Chapter covered Binary Search-definition, advantages,disadvantages Functions-Library & user defined functions Pointers

1. C

2. Contents
 Binary Search
 Functions
 Pointers

3. Binary Search
Binary search is a searching algorithm that works
efficiently with a sorted list. The algorithm finds the
position of a particular element in the array. This
algorithm doesn’t work with the unsorted list.
For Example, The analogy of a telephone directory.
When we search for a particular name in the
directory, we first open the dictionary from the
middle and then decide whether to look in the first
part or the second part of the directory. Again, we
open some page in the middle and the whole process is
repeated until we have the name.

4. Advantages
 The binary search is fast as compared to linear
search.
 Time complexity is high in both average and worst
case.
 Most Suitable for sorted arrays.

5. DISADVANTAGES
 The main disadvantage of binary search is that it
only works with an array of sorted array.

6. Functions
Function is a set of self contained block of statements
that performs a specific task of some kind. A function
is small, complete & independent program. The
specified task is repeated each time the program
calls the function. It breaks the large computing tasks
into smaller ones.
In C there are two types of functions:
1. Library Functions
2. User defined functions

7. Library Functions
Library functions are predefined
built-in functions. These functions
are permanently stored in the
library of C compiler. We can’t
change the meaning of these
functions. Such functions are
stored in header file. A header file
has an extension “.h”

8. Header Files Functions Defined
stdio.h Printf(), scanf(), getchar(),
putchar(), gets(), puts(), fopen(),
fclose()
conio.h Clrscr(), getch()
Ctype.h Toupper(), tolower()
Math.h Pow(), sqrt(), cos(), log()
Stdlib.h exit()
String.h Strlen(), strcpy(), strupr()

9. USER DEFINED FUNCTIONS
Defined by user at the time of writing
the program.
There are three aspect of working with
user-defined functions:
1.Function Declaration, also known as
function prototype
2.Function Definition
3.Function use, also known as function
call or function invocation

10. Function Declaration : we declare the prototype and number
of argument required for function.
Syntax :
return_type function_name (argument1,argument2.....)
eg : int div(int , int) { }
1 - int is a return type of function.
2 - div is a name for function.
3 - two int are arguments required to call the function.

11. Function Definition : Function Definition, also known as
function implementation, means composing a function.
Every Function definition consists of two Parts:
 Header of the function,
 Body of the function.
return_type function_name(parameter_list)
{
// Function body
}
Example- int greatest(int a, int b,int c)/*formal arguments*/
{
//Body of the function
}

12. How to access & execute a function
User defined functions are accessed in same way
as of the library functions i.e. we can access the
function by referring its name, including actual
arguments.
Example- int greatest(10,20,30)/* know as dummy
variables*/

13. return Statement : The return statement is used
in a function to transfer the control from the
called function back to the calling function at the
point of reference. We can also return the value
through return statement to the calling function.
Example : return;
or
return(exp);

14. Passing Arguments to a function
We pass data to a function via argument list . These
are enclosed with brackets or parenthesis after
function name.
There are two ways to pass arguments to a
function:
1. Call by value
2. Call by reference

15.  Call by Value:
In this method the values of actual arguments are
passed to the function. When the control is
transferred to the called function the formal
arguments of function are replaced by the actual
arguments & then the body of function is
executed.
 Call by reference:
In this the address of the actual arguments are
passed to the function. Here the dummy
arguments are declared as pointer to types that
match the data types of actual arguments.

16. Function call
Depending upon their inputs (i.e. parameters) and
outputs, functions are classified as:
 Function with no argument (I)& no return
value(O).
 Function with argument and no return value.
 Function with arguments and a return value.
 Function with no arguments and a return value.

17. Recursion
Recursion is a function who called function repeatedly
by itself. A recursive function may have following two
properties:
 A function must call itself
 There should be a stopping condition so that a
function should not call itself an infinite number of
times.

18. Array & Functions
Array can be passed to a function in C. An
array name can be used as an argument
for the declaration. No subscripts or
square brackets are required to invoke a
function using array.

