manish k parmar pgt (cs) k v vvnagar thursday, december 24, 2015 lesson on user defined function in...

Manish K ParmarPGT (CS)

K V VVNagar

Friday, April 21, 2023

Lesson on

USER DEFINED FUNCTION IN C++

Presented by

Manish K Parmar

PGT Computer Science

Kendriya Vidyalaya VVNagar


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USE DEFINED FUNCTIONS

C++


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FUNCTIONS

A Function groups a number of program statements into a single unit and gives it a name. It takes arguments and returns a value.

This unit can be called (invoked) from other parts of the program. Functions are the building blocks of C++ programs where all the program activity occurs.

Functions serve two purposes. They allow a programmer to say: `this piece of code does a specific job which stands by itself and should not be mixed up with anyting else', and they make a block of code reusable since a function can be reused in many different contexts without repeating parts of the program text.


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Need for a Function

Monolethic program (a large single list of instructions) becomes difficult to understand. For this reason functions are used.

A Function has a clearly-defined objective (purpose) and a clearly-defined interface with other functions in the program.

A group of functions together is called a module.

Reduction in program size is the another reason. Any sequences of statements that is repeated in a program can be combined together to form a function. The function code has only one copy in memory, even though it may be executed as many times as a user needs.


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Advantages of using functions in C++

A complex program can be divided into small subtasks and function subprograms can be written for each.

These are easy to write, understand and debug

A function can be utilized in many programs by separately compiling it and loading them together.

C++ has the facility of defining a function in terms of itself i.e. recursion.

Many functions such as cin, cout, sqrt etc. are kept in C++ library and the compiler of C++ is written for calling any such function.


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Types of Functions

1. Library Functions / Built in Functions

Many functions are in built with C++ language by default. They are library functions and stored in the header files of C++.

Eg. pow(), getch(), exit(), etc.

2. User Defined Functions

User can create a new functions as per his/her requirement


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Function Prototype

Like any variable in a C++ program it is necessary to prototype or declare a function before it’s use.

It informs the compiler that the function would be referenced at a later stage in the program.

Eg.void display_message();

is a function prototype or a declaration. Here void specifies that this function does not return any value.


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Defining a Function

A Function must be defined prior to it’s use in the program. It contains the code of the function.

Syntax of a function definition :

Type Name_of_the_function (argument list)

{

// body of the function

}


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Defining a Function

Example :

int Sum (int a, int b)

{

int c;

c = a + b;

return c;

}


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Function Call / Invoke a Function

A Function can be used by calling it or invoking it in the main program.

Eg.

Total = sum(5, 9);


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Example of A Function

#include<iostream.h>

int Cube(int);

void main()

{

int number, cube;

cout << “\n Enter No :”;

cin >> number;

cube = Cube(number);

cout << “\n Cube of the no is : “ << cube;

}

Int Cube(int n)

{

return n * n * n;

}


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Arguments

The inputs which are given to the functions are known as Function Arguments.

Constant Arguments

Default Arguments


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Arguments

Constant Arguments

void max (const float x, const float y);

Here, the qualifier const informs the compiler that the arguments having const should not be modified by the function max().


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Arguments

Default Arguments

C++ allows a function to assign a parameter the default value in case no argument for that parameter is specified in the function call.

void pattern (char M, int B = 2);

to print the character M for B times.

if pattern(‘@’, 4) then it prints @ four times.

if pattern(‘*’) then it printe * two times.


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Calling Functions

Function can be called by two ways.

1. Call by Value

2. Call by Reference


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Call by Value

Here the function is called by the value of arguments. Here two words are used Actual Parameter and Formal Parameter.

The parameter passed in function call is known as Actual Parameter, while the parameter declared in the definition is called as Formal Parameter.


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Call by Value


int Sum(int, int);

void main()

{

int n1, n2, Total;

cout << “\n Enter No 1 :”; cin >> n1;


Total = Sum(n1, n2); // n1, n2 : Actual Parameters

cout << “\n Total : “ << Total;

}

int Sum (int a, int b) // a, b : Formal Parameters

{

return a + b;

}


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Call by Reference

A reference provides an alias – a different name – for the variable, that is, the same variable’s value can be used by two different names : the original name and the alias name.

In call by reference method, a reference to the actual arguments in the calling program is passed (only variables). So the called function does not create its own copy of original value(s) but works with the original values with different name.


