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Concept of Memory Allocation in C Programming

As the stored program concept specifies, the data and instructions that are to be processed should be stored in main memory of the computer, the memory allocation comes into picture. The data that is to be processed must be stored in main memory so that is readily available to the processor and can fetched and stores in internal registers for processing. Reserving space in main memory for the data variables and used for storing data in it later through assignment or input is called as memory allocation. So once the data structure is decided and variables are declared in the declaration part of the program (in case of C language) memory is allocated to the variables of the respective data structured by the compiler. This is called as memory allocation. For example, consider the following C program:-
           void main()
            int a, b, c;
            . . . . .
When the above  program is compiled memory of two bytes each is allocated to the variables a, b and c respectively. These memory locations are used to store two bytes signed integers (data). In the program the data are referred through variables names (identifiers). Consider another example,
         void main()
            int arr[20];
            . . . . .

When this program is compiled 40 bytes of consecutive memory is allocated to store 20 integers and all the integers are referred by a single variable “arr” with the proper index.
         void main()
            int *arr; int size=20;
            arr= (int *) malloc (2 * size);
When the above program is executed 40 bytes of memory is allocated during execution and the base address is stored in a pointer variable arr. With the help of arr now it is possible to refer 20 integers.
           The above mentioned all examples explain basic concept of memory allocation.


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Memory representation of Linked List

             In memory the linked list is stored in scattered cells (locations).The memory for each node is allocated dynamically means as and when required. So the Linked List can increase as per the user wish and the size is not fixed, it can vary.

               Suppose first node of linked list is allocated with an address 1008. Its graphical representation looks like the figure shown below:

      Suppose next node is allocated at an address 506, so the list becomes,

  Suppose next node is allocated with an address with an address 10,s the list become,

The other way to represent the linked list is as shown below:

 In the above representation the data stored in the linked list is “INDIA”, the information part of each node contains one character. The external pointer root points to first node’s address 1005. The link part of the node containing information I contains 1007, the address of next node. The last node …