Control Statements, Array, Pointer, Structures

CONTROL STATEMENTS, ARRAY,
POINTER, STRUCTURES
UNIT- II
Fundamental of Computer
programming -206

By- Er. Indrajeet Sinha , +919509010997
UNIT-II
2.1- Control Statements
2.2- Switch statement
2.3- Loop Control Statement
2.4- Array in C
2.5- Strings
2.6- Pointers, Address Arithmetic
2.7- Pointers to represent array
2.8- Command line arguments
2.9- Structures, typedef
2

2.1 - CONTROL
STATEMENTS IN C
Lecture no.- 13,
UNIT- II

2.1.1- INTRODUCTION
 A control statement is a statement that
determines whether other statements will be
executed.
 An if statement decides whether to execute
another statement, or decides which of
two statements to execute.
 A loop decides how many times to execute
another statement.
4

C KEYWORDS
auto double int struct
break else long switch
case enum register typedef
char extern return union
const float short unsigned
continue for signed void
default goto sizeof volatile
do if static while
The words in bold print are used in control statements. They change the
sequential execution of the assignment statements in a function block

C CONTROL STATEMENT
 If Statement
 If / else statement
 For loop
 Do loop
 Do While Loop
Definition:-
Control statements enable us to specify the flow of program control; ie, the
order in which the instructions in a program must be executed. They make
it possible to make decisions, to perform tasks repeatedly or to jump from
one section of code to another.

2.1.2 - IF SELECTION STRUCTURE
 Selection structure
 Choose among alternative courses of action
 Pseudocode example:
If student’s grade is greater than or equal to 60
Print “Passed”
 If the condition is true
 Print statement executed, program continues to next
statement
 If the condition is false
 Print statement ignored, program continues
 Indenting makes programs easier to read

IF SELECTION STRUCTURE
 Flowchart of pseudocode statement
A decision can be made on
any expression.
zero - false
nonzero - true
Example:
3 - 4 is true
true
false
grade >= 60 print “Passed”

2.1.2- “IF” – “ELSE” WITH A BLOCK OF
STATEMENTS
if (aValue <= 10)
{
printf("Answer is %8.2fn", aValue);
countB++;
} // End if
else
{
printf("Error occurredn");
countC++;
} // End else

2.1.3 IMPORTANCE OF BRACES ( { } )
 Curly braces (also referred to as just "braces" or
as "curly brackets") are a major part of the C
programming language.
 The main uses of curly braces in:
 Functions
void myfunction(datatype argument)
{
statements(s)
}
 Loops
 Conditional statements

2.1.4 - NESTED “IF” STATEMENT
if (aValue == 1)
countA++;
else if (aValue == 10)
countB++;
else if (aValue == 100)
countC++;
else
countD++;

EXAMPLE IF- ELSE
12
// Program to display a number if user enters negative number
// If user enters positive number, that number won't be displayed
#include <stdio.h>
int main()
{
int number;
printf("Enter an integer: ");
scanf("%d", &number);
// Test expression is true if number is less than 0
if (number < 0)
{
printf("You entered %d.n", number);
}
printf("The if statement is easy.");
return 0;
}
Output 1
Enter an integer: -2
You entered -2.

SWITCH STATEMENT
Lecture no.- 14,
UNIT- II

2.1.5- SWITCH STATEMENT
14
 Definition:-
 A switch statement is a type of selection control
mechanism used to allow the value of a variable or
expression to change the control flow of program
execution via a multiway branch.
 A switch statement allows a variable to be tested for
equality against a list of values. Each value is called
a case, and the variable being switched on is
checked for each switch case.
 Switch case statements mostly used when we have
number of options (or choices) and we may need to
perform a different task for each choice.

