Functions and pointers_unit_4

FUNCTION
 A function is a group of statements that together perform
a task. (or) A Function is a sub-program, which
contains one or more statements and it performs some
task when its called.
 A computer program cannot handle all the tasks by itself.
Instead its requests other program like entities – called
functions in C to get its task done.

Why we use functions?
 Writing functions avoids rewriting the same code over and
over.
 Suppose that there is a section of code in a program that
calculates area of a circle. If later in the program we want to
calculate the area of a different circle, we wont like to write
the same instructions again.
 Instead, we would prefer to jump to a “section of code” that
calculates area and then jump back to the place from where
we left off.
 This section of code is nothing but a function.

 Using functions it becomes easier to write programs and keep
track of what they are doing.
 If the operation of a program can be divided in to separate
activities, and each activity placed in a different function, then
each could be written and checked more or less independently.
 Separating the code in to modular functions also makes the
pro-gram easier to design and understand.
Why we use functions?

TYPES
 There are two different types of functions:
 Pre-defined functions
 User-defined functions

Pre-Defined Functions
 The pre-defined functions or library functions are
built-in functions.
 The user can use the functions, but cannot modify
those functions.
 Example: sqrt()

User-Defined Functions
 The functions defined by the user for their
requirements are called user-defined functions.
 Whenever it is needed, the user can modify this
function.
 Example: sum(a,b)

Advantage of User-Defined Functions
 The length of the source program can be reduced.
 It is easy to locate errors.
 It avoids coding of repeated instructions.

Elements of User-Defined Function
 Function declaration
 Function definition
 Function call
#include <stdio.h>
#include<conio.h>
void main()
{
void add(void); //function declaration
add(); //function call
}
void add() // function definition
{
int a,b,c;
printf("nEnter two number:");
scanf("%d%d",&a,&b);
c=a+b;
printf("nSum is:%d",c);
}

Function
 Syntax
datatype function_name (parameters list)
{
local variable declaration;
…………………………
body of the function;
…………………………
return(expression);
}

How Function Works?
 Once a function is called the control passes to the called function.
 The working of calling function is temporarily stopped.
 When the execution of called function is completed then the
control returns back to the calling function and executes the next
statement.

Parameters
 Actual Parameter
These are the parameters which are transferred from the
calling function to the called function.
 Formal Parameter
These are the parameters which are used in the called
function.
Parameter is variable in the declaration of function.
Argument is the actual value of this variable that gets
passed to function.

return Statement
 The return statement may or may not send some
values to the calling function.
 Syntax:
return; (or)
return (expression);

Function Prototypes
There are four types:
 Function with no arguments and no return values.
 Function with arguments and no return values.
 Function with arguments and return values.
 Function with no arguments and with return values.
Argument is the actual value of the variable that gets
passed to function.

Function with no arguments and no return
values
 Here no data transfer takes place between the calling
function and the called function.
 These functions act independently, i.e. they get input
and display output in the same block.

Example
#include <stdio.h>
#include<conio.h>
void main() //calling function
{
void add(void);
add();
}
void add() //called function
{
int a,b,c;
c=a+b;
}

Output
Enter two number:3
4
Sum is:7

Function with arguments and no return values
 Here data transfer take place between the calling function
and the called function.
 It is a one way data communication, i.e. the called
program receives data from calling program but it does not
return any value to the calling program.

Example
#include <stdio.h>
#include<conio.h>
void main()
{
int a,b;
void add(int,int);
add(a,b);
}
void add(int x,int y) //function with arguments
{
int z;
z=x+y;
printf("nSum is:%d",z);
}

Output
Enter two number:2
4
Sum is:6

Function with arguments
and return values
 Here data transfer takes place between the calling
function and the called function.
 It is a two way data communication, i.e. the called
program receives data from calling program and it
returns some value to the calling program.

Example
#include <stdio.h>
#include<conio.h>
void main()
{
int a,b,c;
int add(int,int);
c=add(a,b);
}
int add(int x,int y)
{
int z;
z=x+y;
return(z);
}

Output
Enter two number:6
7
Sum is:13

Function with no arguments
and with return values
 Here data transfer takes place between the called
function and the calling function.
 It is a one way data communication, i.e. the called
program does not any receive data from the calling
program but it returns some value to the calling
program.

Example
#include <stdio.h>
#include<conio.h>
void main()
{
int add(),d;
d=add();
printf("nSum is:%d",d);
}
int add() //function with no argument
{
int a,b,c;
c=a+b;
return(c);
}

Output
Enter two number:5
8
Sum is:13

Parameter Passing Methods
 There are two different ways of passing parameters to a
method, they are:
 Call by value
 Call by reference

Call by value
 Actual arguments are passed to the formal arguments.
 Any changes made to the formal argument does not
affect the actual argument.