19. Pointers
Just another kind of “placeholder” to hold “address” of
memory location.
 - Address is also a number
 - Itself resides on some memory location
Memory Address Value
0x8004 ….
0x8008 129
0x800C ….
0x8010 0x8008
0x8014 ...
variable A
address of A

20. Declaration of Pointer Variables
 Declare variables a, b
int a, b;
 Declare a pointer
int* pa;
 Set value of a
a = 10;
 Point pa to address of a
pa = &a;
 Set value of a using pa
*pa = 12; pa = &b;

21. Pointer Operators
 “address-of” operator: &
Gets address of a variable
De-referencing operator: *
- Accesses the memory location
this pointer holds address of

22. Pointer Arithmetic/Expressions
 Arithmetic operators work as usual on ordinary
data types.
int a = 1; a++; // a == 2
 It gets a bit complicated when arithmetic operators
are used on pointers
 int* p = 0x8004; p++;
 What does p hold now? 0x8005???
 Compiler knows that p is a pointer to integer type
data, so an increment to it should point to next
integer in memory. Hence 0x8008.

23. Pointers and Functions
 A function can be passed arguments usingbasic data
types
- int prod(int a, int b) { return a*b; }
 How to return multiple values from function?
- void prod_and_sum(int a, int b, int*p, int* s)
{ *p = a*b; *s = a+b; }

24. Pointers and Arrays
 Since arrays are a contiguous set of variables
 in memory, we can access them with pointers
 int arr[5];
 int *p = &arr[0];
 *(p+0) = 1; // arr[0]
 *(p+1) = 2; // arr[1]
 *(p+2) = 4; // arr[2]
 *(p+3) = 8; // arr[3]
 ...

25. Dynamic Memory Allocation
The process of allocating memory at run time is
known as dynamic memory allocation. Although
c does not inherently have this facility there
are four library routines which allow this
functions, which can be used to allocate and
free memory during the program execution.

26. Dynamic Memory Allocation Functions

27. sizeof()
sizeof() is a unary operator. This operator gives the size
of its argument in terms of bytes. The argument can
be variable, array or any data type(int, float, char
etc.). This operator also gives the size of any
structure.
Example-sizeof(
int);
This gives the bytes occupied by the int data type , that
is 2.

28. malloc()
A block of memory may be allocated using the function
malloc. The malloc function reserves a block of
memory of specified size and returns a pointer of
type void. This means that we can assign it to any type
of pointer. It takes the following form:
ptr=(cast-type*)malloc(byte-size);
ptr is a pointer of type cast-type the malloc returns a
pointer (of cast type) to an area of memory with size
byte-size

29. malloc() Example
Example:
x=(int*)malloc(100*sizeof(int));
On successful execution of this statement a
memory equivalent to 100 times the area of
int bytes is reserved and the address of the
first byte of memory allocated is assigned to
the pointer x of type int.

30. Calloc
 Calloc is another memory allocation function
that is normally used to request multiple
blocks of storage each of the same size and
then sets all bytes to zero. The general form
of calloc is:
ptr=(cast-type*) calloc(n,elem-size);
ptr=(int*)calloc(5,2)

31. Calloc(Contd.)
calloc() allocates contiguous space for n blocks
each size of elements size bytes. All bytes are
initialized to zero and a pointer to the first
byte of the allocated region is returned. If
there is not enough space a null pointer is
returned.

32. free()
Compile time storage of a variable is allocated
and released by the system in accordance with
its storage class. With the dynamic runtime
allocation, it is our responsibility to release
the space when it is not required.
free(ptr);
ptr is a pointer that has been created by using
malloc or calloc

33. realloc
The memory allocated by using calloc or malloc
might be insufficient or excess sometimes in
both the situations we can change the memory
size already allocated with the help of the
function realloc. This process is called
reallocation of memory. The general
statement of reallocation of memory is :
ptr=realloc(ptr,newsize);