SYNTAX OF SWITCH...CASE
15
 switch (n)
{
case constant1:
// code to be executed if n is equal to constant1;
break;
case constant2:
// code to be executed if n is equal to constant2;
break; . . .
default:
// code to be executed if n doesn't match any Constant
}

“SWITCH” STATEMENT
switch (aNumber)
{
case 1 : countA++;
break;
case 10 : countB++;
break;
case 100 :
case 500 : countC++;
break;
default : countD++;
} // End switch


FLOW CHART OF SWITCH
STATEMENT
17

2.1.6 PROBLEMS ON CONDITIONAL
STATEMENTS
18
# include <stdio.h>
int main() {
char operator;
double firstNumber,secondNumber;
printf("Enter an operator (+, -, *, /): ");
scanf("%c", &operator);
printf("Enter two operands: ");
scanf("%lf %lf",&firstNumber, &secondNumber);

switch(operator)
{
case '+':
printf("%.1lf + %.1lf = %.1lf",firstNumber, secondNumber,
firstNumber+secondNumber);
break;
case '-':
printf("%.1lf - %.1lf = %.1lf",firstNumber, secondNumber, firstNumber-
secondNumber); break;
PROGRAM TO CREATE A SIMPLE CALCULATOR
// PERFORMS ADDITION, SUBTRACTION, MULTIPLICATION OR
DIVISION DEPENDING THE INPUT FROM USER

CONT…
19
case '*':
printf("%.1lf * %.1lf = %.1lf",firstNumber, secondNumber,
firstNumber*secondNumber);
break;
case '/':
printf("%.1lf / %.1lf = %.1lf",firstNumber, secondNumber,
firstNumber/firstNumber);
break;
// operator is doesn't match any case constant (+, -, *, /)
default:
printf("Error! operator is not correct");
}

return 0;
}
Output-
Enter an operator
(+, -, *,): -
Enter two operands:
32.5
12.4
32.5 - 12.4 = 20.1

LOOP CONTROL
STATEMENT
Lecture no.- 15,
UNIT- II

2.2.1 INTRODUCTION OF LOOPS
 Definition
 Repeats a statement or group of statements
while a given condition is true. It tests the
condition before executing the loop body.
 loop. Executes a sequence of statements
multiple times and abbreviates the code that
manages the loop variable.
 Loops are used in programming to repeat a
specific block of code. After reading this
tutorial, you will learn to create a for loop in
C programming.
for loop
while loop
do...while loop
21

2.2.2 INITIALIZATION, TEST
CONDITION, INCREMENT AND
DECREMENT OF LOOPS
Note:- A sequence of statements are executed until a specified
condition is true. This sequence of statements to be executed
is kept inside the curly braces { } known as the Loop body.
After every execution of loop body, condition is verified, and if
it is found to be true the loop body is executed again. When
the condition check returns false, the loop body is not
executed.
22

2.2.3- FOR LOOP
 A for loop is a repetition control structure that
allows us to efficiently write a loop that needs to
execute a specific number of times.
 Syntax
for ( init; condition; increment )
{
statement(s);
}
 Here is the flow of control in a 'for' loop −
 The init step is executed first, and only once. This
step allows you to declare and initialize any loop
control variables. You are not required to put a
statement here, as long as a semicolon appears.
23

 Next, the condition is evaluated. If it is true, the
body of the loop is executed. If it is false, the body of
the loop does not execute and the flow of control
jumps to the next statement just after the 'for' loop.
 After the body of the 'for' loop executes, the flow of
control jumps back up to the increment statement.
This statement allows you to update any loop control
variables. This statement can be left blank, as long
as a semicolon appears after the condition.
 The condition is now evaluated again. If it is true, the
loop executes and the process repeats itself (body of
loop, then increment step, and then again condition).
After the condition becomes false, the 'for' loop
terminates. 24

 Flow Diagram
25

EXAMPLE FOR LOOP
#include <stdio.h>
int main ()
{
int a; /* for loop execution */
for( a = 10; a < 20; a = a + 1 )
{
printf("value of a: %dn", a);
}
return 0;
}
26
Out Put:
value of a: 10
value of a: 11
value of a: 12
value of a: 13
value of a: 14
value of a: 15
value of a: 16
value of a: 17
value of a: 18
value of a: 19

 for” with a single statement
 for” with a block of statements
27
for (i = 1; i <= MAX_LENGTH; i++)
printf("#");
for (i = 0; i < MAX_SIZE; i++)
{
printf("Symbol is %cn", aBuffer[i]);
aResult = aResult / i;
} // End for

