Chapter 9: Pointers and String

Pointer: Definition A pointer is a variable which contains the address in memory of another variable. Through pointers a developer can directly access memory from his/her code which makes memory related operations very fast. But, with great power comes great responsibility.

Why Pointers Pointers make the programs simple and reduce their length. Pointers are helpful in allocation and de-allocation of memory during the execution of the program. Thus, pointers are the instruments of dynamic memory management. Pointers enhance the execution speed of a program. Pointers are helpful in traversing through arrays and character strings. Storage of strings through pointers saves memory space. Pointers may be used to pass on arrays, strings, functions, and variables as arguments of a function. Passing on arrays by pointers saves lot of memory because we are passing on only the address of array instead of all the elements of an array, which would mean passing on copies of all the elements and thus taking lot of memory space. Pointers are used to construct different data structures such as linked lists, queues, stacks, etc.

Declaring Pointer Variable Styntax: datatype *pointer name; Example: int *ptr; char *p;

The address and indirection operator Address Operator: & is address operator. Assigns address to pointer variable Eg: int x =10 , *ptr; ptr=&x; Indirection operator * is indirection operator Eg: int x =10 , *ptr, y; y=*ptr;

Example 1

Pointers as Argument We can pass pointer as argument. As address is directly passed, this can change the variable value. Calling function should pass address Called function should accept address in pointer Eg: swap(&x,&y); ………………. void swap (int *p, int *q) { ………………….}

Example 2

Example 3: Finding Largest and smallest Element in array

Pointer as return value Can be used to return value

Pointer arithmetic C supports only three forms of pointer arithmetic Adding an integer to pointer Subtracting an integer from pointer Subtracting one pointer from another

Passing array as Pointer in function Example 5 and lecture

String Literals String literal is sequence of characters enclosed within double quotes. “ hara hara Mahadeva”

Escape Sequence in String Literals “ Candy\nIs dandy\But liquor\nIs quicker Result Candy Is dandy But liquor Is quicker

How Strings Literals are stored Stored as character of array with null character C use \0 as escape sequence to store numm character.

String Variables Use array with datatype char Initializing a string variable Eg: char x[]=“ILOVEYOU”

Reading and writing strings printf() or puts() function are used %s is conversion specifier Example 7: char str[]=“Let there be peace”; printf(“%s\n”, str); printf(“%.4s”,str);

Reading String scanf or gets Use conversion specifier %s with printf()

Some string Manipulating Function strcmp() strrev() strupr() strlwr() And many more

Some examples Write C code for following problem by using and not using standard library function Check whether two string are same or not using Copy one string to another Count vowel and consonant in string Display different pattern using loop Delete all vowel in string Change to lower case and uppercase