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Call by Reference


void main()

{

int n1, n2, Total;

int Sum(int &a, int &b);



Total = Sum(n1, n2);


}

int Sum (int &a, int &b)

{

return a + b;

}


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How control passed between functions


int Sum(int, int);

void main()

{

int n1, n2, Total;

cout << “\n Enter No 1 :”;

cin >> n1;

cout << “\n Enter No 2 :”;

cin >> n2;

Total = Sum(n1, n2);


}

int Sum (int a, int b)

{

return a + b;

}


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Returning from Function…

Return Statement is used to return a value from function.int fun(){………return <variable> or <value>;}

A function can return only a single value.

There may be three types of functions :

Computational Functions : Calculate some value and return it.

Manipulative Functions : Manipulate information and return success or failure code.

Procedural Functions : Perform an action and have no explicit return value.


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Returning (by) Reference

A fuction may also return a reference.

int & min (int & a, int & b){

if (a < b)return a;

elsereturn b;

}

This function returns reference to a or b rather than returning values.

For eg. min (x, y) = -5;

It assigns -5 to lesser of the two x and y.


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Function Classification…

Function can be classified into four categories as per the arguments and return values.

1. No Arguments and No Return Values

2. No Arguments but Return Values

3. Arguments but No Return Values

4. Arguments and Return Values


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No Arguments No Return Values


void print_name();

void main()

{

print_name();

}

void print_name()

{

cout << “\n Sachin Tendulkar”;

}


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No Arguments But Return Values


int get_number();

void main()

{

int n;

n = get_number();

}

int get_number()

{

int a;

cout << “\n Enter No : ”; cin >> a;

return a;

}


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Arguments but No Return Values


void print_name(int);

void main()

{

print_name(10);

}

void print_name(int n)

{

for (int i= 1; i<=n; i++)

cout << “\n Sachin Tendulkar”;

}


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Both Arguments and Return Values


int Sum(int, int);

void main()

{

int n1, n2, Total;



Total = Sum(n1, n2); // n1, n2 : Actual Parameters


}

int Sum (int a, int b) // a, b : Formal Parameters

{

return a + b;

}


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Scope Rules

The program part (s) in which a particular piece of

code or a data value (variable) can be accessed is

known as the piece-of-code’s or variable’s scope.

Four kinds of Scope in C++ :

(i) Local Scope (Block)

(ii) Function Scope

(iii) File Scope

(iv) Class Scope


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Scope of Variable


int global_var; // Global Variable

void main()

{

int local_var; // Local Variable/Fun Scope

cout << ::global_var; // :: - scope resolution operator

{

char Block_var; // Block Variable

…

}

}

void fun()

{

float fun_var; // Function Scope

}


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Example of Scope

Find out the output of the following code :


int a = 20;

void main()

{

int a = 50;

cout << ::a << “\n” << a;

}


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Example of Scope

Find out the output of the following code :


int a = 20;

void main()

{

int a = 50;

cout << ::a << “\n” << a;

}

Output :

20

50


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Example of ScopeFind out the Output for the following :

#include<iostream.h>#include<conio.h>int g=10;void func(int &x, int y){

x = x - y;y = x *10;cout<<x<<“ – “<<y<<endl;

}void main( ){

int g=7;func(::g, g);cout<<g<<“ – “<<::g<<endl;func(g, ::g);cout<<g<<“ – “<<::g<<endl;

}


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Example of ScopeFind out the Output for the following :

#include<iostream.h>#include<conio.h>int g=10;void func(int &x, int y){

x = x - y;y = x *10;cout<<x<<“ –

“<<y<<endl;}void main( ){

int g=7;func(::g, g);cout<<g<<“ –

“<<::g<<endl;func(g, ::g);cout<<g<<“ –

“<<::g<<endl;}

OUTPUT

3 – 307 – 34 – 404 – 3


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Lifetime of a variable

The time interval for which a particular variable or data

value lives in the memory is called Lifetime of the

variable or data value.

Generally a variable’s life time is its parent-block-run i.e.

as long as its parent block is executing, the variable

lives in the memory.

The global variable’s life time is the program-run.

The life time of local variable having function scope is

the function-run.


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Thank You…

manish k parmar pgt (cs) k v vvnagar thursday, december 24, 2015 lesson on user defined function in...

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