int i = 0; i < 3; i++)
			        {
			                struct User_Data c;

			                c = *--(*dp)->ptr;

		        	        printf("c.a = %d\n", c.a);
		                	printf("c.b = %d\n", c.b); 
			        }

			        free(*dp);
			        free(dp);

			        return 0;
			}

		* Output is as below

		.. code-block:: c

			c.a = 4
			c.b = 5
			c.a = 2
			c.b = 3
			c.a = 0
			c.b = 1

.. _post_decr_struct_sp_ex_struct_ex_4:

.. tab-set::

        .. tab-item:: Structure pointer accessed using Structure Triple Pointer


		* Step 1 : Define a single dimension array

		.. code-block:: c

			struct User_Data {
				int a;
				int b;
			};

			struct User_Data arr[3] = {
				{ .a = 0, .b = 1 },
				{ .a = 2, .b = 3 },
				{ .a = 4, .b = 5 },
			};

		* Step 2 : Allocate memory for structure pointers

		.. code-block:: c

			struct ABC
			{
			        struct User_Data *ptr;
			};

		        struct ABC ***dp;

		        dp = malloc(sizeof(struct ABC **));
		        *dp = malloc(sizeof(struct ABC *));
		        **dp = malloc(sizeof(struct ABC )); 

		* Step 3 : Point single structure pointer to single dimension array

		.. code-block:: c

		        (**dp)->ptr = arr + sizeof(arr)/sizeof(arr[0]);

		* Step 4 : Iterate through single dimension array using pointer

		.. code-block:: c

		        for (int i = 0; i < 3; i++)
		        {
		                struct User_Data c;

		                c = *--(**dp)->ptr;

		                printf("c.a = %d\n", c.a);
		                printf("c.b = %d\n", c.b);
		        }

		* Step 5 : Free memory after use

		.. code-block:: c

		        free(**dp);
		        free(*dp);
		        free(dp);

		* See full program below

		.. code-block:: c

			#include <stdio.h>
			#include <stdlib.h>

			struct User_Data {
				int a;
				int b;
			};

			struct ABC
			{
			        struct User_Data *ptr;
			};

			int main(void)
			{
				struct User_Data arr[3] = {
					{ .a = 0, .b = 1 },
					{ .a = 2, .b = 3 },
					{ .a = 4, .b = 5 },
				};

			        struct ABC ***dp;

			        dp = malloc(sizeof(struct ABC **));
			        *dp = malloc(sizeof(struct ABC *));
			        **dp = malloc(sizeof(struct ABC )); 

		        	(**dp)->ptr = arr + sizeof(arr)/sizeof(arr[0]);

		        	for (int i = 0; i < 3; i++)
			        {
			                struct User_Data c;

			                c = *--(**dp)->ptr;

		        	        printf("c.a = %d\n", c.a);
		                	printf("c.b = %d\n", c.b);
			        }

			        free(**dp);
			        free(*dp);
			        free(dp);

			        return 0;
			}

		* Output is as below

		.. code-block:: c

			c.a = 4
			c.b = 5
			c.a = 2
			c.b = 3
			c.a = 0
			c.b = 1

.. _post_decr_struct_sp_ex_struct_ex_5:

.. tab-set::

        .. tab-item:: Structure pointer accessed using Nested Structure Object


		* Step 1 : Define a single dimension array

		.. code-block:: c

			struct User_Data {
				int a;
				int b;
			};

			struct User_Data arr[3] = {
				{ .a = 0, .b = 1 },
				{ .a = 2, .b = 3 },
				{ .a = 4, .b = 5 },
			};

		* Step 2 : Create a structure object

		.. code-block:: c

			struct PQR
			{
			        struct User_Data *ptr;
			};

			struct ABC 
			{
			        struct PQR pqr;
			};

		        struct ABC abc;

		* Step 3 : Point single structure pointer to single dimension array

		.. code-block:: c

			abc.pqr.ptr = arr + sizeof(arr)/sizeof(arr[0]);

