Function lecture

transcript

A Lecture

on Function in C

Prepared by: AJAY KUMAR Assistant Professor Department of CSE DIT University, Dehradun

Introduction to Function in C

• Rely on person for so many other things

Eg. call a mechanic to fix up your bike

hire a gardener to mow your lawn

rely on a store to supply you groceries every month

• Similarly a computer program cannot handle all the tasks by itself.

• So it requests other program —called ‘functions’ in C—to get its tasks done.

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Modular Programming (Top-Down Programming)

• Large program is broken into segments i.e.number of smaller and simpler tasks. • All individual segment is known as “module”.

Eg. In a mobile phone, contact list SMS calculator games so on…

Module

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Advantage of Modular Programming

• Codes and variables are isolated from other program

• Easy to debug or trace the errors

• Reuse the same code in other program also

• Less effort to write a new code for similar task

eg. printf(), scanf(), clrscr(),sqrt()

Function

• A function is a self-contained block of statements that perform a coherent task of some kind.

• A function that calls or activates the function and the function itself.

F U N C T I O N

SYSTEM-DEFINED FUNCTION Or PRE-DEFINED function

Or Library function Or Built-in Function

User-Defined Function

Basic structure of function

Return_type function_name (arguments_list) { set of statements (or function body) }

Function (contd…)

• Built-in Function

Eg. Sqrt(),pow(),printf(),scanf()

• User-defined Function’s components

– Return type

– Function name

– Function argument list

– Function’s body= set of statements

Function categories on the basis of argument_list and return_type

• 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 return values

First Program of Function #include<stdio.h> #include<conio.h> void main() { clrscr(); printf(“\n hello ”); message(); printf(“\n everyone”); getch(); } // function start message() { printf(“\n good morning”); }

Output: Hello Good morning everyone

First program of Function

#include<stdio.h> #include<conio.h> void main() { clrscr(); printf(“\n hello ”); message(); printf(“\n everyone”); getch(); } // function start message() { printf(“\n good morning”); }

Header File

Main function (Calling function)

body of statement in main function

Comments

User-defined function name (Called function)

Body of statement in user-defined function

Program example void main( ) { printf ( "\ni am in main function" ) ; italy( ) ; printf(“\n i am in middle of main”); brazil( ) ; printf(“\n i am back to main”); getch(); } italy() { printf(“\n Hi how are you?”); } brazil() { printf(“\n Hmmm, not bad!”); }

Output: ?

Output:

I am in main function Hi how are you? I am in middle of main Hmmm, not bad I am back to main

Why use function?

• Writing functions avoids rewriting the same code over and over.

• Separating the code into modular functions makes the program easier to design and understand.

Function categories on the basis of argument_list and return_type

• 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 return values

Function with no arguments and no return values

#include<stdio.h> #include<conio.h> void my_sms(void); void main() { printf(“\n send me a message”); my_sms(); my_sms(); } void my_sms() { print(“\n plz rd my msg.”); }

output: send me a message plz rd my msg plz rd my msg

Function prototype declaration

Function with arguments and no return values

#include<stdio.h> void factorial(int); void main() { int n; printf(“\n enter a no.”); scanf(“%d”, &n); factorial(n); getch(); } void factorial(int m) { int i,f=1; for(i=1;i<=m;i++) f=f*i; printf(“\n factorial of %d is %d”, m,f); }

Output: Enter a no. 5 Factorial of 5 is 120

Function with arguments and return values

#include<stdio.h> int compute(int,int); void main() { int n1=100,n2=500,ans; ans=compute(n1,n2); printf(“\n largest no=%d”,ans); getch(); } int compute(int x,int y) { if(x>y) return x; else return y;

#include<stdio.h> float add (int,int); void main() { float n1,n2,ans; printf(“\n enter 2 no.”); scanf(“%f%f”,&n1,&n2); ans=add(n1,n2); printf(“\n sum=%f”,ans); getch(); } float add(int a,int b) { float result; result=a+b; return result; }