Example-swapping
#include <stdio.h>
#include<conio.h>
void main()
{
int x,y;
int swap(int,int);
printf("nEnter value of x:");
scanf("%d",&x);
printf("nEnter value of y:");
scanf("%d",&y);
swap(x,y);
printf("nnValues in the
Main()-->x=%d,y=%d",x,y);
}
int swap(int a,int b)
{
int c;
c=a;
a=b;
b=c;
printf("nValues in the Fuction -->
x=%d, y=%d",a,b);
}
Output:

Call by reference
 Instead of passing values, the address of the argument
will be passed.
 Any changes made to the formal argument will affect
the actual argument.

Example
#include <stdio.h>
#include<conio.h>
void main()
{
int x,y;
int swap(int*,int*);
printf("nEnter value of x:");
scanf("%d",&x);
printf("nEnter value of y:");
scanf("%d",&y);
// address of x and y is passed to the
swap function
swap(&x,&y);
printf("nnValues in the Main-->
x=%d, y=%d",x, y);
}
//pointer a and b points to the address
of x and y respectively.
int swap(int *a, int *b)
{
int c;
c=*a;
*a=*b;
*b=c;
printf("nValues in the Function -->
x=%d,y=%d",*a,*b);
}
output:
Enter value of x:5
Enter value of y:6
Values in the Function -->x=6,y=5
Values in the Main-->x=6,y=5

Recursion
 It is a process of calling the same function itself again and
again until some condition is satisfied.
Syntax:
func1()
{
………..
func1();
…………
}

Example
#include<stdio.h>
#include<conio.h>
void main()
{
int a;
int rec(int);
printf("nEnter the number:");
scanf("%d",&a);
printf("The factorial of %d! is
%d",a,rec(a));
}
int rec(int x)
{
int f;
if(x==1)
return(1);
else
f=x*rec(x-1);
return(f);
}
Output:
Enter the number:5
The factorial of 5! is 120

Library Function
 Library functions are the pre-defined functions.
 The library function provides functions like
mathematical, string manipulation etc,.
 In order to use a library function, it is necessary to call
the appropriate header file at the beginning of the
program.
 The header file informs the program of the name,
type, and number and type of arguments, of all of the
functions contained in the library in question.
 A header file is called via the preprocessor statement.

Some Examples of Library
Functions
 sqrt(x):
It is used to find the square root of x
Example: sqrt(36) is 6
 abs(x):
It is used to find the absolute value of x
Example: abs(-36) is 36
 pow(x,y):
It is used to find the value of xy
Example: pow(5,2) is 25

 ceil(x):
It is used to find the smallest integer greater than or equal to x.
Example: ceil(7.7) is 8
 rand():
It is used to generate a random number.
 sin(x):
It is used to find the sine value of x
Example: sin(30) is 0.5
 cos (x):
It is used to find the cosine value of x
Example: cos(30) is 0.86

 tan(x):
It is used to find the tan value of x
Example: tan(30) is 0.577
 toascii(x):
It is used to find the ASCII value of x
Example: toascii(a) is 97
 toupper(x):
It is used to convert lowercase character to uppercase.
Example: toupper(‘a’) is A toupper(97) is A
 tolower(x):
It is used to convert uppercase character to lowercase.
Example: tolower(‘A’) is a

Example:
#include<stdio.h>
#include<conio.h>
#include<math.h>
#include<ctype.h>
void main()
{
int x,y=2;
printf("nEnter the number:");
scanf("%d",&x);
printf("nThe square root of %d is %f",x,sqrt(x));
printf("nThe value of %d power%dis%f ",x,y,pow(6,2));
printf("nThe ceiling of 6.7 is %f",ceil(6.7));
printf("nThe floor of 6.7 is %f",floor(6.7));

printf("nThe absolute value of -6 is %d",abs(-6));
printf("nThe value of sin 45 is %f",sin(45));
printf("nThe uppercase of 'a' is %c",toupper('a'));
printf("nThe uppercase of 97 is %c",toupper(97));
getch();
}

Output:
Enter the number:6
The square root of 6 is 2.449490
The value of 6 power 2 is 36.000000
The ceiling of 6.7 is 7.000000
The floor of 6.7 is 6.000000
The absolute value of -6 is 6
The value of sin 45 is 0.850904
The uppercase of 'a' is A
The uppercase of 97 is A

Average of array Elements using user
defined function

To Find the length of the string
with user defined function

The Towers of Hanoi
A Recursion Application
 GIVEN: three poles
 a set of discs on the first pole, discs of different sizes, the
smallest discs at the top
 GOAL: move all the discs from the left pole to the right one.
 CONDITIONS: only one disc may be moved at a time.
 A disc can be placed either on an empty pole or on top of a
larger disc.

Random number generation using recursion function
#include <stdio.h>
#include <stdlib.h>
int main()
{
void random(void);
int c, n;
printf("Ten random numbers in [1,100]n");
for (c = 1; c <= 10; c++)
{
random();
}
return 0;
}
void random()
{
int n;
n = rand()%100 + 1;
printf("%dn", n);
}

Pointers
 Pointer is a variable that contains the address of
another variable i.e.. direct address of the memory
location.
 Like any variable or constant, you must declare a
pointer before you can use it to store any variable
address.