		* Step 4 : Iterate through single dimension array using pointer

		.. code-block:: c

		        for (int i = 0; i < 3; i++)
		        {
		                struct User_Data c;

		                c = *--abc.pqr.ptr;

		                printf("c.a = %d\n", c.a);
		                printf("c.b = %d\n", c.b);
		        }

		* See full program below

		.. code-block:: c

			#include <stdio.h>

			struct User_Data {
				int a;
				int b;
			};

			struct PQR
			{
			        struct User_Data *ptr;
			};

			struct ABC 
			{
			        struct PQR pqr;
			};

			int main(void)
			{
				struct User_Data arr[3] = {
					{ .a = 0, .b = 1 },
					{ .a = 2, .b = 3 },
					{ .a = 4, .b = 5 },
				};

			        struct ABC abc;

				abc.pqr.ptr = arr + sizeof(arr)/sizeof(arr[0]);

		        	for (int i = 0; i < 3; i++)
			        {
			                struct User_Data c;

			                c = *--abc.pqr.ptr;

		        	        printf("c.a = %d\n", c.a);
		                	printf("c.b = %d\n", c.b);
			        }

			        return 0;
			}

		* Output is as below

		.. code-block:: c

			c.a = 4
			c.b = 5
			c.a = 2
			c.b = 3
			c.a = 0
			c.b = 1

.. _post_decr_struct_sp_ex_struct_ex_6:

.. tab-set::

        .. tab-item:: Structure pointer accessed using Nested Structure Single Pointer

		* Step 1 : Define a single dimension array

		.. code-block:: c

			struct User_Data {
				int a;
				int b;
			};

			struct User_Data arr[3] = {
				{ .a = 0, .b = 1 },
				{ .a = 2, .b = 3 },
				{ .a = 4, .b = 5 },
			};

		* Step 2 : Allocate memory for structure pointers

		.. code-block:: c

			struct PQR 
			{
			        struct User_Data *ptr;
			};

			struct ABC 
			{
			        struct PQR pqr;
			};

		        struct ABC *sp;

		        sp = malloc(sizeof(struct ABC));

		* Step 3 : Point single structure pointer to single dimension array

		.. code-block:: c

		        sp->pqr.ptr = arr + sizeof(arr)/sizeof(arr[0]);

		* Step 4 : Iterate through single dimension array using pointer

		.. code-block:: c

		        for (int i = 0; i < 3; i++)
		        {
		                struct User_Data c;

		                c = *--sp->pqr.ptr;

		                printf("c.a = %d\n", c.a);
		                printf("c.b = %d\n", c.b); 
		        }

		* Step 5 : Free memory after use

		.. code-block:: c

		        free(sp);

		* See full program below

		.. code-block:: c

			#include <stdio.h>
			#include <stdlib.h>

			struct User_Data {
				int a;
				int b;
			};

			struct PQR 
			{
			        struct User_Data *ptr;
			};

			struct ABC 
			{
			        struct PQR pqr;
			};

			int main(void)
			{
				struct User_Data arr[3] = {
					{ .a = 0, .b = 1 },
					{ .a = 2, .b = 3 },
					{ .a = 4, .b = 5 },
				};

			        struct ABC *sp;

			        sp = malloc(sizeof(struct ABC));

			        sp->pqr.ptr = arr + sizeof(arr)/sizeof(arr[0]);

		        	for (int i = 0; i < 3; i++)
			        {
			                struct User_Data c;

			                c = *--sp->pqr.ptr;

		        	        printf("c.a = %d\n", c.a);
		                	printf("c.b = %d\n", c.b); 
			        }

			        free(sp);

			        return 0;
			}

		* Output is as below

		.. code-block:: c

			c.a = 4
			c.b = 5
			c.a = 2
			c.b = 3
			c.a = 0
			c.b = 1

.. _post_decr_struct_sp_ex_struct_ex_7:

.. tab-set::

        .. tab-item:: Structure pointer accessed using Nested Structure 2 level Pointers 

		* Step 1 : Define a single dimension array

		.. code-block:: c

			struct User_Data {
				int a;
				int b;
			};

			struct User_Data arr[3] = {
				{ .a = 0, .b = 1 },
				{ .a = 2, .b = 3 },
				{ .a = 4, .b = 5 },
			};