Function with No arguments and return values

#include<stdio.h> #include<conio.h> int p(); void main() { int my_p; clrscr(); my_p=p(); printf("\n power = %d", my_p); getch(); }

int p() { int i,power=1,n; printf("\n enter value for power:");

scanf("%d",&n); for(i=1;i<=n;i++) power=power*n; return power; } Output: enter value for power: 5

Power= 3125 55= 5 x 5 x 5 x 5 x 5=3125

Excercise

Exercise:

void main(){ int i = 10, j = 20 ; printf ( "%d %d %d ", i, j ) ; printf ( "%d", i, j ) ; }

void main() { int a = 1 ; printf ( "%d %d %d", a,++a,a++ ) ; }

Output: 3 3 1

Output; 10 20 860 10

Garbage value

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assignment

• WAP to find the factorial of a number using function with arguments and return value

• Wap to find the cube of a number using function with argument but no return value

• Write a c function which returns the biggest of 3 numbers.

• Do the exercise from Let-Us-C

Function Prototype

Declaring a function is function prototype which provides the compiler with a description that will be defined at a later point in the program.

Syntax:

Return_type function_name(arg-type-1,arg-type-2,……..arg-type-n);

Example:

int my_square(int);

double amount(int,float,int);

void useless_msg(char[],int);

Function definition • An actual function is a snippet code that gets

executed.

• First line of function definition (known as function header) should be identical to function prototype with no semicolon.

• Example: int my_square(int x)

long int my_sq;

my_sq=x*x;

return my_sq;

Snippet code

Actual and Formal Parameter #include<stdio.h> int compute_sum(int,int); void main() { int sum,n1=10,n2=30; sum=compute_sum(n1,n2); printf(“total =%d”,sum); getch(); } int compute_sum(int x, int y) { return (x+y); }

Actual Arguments (or Actual Parameter)

Formal Parameter

Variable used in Calling function

Variable used in Called function

Actual & Formal Parameter example

#include<stdio.h> void plz_do_it(int); void main( ) { int a = 30 ; plz_do_it ( a ) ; printf ( "\n%d", a ) ; } void plz_do_it ( int b ) { b = 60 ; printf ( "\n%d", b ) ; }

Output: 60 30

#include<stdio.h> square (float); void main() { int a; printf(“\n enter a number”); scanf(“%f”,&a); printf(“%f”,square(a)); } square(float x) { return (x*x); }

Output Enter a number: 2 4.00000 Enter a number: 2.5 6.000000

Actual & Formal Parameter example #include<stdio.h> void plz_do_it(int); void main( ) { int a = 30 ; plz_do_it ( a ) ; printf ( "\n%d", a ) ; } void plz_do_it ( int b ) { b = 60 ; printf ( "\n%d", b ) ; }

Output: 60 30

#include<stdio.h> float square (float); void main() { int a; printf(“\n enter a number”); scanf(“%f”,&a); printf(“%f”,square(a)); } float square(float x) { return (x*x); }

Output Enter a number: 2 4.00000 Enter a number: 2.5 6.000000

Output Enter a number: 2 4.00000 Enter a number: 2.5 6.250000 Enter a number:1.5 2.250000

correct

Scope Rules

• The scope of a variable is in the program or function in which it is declared.

• A global variable is visible to all contained functions including the function in which the variable is declared.

• An entity* declared in the scope of another entity is always a different entity even if their names are identical.

entity*= variable, function, parameter

Scope Rule (contd…) 1. The scope of a variable is in the program or

function in which it is declared.

#include<stdio.h> void add(int,int); void mul(int,int); void main() { int a=20,b=10; add(a,b); mul(a,b); }

void add(int x1,int x2) { printf(“\n sum=%d”,x1+x2); }

void mul(int y1,int y2) { printf(“\n multiplication=%d”,y1*y2); }

Scope of variable a,b is within the main() only. Scope of variable x1,x2 is within the add() only. Scope of variable y1,y2 is within the mul() only.

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Scope Rule (contd…)

2. A global variable is visible to all contained functions

including the function in which the variable is declared.

