Functions and pointers_unit_4

FUNCTION
 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 it
self. Instead its requests other program like entities –
called functions in C to get its tasks done.
 A function is a self contained block of statements that
perform a coherent task of same kind

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(), main()

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

Function
 Syntax for function definition
datatype function_name (parameters/arguments 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.

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.

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();
add();
}
void add() //called function
{
int a,b,c;
printf("nEnter two number:");
scanf("%d%d",&a,&b);
c=a+b;
printf("nSum is:%d",c);
}

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 as well as between
called function and calling 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);
printf("nSum is:%d",c);
}
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
#include <stdio.h>
#include<conio.h>
void main()
{
int x,y,change(int,int);
printf("nEnter value of x:");
scanf("%d",&x);
printf("nEnter value of y:");
scanf("%d",&y);
change(x,y);
printf("nnValues in the
Main()-->x=%d,y=%d",x,y);
}
int change(int a,int b)
{
int c;
c=a;
a=b;
b=c;
printf("nValues in the
Fuction --
>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=5,y=6

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,change(int*,int*);
printf("nEnter value of
x:");
scanf("%d",&x);
printf("nEnter value of
y:");
scanf("%d",&y);
change(&x,&y);
printf("nnValues in
the Main()--
>x=%d,y=%d",x,y);
}
int change(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

Sum of natural numbers using recursion
#include <stdio.h>
int sum(int n);
int main()
{
int number, result;
printf("Enter a positive integer: ");
scanf("%d", &number);
result = sum(number);
printf("sum = %d", result);
return 0;
}

int sum(int n)
{
if (n != 0) // sum() function calls itself
return n + sum(n-1);
else
return n;
}

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
 floor(x):
returns the largest integer value less than or equal to x.
example: floor(7.5) is 6
 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
 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

Computation of Sine Series
#include<stdio.h>
#include<conio.h>
void main()
{
int i, n;
float x, sum, t;
printf(" Enter the value for x : ");
scanf("%f",&x);
x=x*3.14159/180;
t=x;
sum=x;

/* Loop to calculate the value of Sine */
for(i=1;i<=n;i++)
{
t=(t*(-1)*x*x)/(2*i*(2*i+1));
sum=sum+t;
}
printf(" The value of Sin(%f) = %.4f",x,sum);
}

Random Number Generation
#include <stdio.h>
#include <stdlib.h>
#include <time.h>
// Generates and prints 'count' random
// numbers in range [lower, upper].
void printRandoms(int lower, int upper, int count)
{
int i;
for (i = 0; i < count; i++) {
int num = (rand() %(upper - lower + 1)) + lower;
printf("%d ", num);

int main()
{
int lower = 10, upper = 20, count = 1;
// Use current time as
// seed for random generator
srand(time(0));
printRandoms(lower, upper, count);
return 0;
}

#include<stdio.h>
void TOH(int n,char x,char y,char z)
{
if(n>0)
{
TOH(n-1,x,z,y);
printf("n%c to %c",x,y);
TOH(n-1,z,y,x);
}
}
int main()
{
int n=3;
TOH(n,'A','B','C');
}

Output
A to B
A to C
B to C
A to B
C to A
C to B
A to B

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

Example
#include<stdio.h>
#include<conio.h>
void main()
{
int a=10;
int *b,**c;
b=&a;
c=&b;
printf("n The Value of a = %d",a);
printf("n The Address of a = %u",&a);
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 a = 5001
The Value of b = 5001
The Address of b = 8000
The Value of c = 8000
The Address of c = 9000

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;
printf("n The Value of a[0] = %d",a[0]);
printf("n The Address of a[0] = %u",&a[0]);
printf("n The Value of b = %d",b);
}

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

Output
The Value of a[0] = 2
The Address of a[0] = 8744
The Value of b = 8744

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);
}

Pointer Arithmetic
 A pointer in c is an address, which is a numeric value.
 Therefore, you can perform arithmetic operations on a
pointer just as you can on a numeric value.
 here are four arithmetic operators that can be used on
pointers: ++, --, +, and –
 To understand pointer arithmetic, let us consider
that ptr is an integer pointer which points to the
address 1000. Assuming 32-bit integers, let us perform
the following arithmetic operation on the pointer −

ptr++
 After the above operation, the ptr will point to the
location 1004 because each time ptr is incremented, it
will point to the next integer location which is 4 bytes
next to the current location. This operation will move
the pointer to the next memory location without
impacting the actual value at the memory location.
If ptr points to a character whose address is 1000, then
the above operation will point to the location 1001
because the next character will be available at 1001.

