EST 102 Programming in C-MODULE 4

Introduction to modular programming, writing functions, formal
parameters, actual parameters .Pass by Value, Recursion, Arrays
as Function Parameters ,structure, union, Storage Classes, Scope
and life time of variables
MODULE 4
6/30/2020 NIMMY RAJU,AP,VKCET,TVM 1

Functions
• A function is a group of statements
that together perform a task.
• Every C program has at least one
function, which is main().

Why to use Functions?
• Development can be divided
• Readable programs
• Programming errors are easy to detect
• Allows re-use of codes
• Improves manageability
• Collaboration

Types of Functions
There are two types of functions in C programming:
• Standard library functions
• User-defined functions

Standard Library Functions
• The standard library functions are built-in functions
in C programming.
• These functions are defined in header files.
For example,
• The printf() is defined in the stdio.h header file.
• The sqrt() function is defined in the math.h header
file.
• The strlen() function is defined in the string.h
header file.6/30/2020 NIMMY RAJU,AP,VKCET,TVM 5

User-defined function
• User can also create functions as per their own
needs.
• Such functions created by users are known as
user-defined functions.
Advantages of user-defined function
• easier to understand, maintain and debug.
• Reusable codes
• A large program can be divided among many
programmers.

• Three parts of a user defined functions are:
– Function Declaration or Prototype
– Function Definition
– Function Call

Function Declaration or function prototype
• A function prototype or function declaration is simply
the declaration of a function that specifies function's
name, parameters and return type.
• It doesn't contain function body.
• A function prototype gives information to the compiler
that the function may later be used in the program.
Syntax
• return_type function_name( parameter list );
• int add(int a, int b);6/30/2020 NIMMY RAJU,AP,VKCET,TVM 8

Function Definition
• A function definition in C programming consists
of a function header and a function body. Here
are all the parts of a function:
Return Type:
• A function may return a value.
• The return_type is the data type of the value the
function returns.
• Some functions perform the desired operations
without returning a value.
• In this case, the return_type is the keyword void.

Function Definition
• Function Name: The actual name of the
function.
• Arguments: When a function is invoked, you
pass a value to the parameter. This value is
referred to as argument.
• Function Body: The function body contains a
collection of statements that define what the
function does.

• Syntax:
return_type function_name( argument list )
{
body of the function
}

Function Call
• When a program calls a function from the
main function , the program control is
transferred to the called function.
• A called function performs a defined task and
when its return statement is executed or
when its function-ending closing brace is
reached, it returns the program control back
to the main program.
Syntax:
• functionName(parameter list);

• Return Statement
• The return statement terminates the
execution of a function and returns a value to
the calling function.
• The program control is transferred to the
calling function after the return statement.

Types of user defined functions
Types INPUT OUTPUT
No arguments passed and
no return value
Sub function Sub function
Arguments passed but no
return value
Main function Sub function
No arguments passed but
return value
Sub function Main function
Arguments passed with
return value
Main function Main function

Without function Using function(No arguments passed and
no return value
)
#include<stdio.h>
void main()
{
int a,b,sum;
printf("Enter the values of
a & b");
scanf("%d%d",&a,&b);
sum=a+b;
printf("Sum=%d",sum);
}
#include<stdio.h>
void add();
void main()
{
add();
}
// function to read two number and
print its sum
void add()
{
int a,b,sum;
printf("Enter the values of a & b");
sum=a+b;
}
Program to find the sum of two numbers

Without function Using function(arguments passed and no
return value
)
#include<stdio.h>
void main()
{
int a,b,sum;
printf("Enter the values of a
& b");
sum=a+b;
}
#include<stdio.h>
void add(int ,int );
void main()
{
int a,b;
add(a,b);
}
// function that takes two arguments
and print their sum.
void add(int a,int b)
{
int sum= a + b;
}
Program to find the sum of two numbers