WHILE LOOP
Lecture no.- 17,
UNIT- II

2.2.5- WHILE LOOP
 A while loop in C programming repeatedly
executes a target statement as long as a given
condition is true.
 Syntax
while(condition)
{
statement(s);
}
 Here, statement(s) may be a single statement or a block of
statements. The condition may be any expression, and true
is any nonzero value. The loop iterates while the condition is
true.
 When the condition becomes false, the program control passes
to the line immediately following the loop.
29

 Flow Diagram
30
Here, the key point
to note is that a
while loop might
not execute at all.
When the condition
is tested and the
result is false, the
loop body will be
skipped and the
first statement
after the while loop
will be executed.

Example While Loop
#include <stdio.h>
int main ()
{ /* local variable definition */
int a = 10; /* while loop execution */
while( a < 20 )
{
printf("value of a: %dn", a); a++;
} return 0;
}
31
Out Put:
value of a: 10
value of a: 11
value of a: 12
value of a: 13
value of a: 14
value of a: 15
value of a: 16
value of a: 17
value of a: 18
value of a: 19

2.2.6- DO-WHILE LOOP
 Unlike for and while loops, which test the loop condition at
the top of the loop, the do...while loop in C programming
checks its condition at the bottom of the loop.
 A do...while loop is similar to a while loop, except the fact
that it is guaranteed to execute at least one time.
 Syntax
do
{
statement(s);
} while
 Notice that the conditional expression appears at the end of the loop,
so the statement(s) in the loop executes once before the condition is
tested.
 If the condition is true, the flow of control jumps back up to do, and
the statement(s) in the loop executes again. This process repeats until
the given condition becomes false.
32

 Flow Diagram
33

 Example
#include <stdio.h>
int main ()
int a = 10; /* do loop execution */
do
{
printf("value of a: %dn", a);
a = a + 1;
}while( a < 20 );
return 0;
}
34
Out Put:
value of a: 10
value of a: 11
value of a: 12
value of a: 13
value of a: 14
value of a: 15
value of a: 16
value of a: 17
value of a: 18
value of a: 19

NESTED LOOPS
(FOR,WHILE,DO-WHILE)
Lecture no.- 18,
UNIT- II

2.2.8 - NESTED LOOPS (FOR,WHILE,DO-
WHILE)
 C programming allows to use one loop inside another loop.
 On loop nesting is that we can put any type of loop inside
any other type of loop. For example, a 'for' loop can be
inside a 'while' loop or vice versa.
 Syntax
 The syntax for a nested for loop statement in C is
as follows −
{
{
statement(s);
}
statement(s);
}
36

 The syntax for a nested while loop statement in
C programming language is as follows −
while(condition)
{ while(condition)
{
statement(s);
}
statement(s);
}
37

 The syntax for a nested do...while loop statement in
C programming language is as follows −
do
{
statement(s);
do
{
statement(s);
}while( condition );
}while( condition );
38

 Example
 The following program uses a nested for loop to find the prime
numbers from 2 to 100 −
#include <stdio.h>
int main ()
int i, j; for(i = 2; i<100; i++)
{
for(j = 2; j <= (i/j); j++)
if(!(i%j))
break; // if factor found, not prime
if(j > (i/j))
printf("%d is primen", i);
}
return 0;
}
39
OutPut:
2 is prime
3 is prime
5 is prime
7 is prime
11 is prime
13 is prime
17 is prime
19 is prime
23 is prime
29 is prime
31 is prime
.
.
.
89 is prime
97 is prime

ARRAY IN C
Lecture no.- 19,
UNIT- II

INTRODUCTION OF LECTURE
 What is Array?
 Arrays a kind of data structure that can store a fixed-
size sequential collection of elements of the same type.
 An array is used to store a collection of data, but it is
often more useful to think of an array as a collection of
variables of the same type.
 All arrays consist of contiguous memory locations. The
lowest address corresponds to the first element and the
highest address to the last element.