Incrementing a Pointer
#include <stdio.h>
const int MAX = 3;
int main ()
{
int var[] = {10, 100, 200};
int i, *ptr; /* let us have array address in pointer */
ptr = var;
for ( i = 0; i < MAX; i++)
{
printf("Address of var[%d] = %xn", i, ptr );
printf("Value of var[%d] = %dn", i, *ptr ); /* move to the next location */
ptr++;
}
return 0;
}

Dynamic Memory Allocation
 Since C is a structured language, it has some fixed
rules for programming.
 One of it includes changing the size of an array.
 An array is collection of items stored at continuous
memory locations.

If there is a requirement to change this length (size). For
Example,
 If there is a situation where only 5 elements are needed
to be entered in this array. In this case, the remaining 4
indices are just wasting memory in this array. So there
is a requirement to lessen the length (size) of the array
from 9 to 5.
 Take another situation. In this, there is an array of 9
elements with all 9 indices filled. But there is a need to
enter 3 more elements in this array. In this case 3
indices more are required. So the length (size) of the
array needs to be changed from 9 to 12.
 This procedure is referred to as Dynamic Memory
Allocation in C.

 Therefore, C Dynamic Memory Allocation can be
defined as a procedure in which the size of a data
structure (like Array) is changed during the runtime.
 C provides some functions to achieve these tasks.
There are 4 library functions provided by C defined
under <stdlib.h> header file to facilitate dynamic
memory allocation in C programming. They are:
 malloc()
 calloc()
 free()
 realloc()


malloc()
 “malloc” or “memory allocation” method in C is
used to dynamically allocate a single large block of
memory with the specified size.
 It returns a pointer of type void which can be cast into
a pointer of any form.
 It initializes each block with default garbage value.
 Syntax
ptr = (cast-type*) malloc(byte-size)
Example:
ptr = (int*) malloc(100 * sizeof(int));

Note:
 If space is insufficient, allocation fails and returns a
NULL pointer.

#include <stdio.h>
#include <stdlib.h>
int main()
{
// This pointer will hold the
// base address of the block created
int* ptr;
int n, i;
// Get the number of elements for the array
n = 5;
printf("Enter number of elements: %dn", n);
// Dynamically allocate memory using malloc()
ptr = (int*)malloc(n * sizeof(int));
// Check if the memory has been successfully
// allocated by malloc or not
if (ptr == NULL) {
printf("Memory not allocated.n");
exit(0);

}
else {
// Memory has been successfully allocated
printf("Memory successfully allocated using malloc.n");
// Get the elements of the array
for (i = 0; i < n; ++i) {
ptr[i] = i + 1;
}
// Print the elements of the array
printf("The elements of the array are: ");
for (i = 0; i < n; ++i) {
printf("%d, ", ptr[i]);
}
}
return 0;
}

Output:
Enter number of elements: 5
Memory successfully allocated using malloc.
The elements of the array are: 1, 2, 3, 4, 5,

Calloc()
 “calloc” or “contiguous allocation” method in C
is used to dynamically allocate the specified
number of blocks of memory of the specified type.
It initializes each block with a default value ‘0’.
Syntax:
ptr = (cast-type*)calloc(n, element-size);
For Example:
ptr = (float*) calloc(25, sizeof(float));
 This statement allocates contiguous space in
memory for 25 elements each with the size of the
float.

