1. Chapter 9: Pointers and String

2. 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.

3. 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.

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

5. 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;

6. Example 1

7. 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) { ………………….}

8. Example 2

9. Example 3: Finding Largest and smallest Element in array

10. Pointer as return value
Can be used to return value

11. 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

12. Passing array as Pointer in function
Example 5 and lecture

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

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

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

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

17. 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);

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

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

20. 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