Without function Using function(No arguments passed and but
return value
)
#include<stdio.h>
void main()
{
int a,b,sum;
& b");
sum=a+b;
}
#include<stdio.h>
int add( );
void main()
{
int S;
S=add();
printf("Sum=%d",S);
}
// function to read two number and
return its sum
int add()
{
int a,b,sum;
sum = a+b;
return sum;
}6/30/2020 NIMMY RAJU,AP,VKCET,TVM 18

Without function Using function(arguments passed with return
value
)
#include<stdio.h>
void main()
{
int a,b,sum;
& b");
sum=a+b;
}
#include<stdio.h>
int add(int ,int );
void main()
{
int a,b,S;
S=add(a,b);
printf("Sum=%d",S);
}
// function that takes two arguments
and print their sum.
int add(int a,int b)
{
int sum;
sum = a+b;
return sum;
}

No arguments
passed and no
return value
No arguments
passed and no return
value
No arguments passed
and no return value
No arguments passed
and no return value
#include<stdio.h>
void large();
void main()
{
large();
}
void large()
{
int a,b;
printf("Enter the
values of a & b");
scanf("%d%d",&a,&b)
;
If(a>b)
printf(“Largest=%d",a
);
else
printf(“Largest=%d“,a
);
}
#include<stdio.h>
void large(int,int);
void main()
{
int a,b;
printf("Enter the values
of a & b");
large(a,b);
}
void large(int x,int y)
{
If(x>y)
printf(“Largest=%d",x);
else
printf(“Largest=%d“,y);
}
#include<stdio.h>
int large();
void main()
{
int l;
l=large();
printf(“Large=%d”,l);
}
int large()
{
int a,b;
printf("Enter the values of
a & b");
If(a>b)
return a;
else
return b;
}
#include<stdio.h>
int large(int,int);
void main()
{
int a,b,l;
printf("Enter the values
of a & b");
l=large(a,b);
printf(“Large=%d”,l);
int large(int a,int b)
{
If(a>b)
return a;
else
return b;
}
Largest of two numbers

• Formal and Actual Parameters
• Let us assume that a function B() is called
from another function A().
• In this case A is called the “caller functionor
calling function” and B is called the “called
function or callee function”.
• Also, the arguments which A sends to B are
called actual arguments and the parameters
of B are called formal arguments.

• Formal Parameter: A variable and its type as
they appear in the prototype of the function
or method.
• Actual Parameter: The variable or expression
corresponding to a formal parameter that
appears in the function or method call in the
calling environment.

Formal and Actual parameters
 Let us assume that a function B() is called from another function
A(). In this case A is called the “caller function or calling
function” and B is called the “called function or callee
function”.
 The arguments which A sends to B are called actual arguments
(parameters)and the arguments of B are called formal
arguments(parameters).
 Formal Parameter: A variable that appears in the prototype of
the function.
 Actual Parameter: The variable corresponding to a formal
parameter that appears in the function call in the calling function.

Example:
#include<stdio.h>
int swap(int a,int b); //function declaration
void main()
{
int x=10,y=20;
printf("Before swapping : x=%dty=%dn",x,y);
swap(x,y); //function call
printf("After swapping : x=%dty=%d",x,y);
}
int swap(int a,int b) //function definition
{
int temp=a;
a=b;
b=temp;
printf("a=%dt b=%d",a,b);
}
Output
Before swapping: x=10 y=20
a=20 b=10
After swapping : x=10 y=20

Pass by value(Call by value)
• In this parameter passing technique, a copy of
actual parameter is passed to formal parameter.
• As a result, any changes or modification
happened to formal parameter won’t reflect
back to actual parameter

Example:
#include<stdio.h>
int swap(int a,int b); //function declaration
void main()
{
int x=10,y=20;
swap(x,y); //function call –pass by value
}
int swap(int a,int b) //function definition
{
int temp=a;
a=b;
b=temp;
printf("a=%dt b=%d",a,b);
}
Output
a=20 b=10

Pass by reference(Call by reference)
• Both the actual and formal parameters refer to
same locations, so any changes made inside
the function are actually reflected in actual
parameters of caller.

