Unit iv functions

FUNCTIONS
UNIT- IV
Fundamental of Computer
programming -206

By- Er. Indrajeet Sinha , +919509010997
CONTENTS: UNIT-IV
 Functions in C
 Passing Parameters, using returned data
 Passing arrays, passing characters and strings
 Passing structures, array of structures, pointer to structure
 The void pointer,
2

FUNCTIONS IN C
Lecture no.- 34,
UNIT- IV

4.1.1- INTRODUCTION TO MODULAR
PROGRAMMING
 Definition
A modular programming is the process of subdividing a
computer program into separate sub-programs.
 The benefits of using modular programming include:
 Less code has to be written.
 A single procedure can be developed for reuse,
eliminating the need to retype the code many times.
 Programs can be designed more easily because a small
team deals with only a small part of the entire code.
 Modular programming allows many programmers to
collaborate on the same application.
 The code is stored across multiple files.
 Code is short, simple and easy to understand.
4

4.1.2- FUNCTION DECLARATION,
CALLING AND DEFINITION
 Definition:-
A function is a group of statements that together perform a
task. Every C program has at least one function, which
is main(), and all the most trivial programs can define
additional functions.
 Defining a Function
The general form of a function definition in C programming
language is as follows −
return_type function_name( parameter list )
{
body of the function ;
}
5

CONT…
 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 Name − This is the actual name of the function. The
function name and the parameter list together constitute the
function signature.
 Parameters − A parameter is like a placeholder. When a
function is invoked, you pass a value to the parameter. This value
is referred to as actual parameter or argument. The parameter
list refers to the type, order, and number of the parameters of a
function. Parameters are optional; that is, a function may contain
no parameters.
 Function Body − The function body contains a collection of
statements that define what the function does.
6

 Example:
/* function returning the max between two numbers */
int max(int num1, int num2)
{ /* local variable declaration */
int result;
if (num1 > num2) result = num1;
else result = num2;
return result;
}
7

 Function Declarations
A function declaration tells the compiler about a function name
and how to call the function. The actual body of the function can
be defined separately.
A function declaration has the following parts − return_type
function_name( parameter list );
int max(int num1, int num2);
Parameter names are not important in function declaration only
their type is required, so the following is also a valid declaration
int max(int, int);
8

 Calling a Function
 While creating a C function, we give a definition of what the
function has to do. To use a function, we will have to call that
function to perform the defined task.
 When a program calls a 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.
 To call a function, we simply need to pass the required
parameters along with the function name, and if the function
returns a value, then we can store the returned value.
9

For example −
#include <stdio.h>
int max(int num1, int num2); /* function declaration */
int main ()
{ /* local variable definition */
int a = 100;
int b = 200;
int ret;
ret = max(a, b); /* calling a function to get max value */
printf( "Max value is : %dn", ret );
return 0;
} /* function returning the max between two numbers */
int max(int num1, int num2)
{ /* local variable declaration */
int result;
if (num1 > num2) result = num1;
else result = num2;
return result;
}
10

4.1.3 & -1.4 STANDARD LIBRARY &
USER DEFINE FUNCTIONS
C functions can be classified into two categories:-
 Library functions
 User-defined functions
11

 Definition:
 Library functions are those functions which are defined
by C library, example printf(), scanf(), strcat() etc. we
just need to include appropriate header files to use these
functions. These are already declared and defined in C
libraries.
 User-defined functions are those functions which are
defined by the user at the time of writing program.
Functions are made for code reusability and for saving
time and space.
12

PASSING PARAMETERS,
USING RETURNED DATA
Lecture no.- 35,
UNIT- IV

4.2.1 PARAMETER PASSING
MECHANISM
Definition:
What is Parameter ?
In computer programming, a parameter is a special kind of
variable, used in a subroutine to refer to one of the pieces of
data provided as input to the subroutine.These pieces of data
are called arguments.
Function With Parameter :
add(a,b);
Here Function add() is Called and 2 Parameters are Passed to
Function. a,b are two Parameters.
Function Call Without Passing Parameter :
Display();
14

15
PARAMETERS
Example:
Formal parameters
float ave(float a, float b) { return (a+b)/2.0; }
Actual parameters
ave(x, 10.0)