41

 Array – In the C programming language an
array is a fixed sequenced collection of elements
of the same data type. It is simply a grouping of
like type data. In the simplest form, an array can
be used to represent a list of numbers, or a list of
names. Some examples where the concept of an
array can be used:
 List of temperatures recorded every hour in a day , or a
month, or a year.
 List of employees in an organization
 List of products and their cost sold by a store
42

 Since an array provides a convenient structure for
representing data, it is classified as one of the data
structures in C language.
 There are following types of arrays in the C
programming language –
 One – dimensional arrays
 Two – dimensional arrays
 Multidimensional arrays
43

2.3.1 ONE-DIMENSIONAL ARRAY
 Definition
 A list of items can be given one variable name using only
one subscript and such a variable is called single sub-
scripted variable or one dimensional array.
 2.3.2 Declaration of 1D Arrays –
 Like any other variable, arrays must be declared
before they are used so that the compiler can allocate
space for them in the memory. The syntax form of
array declaration is –
 Syntax
Datatype arrayName [ arraySize ];
 This is called a single-dimensional array.
The arraySize must be an integer constant greater
than zero and type can be any valid C data type.

44

 Example –
 float height[50];
 int groupt[10];
 char name[10]
 Now as we declare a array
 int number[5];
 Then the computer reserves five storage locations as the size of
the array is 5 as shown below –
45

 Initialization of 1D Array
 After an array is declared, it’s elements must be initialized.
In C programming an array can be initialized at either of
the following stages:
 At compile time
 At run time
 Compile Time initialization
 We can initialize the elements of arrays in the same was as
the ordinary variables when they are declared. The general
form of initialization of array is:
 type array-name[size] = { list of values };The values in the
list are separated by commas. For ex, the statement
 int number[3] = { 0,5,4 };
46

 Run time Initialization
 An array can also be explicitly initialized at run time.
For ex – consider the following segment of a C program.
for(i=0;i<10;i++)
{
scanf(" %d ", &x[i] );
}
 Above example will initialize array elements with the values
entered through the keyboard. In the run time initialization of
the arrays looping statements are almost compulsory. Looping
statements are used to initialize the values of the arrays one
by one by using assignment operator or through the keyboard
by the user.
47

 Simple C program to store the elements in the array and to print
them from the array.
#include<stdio.h>
void main()
{
int array[5],i;
printf("Enter 5 numbers to store them in array n");
for(i=0;i<5;i++)
{
scanf("%d",&array[i]);
}
printf("Element in the array are - n n");
for(i=0;i<5;i++)
{
printf("Element stored at a[%d] = %d n",i,array[i]);
} getch();
}
48
Input – Enter 5
elements in the array
– 23 45 32 25 45
Output – Elements
in the array are –
Element stored at
a[0]-23
Element stored at
a[0]-45
Element stored at
a[0]-32
Element stored at
a[0]-25
Element stored at
a[0]-45

2.3.4 TWO-DIMENSIONAL ARRAY
 Definition
 2D Arrays- There could be situations where a table of values will have to be
stored. In such cases 1D arrays are of no use. So we use 2D arrays to
represent the items in tables.
 Declaration
 syntax –
 type array_name [row_size][column_size];
 Initializing 2D Array
 Like the one dimensional array, 2D arrays can be initialized in both
the two ways; the compile time initialization and the run time
initialization.
 Compile Time initialization – We can initialize the elements of
the 2D array in the same way as the ordinary variables are
declared. The best form to initialize 2D array is by using the matrix
form. Syntax is as below –
 int table-[2][3] = { { 0, 2, 5} { 1, 3, 0} }; 49