Example:
#include<stdio.h>
int swap(int *a,int *b); //function declaration
void main()
{
int x=10,y=20;
swap(&x,&y); //function call –pass by reference
}
int swap(int *a,int *b) //function definition
{
int temp=*a;
*a=*b;
*b=temp;
printf("a=%dt b=%d",*a,*b);
}
Output
a=20 b=10

Recursive Function
• A function that calls itself is known as a
recursive function. And, this technique is known as
recursion.
• While using recursion, programmers need to be
careful to define an exit condition from the
function, otherwise it will go into an infinite loop.
• Recursion makes program elegant.

Write a program to find factorial of number using recursive function
#include<stdio.h>
int fact(int n)
{
if( n == 0)
return 1;
return n*fact(n-1);
}
void main()
{
int n,f;
printf("Enter the number:");
scanf("%d",&n);
f-=fact(n);
printf("factorial=%d",f);
}
Output
Enter the number:5
factorial=120
fact(5) fact(4) fact(3) fact(2) fact(1) fact(0)
fact(5)
{
return
5*fact(4);
}
fact(4)
{
return
4*fact(3);
}
fact(3)
{
return
3*fact(2);
}
fact(2)
{
return
2*fact(1);
}
fact(1)
{
return
1*fact(0);
}
fact(0)
{
return 1;
}
5*24=120 4*6=24 3*2=6 2*1=2 1*1=1 1

Write a program to find sum of first n natural numbers using recursive function
#include<stdio.h>
int sum(int n)
{
if( n == 0)
return 0;
return n+sum(n-1);
}
void main()
{
int n,f;
printf("Enter the limit:");
scanf("%d",&n);
printf(“n Sum=%d",sum(n));
}
Output
Enter the limit:5
factorial=15
sum(5) sum(4) sum(3) sum(2) sum(1) sum(0)
sum(5)
{
return
5+sum(4);
}
sum(4)
{
return
4+sum(3);
}
sum(3)
{
return
3+sum(2);
}
sum(2)
{
return
2+sum(1);
}
sum(1)
{
return
1+sum(0);
}
sum(0)
{
return 0;
}
5+10=15 4+6=10 3+3=6 2+1=3 1+0=1 0

Passing an array as Parameter
 Like the value of simple variables, it is also
possible to pass the values of an array to a
function.
 To pass a single dimensional array to a
function, it is sufficient to list the name of the
array without any subscripts and the size of
the array as arguments

Rules to pass an Array to Function
 The function must be called by passing only the
name of the array.
 In function definition, formal parameter must be
an array type; the size of the array does not need
to be specified.
 The function prototype must show that the
argument is an array.

Write a function to sort an array.
#include<stdio.h>
int sort(int A[],int n)
{
int i,j,temp;
for(i=0;i<n-1;i++)
{
for(j=0;j<n-i-1;j++)
{
if(A[j]>A[j+1])
{
temp = A[j];
A[j] = A[j+1];
A[j+1]= temp;
}
}
}
void main()
{
int A[30],i,n;
printf("Enter the limit:");
scanf("%d",&n);
for(i=0;i<n;i++)
{
printf("Enter the
element:");
scanf("%d",&A[i]);
}
sort(A,n);
printf("Sorted Arrayn");
for(i=0;i<n;i++)
printf("%dt",A[i]);
}
Output
Enter the limit:5
Enter the element:17
Enter the element:23
Enter the element:5
Enter the element:2
Enter the element:9
Sorted Array
2 5 9
17 23

• Passing 2 D array as parameter
• While passing 2D as parameter we need to
mention the max size of element of each row
that is column