Program:
#include <stdio.h>
#include <stdlib.h>
int main()
{
int* ptr;
int n, i;
n = 5;
// Dynamically allocate memory using calloc()
ptr = (int*)calloc(n, sizeof(int));
// allocated by calloc or not
if (ptr == NULL) {

exit(0);
}
else {
printf("Memory successfully allocated using calloc.n");
for (i = 0; i < n; ++i) {
ptr[i] = i + 1;
}
for (i = 0; i < n; ++i) {
}
}
return 0; }

cfree()
 “free” method in C is used to dynamically de-allocate the memory.
 The memory allocated using functions malloc() and calloc() is not de-
allocated on their own.
 Hence the free() method is used, whenever the dynamic memory
allocation takes place. It helps to reduce wastage of memory by freeing it.
Syntax:
free(ptr);

Program
#include <stdio.h>
#include <stdlib.h>
int main()
{
int *ptr, *ptr1;
int n, i;
n = 5;
// Dynamically allocate memory using malloc()
ptr = (int*)malloc(n * sizeof(int));
ptr1 = (int*)calloc(n, sizeof(int));

if (ptr == NULL || ptr1 == NULL) {
exit(0);
}
else {
printf("Memory successfully allocated using malloc.n");
// Free the memory
free(ptr);
printf("Malloc Memory successfully freed.n");
printf("nMemory successfully allocated using calloc.n");

// Free the memory
free(ptr1);
printf("Calloc Memory successfully freed.n");
}
return 0;
}

realloc()
 “realloc” or “re-allocation” method in C is used to
dynamically change the memory allocation of a
previously allocated memory.
 In other words, if the memory previously allocated with
the help of malloc or calloc is insufficient, realloc can be
used to dynamically re-allocate memory.
 re-allocation of memory maintains the already present
value and new blocks will be initialized with default
garbage value.
Syntax:
ptr = realloc(ptr, newSize); where ptr is reallocated with new
size 'newSize'.

Program:
#include <stdio.h>
#include <stdlib.h>
int main()
{
int* ptr;
int n, i;
n = 5;
ptr = (int*)calloc(n, sizeof(int));

if (ptr == NULL) {
exit(0);
}
else {
printf("Memory successfully allocated using calloc.n");
for (i = 0; i < n; ++i) {
ptr[i] = i + 1;
}
for (i = 0; i < n; ++i) {
}

// Get the new size for the array
n = 10;
printf("nnEnter the new size of the array: %dn", n);
// Dynamically re-allocate memory using realloc()
ptr = realloc(ptr, n * sizeof(int));
printf("Memory successfully re-allocated using
realloc.n");
// Get the new elements of the array
for (i = 5; i < n; ++i) {
ptr[i] = i + 1;
}
for (i = 0; i < n; ++i) {
}

Card Shuffling and Dealing Simulation
 Collection of playing cards is known as deck
 A deck of card contains 52 cards.
 There are 4 suits and each 4 suits contains 13 faces
 The 4 suits are
 Hearts, Diamonds, Clubs, Spades
The 13 faces are
Ace, Deuce, Three, Four, Five, Six, Seven, Eight, Nine,
Ten, Jack, Queen, King

Program:
#include <stdio.h>
#include <stdlib.h>
#include <time.h> /*…Used to count time …*/
void shuffle( int [][ 13 ] );
void deal( const int [][ 13 ], const char *[], const char *[] );
void main()
{
const char *suit[ 4 ] = { “Hearts”, “Diamonds”, “Clubs”, “Spades” };
const char *face[ 13 ] = { “Ace”, “Deuce”, “Three”, “Four”, “Five”, “Six”,
“Seven”, “Eight”, “Nine”, “Ten”, “Jack”, “Queen”, “King” };
int deck[ 4 ][ 13 ] = { 0 };
srand( time( 0 ) );
shuffle( deck );
deal( deck, face, suit );
} /*…Main Function Ends..*/

void shuffle( int wDeck[][ 13 ] ) /*….Function Definition…*/
{
int row, column, card;
for ( card = 1; card <= 52; card++ )
{
do {
row = rand() % 4;
column = rand() % 13;
} while( wDeck[ row ][ column ] != 0 );
wDeck[ row ][ column ] = card;
}
} /*…Loop End’s…*/

void deal( const int wDeck[][ 13 ], const char *wFace[],const char *wSuit[] )
{
int card, row, column;
for ( card = 1; card <= 52; card++ )
for ( row = 0; row <= 3; row++ )
for ( column = 0; column <= 12; column++ )
if ( wDeck[ row ][ column ] == card )
printf( “%5s of %-8s%c”,
wFace[ column ], wSuit[ row ],
card % 2 == 0 ? ‘n’ : ‘t’ );
}

Functions and pointers_unit_4

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