 Run Time initialization – As in the initialization of 1D
array we used the looping statements to set the values of the
array one by one.
In the similar way 2D array are initialized by using the
looping structure.
Initialization method –
for(i=0;i<3;i++)
     {
for(j=0;j<3;j++)
           {
scanf("%d",&ar1[i][j]);
}      }
50

 Sample 2D array Program
#include<stdio.h>
#include<conio.h>
void main()
{
int array[3][3],i,j,count=0; /* Run time Initialization */
for(i=1;i<=3;i++)
{
for(j=1;j<=3;j++)
{
count++; array[i][j]=count;
printf("%d t",array[i][j]);
}
printf("n");
}
getch(); }
51
Output –
1    2    3
4      5      6
7      8      9

STRING IN C
Lecture no.- 23,
UNIT- II

2.11- INTRODUCTION OF LECTURE
 Definition
 Strings are actually one-dimensional array of
characters terminated by a null character '0'.
 In C programming, array of character are
called strings.
53

2.3.7 STRINGS – DECLARATION,
INITIALIZATION, READING,
PRINTING
 Declaration and initialization of String
 The following declaration and initialization create a
string consisting of the word "Hello". To hold the null
character at the end of the array, the size of the
character array containing the string is one more than
the number of characters in the word "Hello.“
 Syntax
 char greeting[6] = {'H', 'e', 'l', 'l', 'o', '0'};
 OR
 char greeting[] = "Hello";
54

 Following is the memory presentation of the above
defined string in C
 Note: The C compiler automatically places the '0'
at the end of the string when it initializes the
array. 55

Programming. Ex-
#include <stdio.h>
int main ()
{
char greeting[6] = {'H', 'e', 'l', 'l', 'o', '0'};
printf("Greeting message: %sn", greeting );
return 0;
}
Output:
Greeting message: Hello
56

2.3.8- STANDARD LIBRARY
FUNCTION OF STRING
57
Note:Where S1 and S2 are two different string.
S.N. Function Purpose
1 strcpy(s1, s2); Copies string s2 into string s1.
2 strcat(s1, s2); Concatenates string s2 onto the end of string
s1.
3 strlen(s1); Returns the length of string s1.
4 strcmp(s1, s2); Returns 0 if s1 and s2 are the same; less than
0 if s1<s2; greater than 0 if s1>s2.
5 strchr(s1, ch); Returns a pointer to the first occurrence of
character ch in string s1.
6 strstr(s1, s2); Returns a pointer to the first occurrence of
string s2 in string s1.

 Programming Example
#include <stdio.h>
#include <string.h>
int main ()
{
char str1[12] = "Hello";
char str2[12] = "World";
char str3[12]; int len ; /* copy str1 into str3 */
strcpy(str3, str1);
printf("strcpy( str3, str1) : %sn", str3 ); /* concatenates str1 and str2 */
strcat( str1, str2);
printf("strcat( str1, str2): %sn", str1 ); /* total lenghth of str1 after
concatenation */ len = strlen(str1);
printf("strlen(str1) : %dn", len );
return 0;
}
58
Output:
strcpy( str3, str1) : Hello
strcat( str1, str2):
HelloWorld strlen(str1) : 10

POINTERS, ADDRESS
ARITHMETIC
Lecture no.- 24,
UNIT- II

INTRODUCTION TO POINTERS
 Definition:
Pointers are variables that hold address of another variable
of same data type.
 Benefit of using pointers
 Pointers are more efficient in handling Array and Structure.
 Pointer allows references to function and thereby helps in
passing of function as arguments to other function.
 It reduces length and the program execution time.