		* Step 2 : Allocate memory for structure pointers

		.. code-block:: c

			struct PQR
			{
			        struct User_Data *ptr;
			};

			struct ABC
			{
			        struct PQR *pqr;
			};

		        struct ABC *abc;

		        abc = malloc(sizeof(struct ABC));
		        abc->pqr = malloc(sizeof(struct PQR));

		* Step 3 : Point single structure pointer to single dimension array

		.. code-block:: c

		        abc->pqr->ptr = arr + sizeof(arr)/sizeof(arr[0]);

		* Step 4 : Iterate through single dimension array using pointer

		.. code-block:: c

		        for (int i = 0; i < 3; i++)
		        {
		                struct User_Data c;

		                c = *--abc->pqr->ptr;

		                printf("c.a = %d\n", c.a);
		                printf("c.b = %d\n", c.b);
        		}

		* Step 5 : Free memory after use

		.. code-block:: c

		        free(abc->pqr);
		        free(abc);

		* See full program below

		.. code-block:: c

			#include <stdio.h>
			#include <stdlib.h>

			struct User_Data {
				int a;
				int b;
			};

			struct PQR
			{
			        struct User_Data *ptr;
			};

			struct ABC
			{
			        struct PQR *pqr;
			};

			int main(void)
			{
				struct User_Data arr[3] = {
					{ .a = 0, .b = 1 },
					{ .a = 2, .b = 3 },
					{ .a = 4, .b = 5 },
				};

			        struct ABC *abc;

			        abc = malloc(sizeof(struct ABC));
			        abc->pqr = malloc(sizeof(struct PQR));

			        abc->pqr->ptr = arr + sizeof(arr)/sizeof(arr[0]);

		        	for (int i = 0; i < 3; i++)
			        {
			                struct User_Data c;

			                c = *--abc->pqr->ptr;

		        	        printf("c.a = %d\n", c.a);
		                	printf("c.b = %d\n", c.b);
	        		}

			        free(abc->pqr);
			        free(abc);

			        return 0;
			}

		* Output is as below

		.. code-block:: c

			c.a = 4
			c.b = 5
			c.a = 2
			c.b = 3
			c.a = 0
			c.b = 1

.. _post_decr_struct_sp_mt_5:


	.. panels::
		:container: container pb-4
		:column: col-lg-12 p-2
		:card: shadow

		Pre Decrement : Function Call

		* :ref:`*--ptr : Function Call <post_decr_struct_sp_call_by_value_ex_1>`
		* :ref:`--ptr : Function Call <post_decr_struct_sp_call_by_value_ex_2>`


.. _post_decr_struct_sp_call_by_value_ex_1:

.. tab-set::

        .. tab-item:: \*--ptr : Function Call

		* Step 1 : Define a single dimension array

		.. code-block:: c

			struct User_Data {
				int a;
				int b;
			};

			struct User_Data arr[3] = {
				{ .a = 0, .b = 1 },
				{ .a = 2, .b = 3 },
				{ .a = 4, .b = 5 },
			};

		* Step 2 : Define a single pointer and point to array

		.. code-block:: c

			struct User_Data *ptr;

			ptr = arr + sizeof(arr)/sizeof(arr[0]);

		* Step 3 : Iterate array using --ptr and Pass by Value

		.. code-block:: c

		        for (int i = 0; i < 3; i++)
			{
				fun(*--ptr);
			}

		* Step 4 : Define a function ``fun`` which receives a structure from caller

		.. code-block:: c

			void fun(struct User_Data c)
			{
				printf("c.a = %d\n", c.a);
				printf("c.b = %d\n", c.b);
			}

		.. panels::
			:container: container pb-4
			:column: col-lg-12 p-2
			:card: shadow