Write a program to pass a 2 D matrix as parameter and find its sum of all the elements
#include<stdio.h>
// function that takes a 2 D
and its order
int sum(int A[][30],int m,int
n)
{
int i,j,sum =0;
for(i=0;i<m;i++)
{
for(j=0;j<n;j++)
{
sum = sum + A[i][j];
}
}
}
} void main()
{
int A[30][30];
int i,n,m,j;
printf("Enter the order of
matrix:");
scanf("%d%d",&m,&n);
for(i=0;i<m;i++)
{
for(j=0;j<n;j++)
{
printf("Enter the element:");
scanf("%d",&A[i][j]);
}
}
sum(A,m,n);
}
Output
Enter the order of
matrix:2 2
Enter the element:1
Enter the element:2
Enter the element:3
Enter the element:4
Sum=10

STRUCTURE
• A structure is a user defined data type in C.
• A structure creates a data type that can be
used to group items of possibly different types
into a single type.
• ‘struct’ keyword is used to create a structure.

• Consider we want to create the structure of a
person with following variable name, age and
address.
• Then such a structure can be created as
struct Person
{
char name[30];
int age;
char addr[50];
}p;

The general format of a structure definition is as
follows
struct structure_name
{
data_type member1;
data_type member2;
---------------------
---------------------
}S;
Here S is called structure variable.6/30/2020 NIMMY RAJU,AP,VKCET,TVM 39

• A structure variable can either be declared
with structure declaration or as a separate
declaration like basic types.
{
data_type member1;
data_type member2;
---------------------
---------------------
}:
void main()
{
struct structure_name S;
}
{
data_type member1;
data_type member2;
---------------------
---------------------
}S;

Declare a structure namely Student to store the details (roll number,
name, mark_for_C) of two students and display the data.
#include<stdio.h>
struct Student
{
char name[30];
int rollnum;
int mark;
};
void main()
{
struct Student s1,s2;
printf("Enter the Student name:");
scanf("%s",s1.name);
printf("Enter the Student rollnum:");
scanf("%d",&s1.rollnum);
printf("Enter the Student Mark for C:");
scanf("%d",&s1.mark);
printf("NametRoll NumbertMark for Cn");
printf("%st%dt%dn",s1.name,s1.rollnum,s1.m
ark);
ark);
}
Output
Enter the Student name:Sangeeth
Enter the Student rollnum:
Enter the Student Mark for C:35
Enter the Student name:Pratheesh
Enter the Student rollnum:24
Name Roll Number Mark for C
Sangeeth 27 35
Pratheesh 24 40

Array of Structures
 DeclareastructurenamelyStudenttostorethedetails(roll number, name, mark_for_C)
of a student. Then, write a program in C to find the average mark obtained by the
students in a class for the subject Programming in C (using the field mark_for_C). Use
array of structures to store the required data.

Declare a structure namely Student to store the details (roll number,
name, mark_for_C) of two students and display the data.
#include<stdio.h>
struct Student
{
char name[30];
int rollnum;
int mark;
};
void main()
{
struct Student s1,s2;
printf("NametRoll NumbertMark for Cn");
ark);
ark);
}
Output
Enter the Student rollnum:
Sangeeth 27 35
Pratheesh 24 40

#include<stdio.h>
struct Student
{
char name[30];
int rollno;
int mark_for_C;
};
void main()
{
struct Student s[30];
int i,n,sum=0;
float avg;
printf("Enter the no
of Student:");
scanf("%d",&n);
for(i=0;i<n;i++)
{
printf("Enter the Student
name:");
scanf("%s",s[i].name);
printf("Enter the Student
rollno:");
scanf("%d",&s[i].rollno);
printf("Enter the Mark for C:");
scanf("%d",&s[i].mark_for_C);
}
printf("NametRoll
NumbertMark for Cn");
for(i=0;i<n;i++)
{
printf("%st%dt%dn",s[i].name,
s[i].rollnum,s[i].mark_for_C);
sum = sum + s[i].mark_for_C;
}
avg = (float)sum /n;
printf("Average Mark=%fn",avg);
}

Output
Enter the no of Student:3
Enter the Student name:Poornima
Sangeeth 27 35
Pratheesh 24 40
Poornima 26 45
Average Mark=40.00