It allows C to support dynamic memory management. 60

2.4.1 CONCEPT OF POINTERS
 Whenever a variable is declared, system will allocate
a location to that variable in the memory, to hold
value. This location will have its own address number.
Let us assume that system has allocated memory location 80F
for a variable a.
int a = 10 ;
61

 We can access the value 10 by either using the variable name a or
the address 80F. Since the memory addresses are simply numbers
they can be assigned to some other variable. The variable that
holds memory address are called pointer variables.
A pointer variable is therefore nothing but a variable that
contains an address, which is a location of another variable. Value
of pointer variable will be stored in another memory location.
62

 Declaring a pointer variable
 Syntax
 data-type *pointer_name;
Note:- Data type of pointer must be same as the variable,
which the pointer is pointing. void type pointer works with
all data types, but isn't used often.
 Initialization of Pointer variable
int a = 10 ;
int *ptr ; //pointer declaration
ptr = &a ; //pointer initialization or,
int *ptr = &a ; //initialization and declaration together 63

2.4.3 THE DEREFERENCING
OPERATOR
 Once a pointer has been assigned the address of a variable. To
access the value of variable, pointer is dereferenced, using
the indirection operator.
int a,*p; a = 10;
p = &a; printf("%d",*p); //this will print the value of a.
printf("%d",*&a); //this will also print the value of a.
printf("%u",&a); //this will print the address of a.
printf("%u",p); //this will also print the address of a.
printf("%u",&p); //this will also print the address of p.
64

2.4.4 ADDRESS ARITHMETIC
 A pointer in c is an address, which is a numeric value.
Therefore, we can perform arithmetic operations on a pointer
just as you can on a numeric value. There 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. 65

 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;
}
66
Output:-
Address of var[0] =
bf882b30 Value of var[0] =
10
Address of var[1] =
100
Address of var[2] =
200

 Decrementing 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[MAX-1];
for ( i = MAX; i > 0; i--)
{
printf("Address of var[%d] = %xn", i-1, ptr );
printf("Value of var[%d] = %dn", i-1, *ptr ); /* move to the previous
location */ ptr--;
}
return 0;
}
67
Output:-
Address of var[2] =
bfedbcd8
Value of var[2] = 200
Address of var[1] =
bfedbcd4
Address of var[0] =
bfedbcd0

POINTERS TO
REPRESENT ARRAY
Lecture no.- 25,
UNIT- II

2.5.1 POINTERS TO REPRESENT
ARRAYS
 we can use a pointer to point to an Array, and then we can
use that pointer to access the array.
#include <stdio.h>
const int MAX = 3;
int main ()
{
int var[] = {10, 100, 200};
int i, *ptr[MAX];
for ( i = 0; i < MAX; i++)
{
ptr[i] = &var[i]; /* assign the address of integer. */ }
for ( i = 0; i < MAX; i++)
{
printf("Value of var[%d] = %dn", i, *ptr[i] );
}
return 0;
}
69
Output:-
Value of var[1] =
100 Value of var[2]
= 200

2.5.2- POINTERS AND STRINGS
 Pointer can also be used to create strings. Pointer variables
of char type are treated as string.
Consider
The above creates a string and stores its address in the pointer
variable str. The pointer str now points to the first character
of the string "Hello".
Another important thing to note that string created
using char pointer can be assigned a value at runtime.
char *str; str = "hello"; //this is Legal
 The content of the string can be printed
using printf() and puts().
 printf("%s", str); puts(str);
Notice: That str is pointer to the string, it is also name of the
string. Therefore we do not need to use indirection operator *.
70
char *str =
"Hello";

 We can also have array of pointers. Pointers are very helpful
in handling character array with rows of varying length.
char *name[3]={"Adam“,"chris“,"Deniel”};//Now see same array
without using pointer
char name[3][20]= { "Adam", "chris", "Deniel" };
71

2.5.3 POINTERS TO POINTERS
 A pointer to a pointer is a form of multiple indirection, or a chain
of pointers. Normally, a pointer contains the address of a
variable. When we define a pointer to a pointer, the first pointer
contains the address of the second pointer, which points to the
location that contains the actual value as shown below.
 A variable that is a pointer to a pointer must be declared as such. This is
done by placing an additional asterisk in front of its name.
For example,
int **var;
72
Pointer-1
Address
Pointer-2
Address
Variable
Value