			Let us Recall,

			* In case of ``*--ptr``

				* ``ptr`` is decremented first, then current value of ``*ptr`` is assigned
			
			* Hence, in this case

				* ``ptr`` is decremented first, then current value of ``*ptr`` is passed as arguement to function ``fun``

		* See full program below

		.. code-block:: c

			#include <stdio.h>

			struct User_Data {
				int a;
				int b;
			};

			void fun(struct User_Data c)
			{
				printf("c.a = %d\n", c.a);
				printf("c.b = %d\n", c.b);
			}

			int main(void)
			{
				struct User_Data arr[3] = {
					{ .a = 0, .b = 1 },
					{ .a = 2, .b = 3 },
					{ .a = 4, .b = 5 },
				};

			        struct User_Data *ptr;

				ptr = arr + sizeof(arr)/sizeof(arr[0]);

		        	for (int i = 0; i < 3; i++)
			        {
			                fun(*--ptr);
			        }

			        return 0;
			}

		* Output is as below

		.. code-block:: c

			c.a = 4
			c.b = 5
			c.a = 2
			c.b = 3
			c.a = 0
			c.b = 1

.. _post_decr_struct_sp_call_by_value_ex_2:

.. tab-set::

        .. tab-item:: --ptr : Function Call

		* Step 1 : Define a single dimension array

		.. code-block:: c

			struct User_Data {
				int a;
				int b;
			};

			struct User_Data arr[3] = {
				{ .a = 0, .b = 1 },
				{ .a = 2, .b = 3 },
				{ .a = 4, .b = 5 },
			};

		* Step 2 : Define a single pointer and point to array

		.. code-block:: c

			struct User_Data *ptr;

			ptr = arr + sizeof(arr)/sizeof(arr[0]);

		* Step 3 : Iterate array using --ptr and Pass by Value

		.. code-block:: c

		        for (int i = 0; i < 3; i++)
			{
				fun(--ptr);
			}

		* Step 4 : Define a function ``fun`` which receives a structure pointer from caller

		.. code-block:: c

			void fun(struct User_Data *c)
			{
				printf("c->a = %d\n", c->a);
				printf("c->b = %d\n", c->b);
			}

		.. panels::
			:container: container pb-4
			:column: col-lg-12 p-2
			:card: shadow

			Let us Recall,

			* In case of ``--ptr``

				* `ptr`` is first decremented, then assigned
			
			* Hence, in this case

				* `ptr`` is first decremented, then current value of ``ptr`` is assigned as argument to function ``fun``

		* See full program below

		.. code-block:: c

			#include <stdio.h>

			struct User_Data {
				int a;
				int b;
			};

			void fun(struct User_Data *c)
			{
				printf("c->a = %d\n", c->a);
				printf("c->b = %d\n", c->b);
			}

			int main(void)
			{
				struct User_Data arr[3] = {
					{ .a = 0, .b = 1 },
					{ .a = 2, .b = 3 },
					{ .a = 4, .b = 5 },
				};

			        struct User_Data *ptr;

				ptr = arr + sizeof(arr)/sizeof(arr[0]);

		        	for (int i = 0; i < 3; i++)
			        {
			                fun(--ptr);
			        }

			        return 0;
			}

		* Output is as below

		.. code-block:: c

			c->a = 4
			c->b = 5
			c->a = 2
			c->b = 3
			c->a = 0
			c->b = 1

.. card:: See Also

        * Current Module

                * :doc:`../pre_decr_ptr`

        * Previous Module

                * :doc:`../../post_incr_ptr/post_incr_ptr`

        * Next Module

                * :doc:`../../post_decr_ptr/post_decr_ptr`

        * Other Modules

                * :doc:`../../variable_and_ptr/variable_and_ptr`
                * :doc:`../../array_n_ptrs/array_n_ptrs`
                * :doc:`../../malloc_ptr/malloc_ptr`
                * :doc:`../../typecasting_n_ptr/typecasting_n_ptr`
                * :doc:`../../funcs_n_ptrs/funcs_n_ptrs`
                * :doc:`../../memcpy_ptr/memcpy_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:`../../pre_incr_ptr/pre_incr_ptr`