UNION
 A union is a user-defined type similar to struct in C
programming.
 We use the union keyword to define unions.
Example of Employee Union creation and declartion
union Employee
{
char name[30]; int age;
double salary;
};
union Employee e;

Difference between structure and union
Structure Union
struct keyword is used to define a structure union keyword is used to define a union
Members do not share memory in a structure. Members share the memory space in a union
Any member can be retrieved at any time in a
structure
Only one member can be accessed at a time
in a union.
Several members of a structure can be
initialized at once.
Only the first member can be initialized.
Sizeofthestructureisequalto thesumofsize
of the each member.
Size of the union is equal to the size of the
largest member.

#include<stdio.h>
struct Person
{
char pincode[6]; // Size = 6 bytes
int age; // Size = 4 bytes
double salary;// Size = 8 bytes
};
union Employee
{
char pincode[6];
int age;
double salary;
};
void main()
{
struct Person p;
union Employee e;
printf("Size of Structure Person=%dn",sizeof(p));
printf("Size of Union Employee=%d",sizeof(e));
}
Output
Size of Structure Person=18
Size of Union Employee=86/30/2020 NIMMY RAJU,AP,VKCET,TVM 48

Storage Classes, Scope and life
time of variables

• In C, not only do all the variables have a data
type, they also have a storage class.
• The following variable storage classes are
most relevant to functions
– Automatic Variables
– External or Global Variables
– Static Variables
– Register Variables

Automatic Variables
• Automatic variables are declared inside a
function in which they are to be utilized.
• They are created when the function is called
and destroyed automatically when the
function is exited, hence the name automatic.
• Automatic variables are therefore private or
local to the function in which they are
declared.
• Because of this property, automatic variables
are also referred to as local or internal
variables.

Automatic Variables
• A variable declared inside a function without
storage class specification is by default an
automatic variable.
void main()
{
int num;
}
is same as
void main()
{
auto int num;
}

• Example
#include<stdio.h>
void func1()
{
int max=10;
printf("Max in func1()=%dn",max);
}
void func2()
{
int max=20;
}
void main()
{
int max=30;
func1();
func2();
printf("Max in main()=%dn",max);
}
Output
Max in func1()=10
Max in func2()=20
Max in main()=30

External Variables
• Variables that are both alive and active
throughout the entire program are known as
external variables.
• They are called global variables.
• Unlike local variables, global variables can be
accessed by any function in the program.
• External global variables are global variables
visible to all file other than in which it is
declared6/30/2020 NIMMY RAJU,AP,VKCET,TVM 54

#include<stdio.h>
int max;
void func1()
{
}
void func2()
{
}
void main()
{
max=30;
func1();
func2();
printf("Max in main()=%dn",max);
}
Max in func1()=30
Max in func1()=30
Max in main()=30

Static Variables
• As the name suggests, the value of static
variables persists until the end of the
program.
• A variable can be declared static using the
keyword static like
static int x;
• Static global variables are global variables
visible only to the file in which it is declared.

Register Variables
• We can tell the compiler that a variable should be
kept in one of the machine’s registers instead of
keeping in the memory.
• Since a register access is fast than a memory
access, keep in the frequently accessed variables
in the register will lead to faster execution of
programs.
• This is done as follows
register int count;

• The scope of a variable is the part of the
program within which the variable can be
used. So, the scope describes the visibility of
an identifier within the program.
• The lifetime of a variable or function is the
time duration for which memory is allocated
to store it, and when that memory is released.

StorageClass Wheredeclared Visibility Lifetime
extern
Beforeallfunctionsinafile
Entire file plus other
files where variable is
declared.
Global
Static
Beforeallthefunctioninafile Onlyinthatfile
Global
Noneorauto
Inside afunction
Only in that function
orblock
Until end of
function
Register
Inside afunctionorblock
Onlyinthatfunction
orblock
Until end of
function

EST 102 Programming in C-MODULE 4

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