Example:
x=5
x Variable
1002 Address
5 Value

Example
#include<stdio.h>
#include<conio.h>
void main()
{
int x=5;
printf("n The Address of x = %u",&x);
printf("n The Value of x = %d",x);
}
Output
The Address of x = 8714
The Value of x = 5

Pointer Declaration
 Syntax:
data-type *pointer-name;
data-type - Type of the data to
which the pointer points.
pointer-name - Name of the pointer
 Example: int *a;

Accessing Variable through Pointer
 If a pointer is declared and assigned to a variable, then
the variable can be accessed through the pointer.
 Example:
int *a;
x=5;
a=&x;

Example
#include<stdio.h>
#include<conio.h>
void main()
{
int y=10;
int *a;
a=&y;
printf("n The Value of y = %d",y);
printf("n The Address of y = %u",&y);
printf("n The Value of a = %d",a);
printf("n The Address of a = %u",&a);
}

Illustration of the example:
5001 10
8000
a y
5001
Variable
Value
Address

Output
The Value of y = 10
The Address of y = 5001
The Value of a = 5001
The Address of a = 8000

Null Pointer
 A pointer is said to be null pointer if zero is assigned to
the pointer.
 For Example:
int *a,*b;
a=b=0;

Pointer to Pointer
 Here one pointer stores the address of another pointer
variable.
 Example:
int x=10,*a,**b;
a=&x;
b=&a;

 Illustration:
5001 10
8000
a x
5001
Variable
Value
Address
8000
9000
b

Output:
The Value of a[0] = 2
The Address of a[0] = 6356736
The Value of b = 6356736

Example
#include<stdio.h>
#include<conio.h>
void main()
{
int a=10;
int *b,**c;
b=&a;
c=&b;
printf("n The Value of b = %d",b);
printf("n The Address of b = %u",&b);
printf("n The Value of c = %d",c);
printf("n The Address of c = %u",&c);
}

Output
The Value of a = 10
The Address of b = 8000
The Value of c = 8000
The Address of c = 9000

#include<stdio.h>
#include<conio.h>
void main()
{
int a=10;
int *b,**c;
b=&a;
c=&b;
printf("n The Address of b = %u",&b);
printf("n The Value of c = %d",c);
printf("n The Address of c = %u",&c);
printf("n The value of b = %d",*b);
printf("n The value of c = %d",*c);
printf("n The value c = %d",**c);
}
output:
The Value of a = 10

Output:
The Value of a = 10

Pointers and Arrays
 The elements of the array can also be accessed through
a pointer.
 Example
int a[3]={2,3,7};
int *b;
b=a;

Example 1
#include<stdio.h>
#include<conio.h>
void main()
{
int a[3]={2,3,7};
int *b;
b=a; or b=&a;
printf("n The Value of a[0] = %d",a[0]);
printf("n The Address of a[0] = %u",&a[0]);
}

 Illustration of the example:
8744 2
9000
b a[0]
8744
Variable
Value
Address

Output

#include<stdio.h>
#include<conio.h>
void main()
{
int a[3]={2,3,7};
int *b;
b=&a;
}

Example 2
#include<stdio.h>
#include<conio.h>
void main()
{
int a[5]={2,3,7,9,10};
int i;
for(i=0;i<5;i++)
{
printf("n The Value of a[%d] = %d",i,a[i]);
printf("n The Address of a[%d] = %u",i,&a[i]);
}
}

Illustration of the example:
2 3 7 9 10
a[0] a[1] a[2] a[3] a[4]
8724 8726 8728 8730 8732
Array
Value
Address

Output

Example 3
#include<stdio.h>
#include<conio.h>
void main()
{
int a[5]={1,2,3,4,5};
int i,sum=0;
int *b;
b=a;
for(i=0;i<5;i++)
{
sum=sum + *b;
b++; //b=b+1
}
printf("n The Sum is %d",sum);
}

Pointers and Structures
 Syntax:
struct structure_name
{
structure element1;
structure element2;
…………………….
}variable,*ptr;

 A sample code illustrating pointers and structure
struct stud
{
int sno;
char name[10];
int mark;
};
struct stud *s;

Example
#include<stdio.h>
#include<conio.h>
struct stud
{
int regno;
char name[10];
int m1;
int m2;
int m3;
};
struct stud s;
struct stud *t;

void main()
{
float tot,avg;
t=&s;
printf("nEnter the student regno,name,m1,m2,m3:");
scanf("%d%s%d%d%d",&s.regno,&s.name,&s.m1,&s.m2,&s.m3);
tot=s.m1+s.m2+s.m3;
avg=tot/3;
printf("nThe student Details are:");
printf("n%dt%st%ft%f",s.regno,s.name,tot,avg);
printf("n%dt%st%ft%f",t->regno,t->name,tot,avg);
}

Output
Enter the student regno,name,m1,m2,m3:1
aaa
76
89
76
The student Details are:
1 aaa 241.000000 80.333336
1 aaa 241.000000 80.333336

Functions and pointers_unit_4

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