 When a target value is indirectly pointed to by a pointer to a
pointer, accessing that value requires that the asterisk
operator be applied twice, as is shown below in the example
−
#include <stdio.h>
int main ()
{
int var; int *ptr; int **pptr;
var = 3000; /* take the address of var */
ptr = &var; /* take the address of ptr using address of operator & */
pptr = &ptr; /* take the value using pptr */
printf("Value of var = %dn", var );
printf("Value available at *ptr = %dn", *ptr );
printf("Value available at **pptr = %dn", **pptr);
return 0;
}
73
Output:
Value of var = 3000
Value available at *ptr = 3000
Value available at **pptr =
3000

2.5.4 VOID POINTERS
 Definition:
The void pointer, also known as the generic pointer, is a
special type of pointer that can be pointed at objects of any data
type. A void pointer is declared like a normal pointer, using
the void keyword as the pointer's type:
void *ptr; // ptr is a void pointer
 Void Pointer Basics :
 In C General Purpose Pointer is called as void Pointer.
 It does not have any data type associated with it
 It can store address of any type of variable
 A void pointer is a C convention for a raw address.
 The compiler has no idea what type of object a void Pointer really points to ?74

 Declaration of Void Pointer :
void * pointer_name;
Void Pointer Example :
void *ptr; // ptr is declared as Void pointer
char Cnum;
int inum; float fnum;
ptr = &Cnum; // ptr has address of character data
ptr = &inum; // ptr has address of integer data
ptr = &fnum; // ptr has address of float data
75

 Explanation :
void *ptr;
1. Void pointer declaration is shown above.
2. We have declared 3 variables of integer,character and float type.
3. When we assign address of integer to the void pointer, pointer
will become Integer Pointer.
4. When we assign address of Character Data type to void pointer
it will become Character Pointer.
5. Similarly we can assign address of any data type to the void
pointer.
6. It is capable of storing address of any data type
76

 Summary : Void Pointer
77
Scenario Behavior
When We assign address of
integer variable to void
pointer
Void Pointer Becomes Integer
Pointer
character variable to void
pointer
Void Pointer Becomes
Character Pointer
floating variable to void
pointer
Void Pointer Becomes
Floating Pointer

2.6.1 COMMAND LINE ARGUMENTS
 Definition:
It is possible to pass some values from the command line to
our C programs when they are executed. These values are
called command line arguments.
The command line arguments
are handled using main() function arguments
where argc refers to the number of arguments passed,
and argv[] is a pointer array which points to each argument
passed to the program.
78

79

 Following is a simple example
#include <stdio.h>
int main( int argc, char *argv[] )
{
if( argc == 2 )
{
printf("The argument supplied is %sn", argv[1]);
}
else if( argc > 2 )
{
printf("Too many arguments supplied.n");
} else
{
printf("One argument expected.n");
}
}
80

 When the above code is compiled and executed with single
argument, it produces the following result.
$./a.out testing The argument supplied is testing
 When the above code is compiled and executed with a two
arguments, it produces the following result.
$./a.out testing1 testing2 Too many arguments supplied.
 When the above code is compiled and executed without
passing any argument, it produces the following result.
$./a.out One argument expected
NOTE: It should be noted that argv[0] holds the name of the program itself
and argv[1] is a pointer to the first command line argument supplied, and
*argv[n] is the last argument. If no arguments are supplied, argc will be one,
and if you pass one argument then argc is set at 2.
81

STRUCTURES, TYPEDEF
Lecture no.- 26,
UNIT- II

2.7.1 DECLARATION OF STRUCTURE
 Definition:-
Structure is composition of the different variables of different
data types , grouped under same name. It is user defined data
types in C.
The format of the structure statement is as follows −
struct [structure tag]
{
member definition;
member definition;
...
member definition;
} [one or more structure variables];
Note:-1. Each member declared in Structure is called member.
2. Name given to structure is called as tag
3.Structure member may be of different data type including user
defined datatype also
83