4.2.1.1- BY VALUE
Function Arguments
While calling a function, there are two ways in which
arguments can be passed to a function −
1. Call by value
2. Call by reference
The call by value method of passing arguments to a
function copies the actual value of an argument into the
formal parameter of the function. In this case, changes made
to the parameter inside the function have no effect on the
argument.
16

 Example:
Consider the function swap()definition as follows.
/* function definition to swap the values */
void swap(int x, int y)
{
int temp;
temp = x; /* save the value of x */
x = y; /* put y into x */
y = temp; /* put temp into y */
return;
}
17

let us call the function swap() by passing actual values as in the
following example −
#include <stdio.h> /* function declaration */
void swap(int x, int y);
int main ()
int a = 100;
int b = 200;
printf("Before swap, value of a : %dn", a );
printf("Before swap, value of b : %dn", b );
/* calling a function to swap the values */
swap(a, b);
printf("After swap, value of a : %dn", a );
printf("After swap, value of b : %dn", b );
return 0;
} 18
Output:-
Before swap, value of a :100
Before swap, value of b :200
After swap, value of a :100
After swap, value of b :200
Note:-It shows that there are no changes in the values, though they
had been changed inside the function.

4.2.1.2 BY REFERENCE
The call by reference method of passing arguments to a
function copies the address of an argument into the formal
parameter. Inside the function, the address is used to access
the actual argument used in the call. It means the changes
made to the parameter affect the passed argument.
Example:
/* function definition to swap the values */
void swap(int *x, int *y)
{
int temp; temp = *x; /* save the value at address x */
*x = *y; /* put y into x */
*y = temp; /* put temp into y */
return;
}
19

void swap(int *x, int *y);
int main ()
int a = 100;
int b = 200;
printf("Before swap, value of a : %dn", a );
printf("Before swap, value of b : %dn", b );
/* calling a function to swap the values. * &a indicates pointer to a ie.
address of variable a and * &b indicates pointer to b ie. address of
variable b. */
swap(&a, &b);
printf("After swap, value of a : %dn", a );
printf("After swap, value of b : %dn", b );
return 0;
}
20
Note:-It shows that the change has reflected outside the function as well, unlike
call by value where the changes do not reflect outside the function.
Output:-
Before swap, value of a :100
Before swap, value of b :200
After swap, value of a :100
After swap, value of b :200

PASSING ARRAYS, PASSING
CHARACTERS AND
STRINGS
Lecture no.- 36,
UNIT- IV

4.3.1 PASSING ARRAY TO A
FUNCTION
 Whenever we need to pass a list of elements as argument to
the function, it is prefered to do so using an array.
 Declaring Function with array in parameter list
22

EXAMPLE PASSING ARRAY
Function:
double getAverage(int arr[], int size)
{
int i; double avg;
double sum = 0;
for (i = 0; i < size; ++i)
{
sum += arr[i];
}
avg = sum / size;
return avg;
}
23

 Now, let us call the above function as follows −
double getAverage(int arr[], int size);
int main ()
{ /* an int array with 5 elements */
int balance[5] = {1000, 2, 3, 17, 50};
double avg;
/* pass pointer to the array as an argument */
avg = getAverage( balance, 5 ) ;
/* output the returned value */
printf( "Average value is: %f ", avg );
return 0;
} 24
Output:-
Average value is: 214.400000

4.3.3 PASSING STRINGS TO
FUNCTION Strings are just char arrays. So, they can be passed to a function
in a similar manner as arrays.
#include <stdio.h>
void displayString(char str[]);
int main()
{
char str[50];
printf("Enter string: ");
gets(str);
displayString(str); // Passing string c to function.
return 0;
}
void displayString(char str[])
{
printf("String Output: ");
puts(str);
}
25

4.3.4 PASSING POINTERS TO A
FUNCTION C programming allows passing a pointer to a function. To do
so, simply declare the function parameter as a pointer type.
#include <stdio.h>
#include <time.h>
void getSeconds(unsigned long *par);
int main ()
{
unsigned long sec; getSeconds( &sec );
/* print the actual value */
printf("Number of seconds: %ldn", sec );
return 0;
}
void getSeconds(unsigned long *par)
{ /* get the current number of seconds */
*par = time( NULL );
return;
}
26
Output:-
Number of seconds :1294450468

