==> STRINGS--

• , array of character are called strings
•  a string is traditionally a sequence of characters, either as a literal constant or as some kind of variable

==> POINTERS--

• A pointer is a variable which contains the address in memory of another variable.
• Pointers are the variables that are used to store the location of value present in the memory

       Declaration :

                             data_type *variable_name;

                              Ex : int *a;

                  Ex :

                         #include int main()

                         {

                            int var = 20;

                            int *ip;

                            ip=&var;

                            printf(“Address of variable is %x ”, &var);

                            printf(“Address stored in ip variable is :%x”,ip);

                            printf(“value of *ip variable : %d”, *ip);

                            return 0;

                         }  

==> One Dimensional Array---

               Declaration::

                      Syntax: data_type array_name[array_size];

                                   where, data_type can be int, float or char.

                                   array_name is the name of the array.

                                   array_size indicates number of elements in the array.

                                   For ex: int age[5];

             Initialization::

                          Syntax: data_type array_name[array_size]={v1,v2,v3};

                                       where, v1, v2, v3 are the values

                                       For ex: int age[5]={2,4,34,25,18};

==> Two Dimensional Array----

             Declaration::

                            Syntax: data_type array_name[array_size][array_size];

                                          where, first index shows the row number of the element and

                                                         second index shows the coulmn number of the element

            Initialisation::

                             Syntax: data_type array_name[array_size][array_size]={V1,V2,V3,.....Vn};

                                           where, V1, V2, V3,......,Vn are the values

                             For ex: int matrix[2][3]={2,4,56,3,6};

DYNAMIC MEMORY ALLOCATION----

•  It refers to performing manual management for dynamic memory allocation using standard library functions such as malloc, realoc, calloc and free.
• The size of array initially declared can be sometimes insufficient or sometimes more than required but dynamic memory allocation allows a program to obtain more memory space, while running or to release space when not required.

FUNCTIONS OF DYNAMIC MEMORY ALLOCATION----

• There are four standard library functions under “stdlib.h” for dynamic memory allocation. 

1. malloc()
2. calloc()
3. realloc()
4. free()             

=>   malloc() – It allocates requested size of bytes and returns a pointer first byte of allocated space.

                      Syntax : ptr=(data_type *)malloc(bysize);

                      Ex : (int*)malloc(100*sizeof(int)) 

=>   calloc() – Allocates spaces for array elements, initializes to zero and then returns a pointer to memory.

                      Syntax : ptr=(data_type*)calloc(n,element_size);

                      Ex : ptr=(float*)calloc(25,sizeof(float))

=>   realloc() – Changes the size of the previously allocated space according to the requirement.

                      Syntax : ptr=realloc(ptr,newsize);

=>   free() – It deallocates the previously allocated space.

                     Syntax – free(ptr);