2.7.3 ACCESSING & INITIALIZATION
 Accessing Structure Members:
To access any member of a structure, we use the member
access operator (.). The member access operator is coded as a
period between the structure variable name and the structure
member that we wish to access. You would use the
keyword struct to define variables of structure type. The
following example shows how to use a structure in a program −
#include <stdio.h>
#include <string.h>
struct Books
{
char title[50];
char author[50];
char subject[100];
int book_id;
};
84

CONT…
int main( )
{
struct Books Book1; /* Declare Book1 of type Book */
struct Books Book2; /* Declare Book2 */ /* book 1 specification */
strcpy( Book1.title, "C Programming");
strcpy( Book1.author, "Nuha Ali");
strcpy( Book1.subject, "C Programming Tutorial");
Book1.book_id = 6495407; /* book 2 specification */
strcpy( Book2.title, "Telecom Billing");
strcpy( Book2.author, "Zara Ali");
strcpy( Book2.subject, "Telecom Billing Tutorial");
Book2.book_id = 6495700;
85

CONT…
/* print Book1 info */
printf( "Book 1 title : %sn", Book1.title);
printf( "Book 1 author : %sn", Book1.author);
printf( "Book 1 subject : %sn", Book1.subject);
printf( "Book 1 book_id : %dn", Book1.book_id);
/*Book2info
printf( "Book 2 title : %sn", Book2.title);
printf( "Book 2 author : %sn", Book2.author);
printf( "Book 2 subject : %sn", Book2.subject);
printf( "Book 2 book_id : %dn", Book2.book_id);
return 0;
}
86

CONT…
87
Output:
Book 1 title : C Programming
Book 1 author : Nuha Ali
Book 1 subject : C Programming Tutorial
Book 1 book_id : 6495407
Book 2 title : Telecom Billing
Book 2 author : Zara Ali
Book 2 subject : Telecom Billing Tutorial
Book 2 book_id : 6495700

2.7.4 STRUCTURE AND UNION
 Definition:
A union is a special data type available in C that allows to
store different data types in the same memory location.
We can define a union with
many members, but only one member can contain a value at
any given time. Unions provide an efficient way of using the
same memory location for multiple-purpose.
o Defining a Union
union [union tag]
{
member definition;
member definition;
...
member definition;
} [one or more Union variables];
88

#include <stdio.h>
#include <string.h>
union Data
{ int i;
float f; char str[20];
};
int main( )
{
union Data data;
data.i = 10;
data.f = 220.5;
strcpy( data.str, "C Programming");
printf( "data.i : %dn", data.i);
printf( "data.f : %fn", data.f);
printf( "data.str : %sn", data.str);
return 0;
}
89
Output:
data.i : 1917853763
data.f :4122360580327794860452759994368.000000
data.str : C Programming

2.7.5 TYPE DEFINITION
 Definition
The C programming language provides a keyword
called typedef, which we can use to give a type, a new name.
Following is an example to define a term BYTE for one-byte
numbers −
typedef unsigned char BYTE;
After this type definition, the identifier BYTE can be used
as an abbreviation for the type unsigned char, for
example.
BYTE b1, b2;
 By convention, uppercase letters are used for these
definitions to remind the user that the type name is really a
symbolic abbreviation, but we can use lowercase, as follows −
typedef unsigned char byte;
 we can use typedef to give a name to our user defined data
types as well.
90

CONT…
 For example, we can use typedef with structure to define a
new data type and then use that data type to define
structure variables directly as follows −
#include <stdio.h>
#include <string.h>
typedef struct Books
{
char title[50];
char author[50];
char subject[100];
int book_id;
} Book;
91

CONT…
int main( )
{
Book book;
strcpy( book.title, "C Programming");
strcpy( book.author, “Indrajeet");
strcpy( book.subject, "C Programming Tutorial");
book.book_id = 6495407;
printf( "Book title : %sn", book.title);
printf( "Book author : %sn", book.author);
printf( "Book subject : %sn", book.subject);
printf( "Book book_id : %dn", book.book_id);
return 0;
}
92

93
Output:
Book title : C Programming
Book author : Indrajeet
subject : C Programming Tutorial Book
book_id : 6495407

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