PASSING STRUCTURES, ARRAY OF
STRUCTURES, POINTER TO
STRUCTURES, THE VOID POINTER
Lecture no.- 37,
UNIT- IV

4.4.1 PASSING STRUCTURE TO
FUNCTION
 In C, structure can be passed to functions by two methods:
 Passing by value (passing actual value as argument)
 Passing by reference (passing address of an argument)
 Passing structure by value
 A structure variable can be passed to the function as an
argument as a normal variable.
 If structure is passed by value, changes made to the structure
variable inside the function definition does not reflect in the
originally passed structure variable.
28

 C program to create a structure student, containing name and
roll and display the information.
29
#include <stdio.h>
struct student
{
char name[50];
int roll;
};
void display(struct student stu); //
function prototype should be below to
the structure declaration otherwise
compiler shows error
int main()
{
struct student stud;
printf("Enter student's name: ");
scanf("%s", &stud.name);
printf("Enter roll number:");
scanf("%d", &stud.roll);
display(stud); // passing structure
variable stud as argument
return 0;
}
void display(struct student stu)
{
printf("OutputnName:
%s",stu.name);
printf("nRoll: %d",stu.roll);
}
Output:
Enter student's name: Kevin
Amla
Enter roll number: 149
Output
Name: Kevin Amla
Roll: 149

 Passing structure by reference
• The memory address of a structure variable is passed to
function while passing it by reference.
• If structure is passed by reference, changes made to the
structure variable inside function definition reflects in the
originally passed structure variable.
 C program to add two distances (feet-inch system)
and display the result without the return
statement.
30

#include <stdio.h>
struct distance
{
int feet; float inch;
};
void add(struct distance d1,struct
distance d2, struct distance *d3);
int main()
{
struct distance dist1, dist2, dist3;
printf("First distancen");
printf("Enter feet: ");
scanf("%d", &dist1.feet);
printf("Enter inch: ");
scanf("%f", &dist1.inch);
printf("Second distancen");
printf("Enter feet: ");
scanf("%d", &dist2.feet);
printf("Enter inch: ");
scanf("%f", &dist2.inch);
add(dist1, dist2, &dist3);
//passing structure variables dist1
and dist2 by value whereas
passing structure variable dist3 by
reference
printf("nSum of distances =
%d'-%.1f"", dist3.feet,
dist3.inch);
return 0;
}
….
…..
Cont… in next slide
31

 #include <stdio.h>
 struct distance
 {
 int feet; float inch;
 };
 void add(struct distance d1,struct distance d2,
struct distance *d3);
 int main()
 {
 struct distance dist1, dist2, dist3;
 printf("First distancen");
 printf("Enter feet: ");
32

void add(struct distance d1,struct distance d2, struct distance
*d3)
{
//Adding distances d1 and d2 and storing it in d3
d3->feet = d1.feet + d2.feet; d3->inch = d1.inch + d2.inch;
if (d3->inch >= 12)
{
/* if inch is greater or equal to 12, converting it to feet. */
d3->inch -= 12; ++d3->feet;
}
}
Output
First distance Enter feet: 12
Enter inch: 6.8
Second distance Enter feet: 5
Enter inch: 7.5
33

 In this program, structure variables dist1 and dist2 are passed
by value to the add function (because value
of dist1 and dist2 does not need to be displayed in main
function).
 But, dist3 is passed by reference ,i.e, address of dist3 (&dist3) is
passed as an argument.
 Due to this, the structure pointer variable d3 inside
the add function points to the address of dist3 from the
calling main function. So, any change made to the d3 variable is
seen in dist3 variable in main function.
34

4.4.4- VOID POINTER
 Void Pointers in C : Definition
 Suppose we have to declare integer pointer, character pointer
and float pointer then we need to declare 3 pointer variables.
 Instead of declaring different types of pointer variable it is
feasible to declare single pointer variable which can act as
integer pointer, character 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 ?
35

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 36

Explanation :
void *ptr;
Void pointer declaration is shown above.
We have declared 3 variables of integer, character and float type.
1. When we assign address of integer to the void pointer,
pointer will become Integer Pointer.
2. When we assign address of Character Data type to void
pointer it will become Character Pointer.
3. Similarly we can assign address of any data type to the
void pointer.
4. It is capable of storing address of any data type 37

 Summary : Void Pointer
38
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

COMPUTER, NUMBER SYSTEM
UNIT- V
Fundamental of Computer
programming -206

Unit iv functions

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