#include<stdio.h> int add_me(); int n1,n2; void main() { int my_sum; my_sum=add_me(); printf(“\n sum=%d”,my_sum); } /* end of main*/ int add_me(){ int result; Result=n1+n2; return result; }

Global variable

Local Variable A variable declared inside of a function. They are unknown to other function. i.e. scope is only within the function in which They are declared. Variable are Not accessed outside of function.

A variable declared outside of a function. They are known or accessed by any function comprising the program.

Scope Rules (contd…)

• An entity* declared in the scope of another entity is always a different entity even if their names are identical.

entity*= variable, function, parameter

Example; ??????

Parameter passing method

Pass by Value

Or Call by value

Pass by Reference

Or Call by Reference

Parameter passing method on the basis of argument (or parameter)

When the values of arguments are passed From the calling function to the called function, The values are copied into called function. If any changes made to the value in calling function, There is no change in the original values within the calling function.

Actual values are not passed, instead their addresses are passed. There is no copying of values since their memory locations are referenced. If any changes is made to value in called function, The original value gets changed within the calling function.

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Call by values

//swaping the value by callByValue #include<stdio.h> void call_by_value(int,int); void main( ) { int a = 10, b = 20 ; call_by_value ( a, b ) ; printf ( "\na = %d \t b = %d", a, b ) ; } void call_by_value ( int x, int y ) { int t ; t = x ; x = y ; y = t ; printf ( "\nx = %d \t y = %d", x, y ) ; }

//no change in calling function #include<stdio.h> void no_change_value(int); void main( ) { int a = 30 ; no_change_value ( a ) ; printf ( "\na=%d", a ) ; } void no_change_value ( int b ) { b = 60 ; printf ( "\nb= %d", b ) ; }

Output: B=60 A=30

Output: x = 20 y = 10 a = 10 b = 20

Pointer (know it before using call by reference)

Let us take an example, int i=3;

This declaration tells the C compiler to:

(a) Reserve space in memory to hold the integer value.

(b) Associate the name i with this memory location.

(c) Store the value 3 at this location.

Location name

Value at location

Location number

Memory map For i’s location

Pointer (contd…)

Location name

Value at location

Location number

Memory map For i’s location

void main( ) { int i = 3 ; printf ( "\nAddress of i = %u", &i ) ; printf ( "\nValue of i = %d", i ) ; }

output: Address of i = 65524 Value of i = 3

%u=unsigned integer

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Pointer (contd…) &(address operator) and *(indirection operator)

main( ) { int i = 3 ; printf ( "\nAddress of i = %u", &i ) ; printf ( "\nValue of i = %d", i ) ; printf ( "\nValue of i = %d", *( &i ) ) ; } output: Address of i = 65524 Value of i = 3 Value of i = 3

main( ) { int i = 3 ; printf ( "\nAddress of i = %u", &i ) ; printf ( "\nValue of i = %d", i ) ; } output: Address of i = 65524 Value of i = 3

* is known as ‘indirection operator’ or

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Pointer (contd…)

main( ) { int i = 3 ; int *j ; j = &i ; printf ( "\nAddress of i = %u", &i ) ; printf ( "\nAddress of i = %u", j ) ; printf ( "\nAddress of j = %u", &j ) ; printf ( "\nValue of j = %u", j ) ; printf ( "\nValue of i = %d", i ) ; printf ( "\nValue of i = %d", *( &i ) ) ; printf ( "\nValue of i = %d", *j ) ; }

Output: Address of i = 65524 Address of i = 65524 Address of j = 65522 Value of j = 65524 Value of i = 3 Value of i = 3 Value of i = 3

Pointer variable (‘j’ in this case) contains address of other

variable (‘i’ in this case)

65524 3

Call by reference

//swapping the value by reference #include<stdio.h> void call_by_reference(int*, int*); void main( ) { int a = 10, b = 20 ; printf(“\n before swapping\n”); printf(“\n a=%d \t b=%d”,a,b); call_by_reference( &a, &b ) ; printf(“\n after swapping\n”); printf ( "\na = %d b = %d", a, b ) ; }

Output: before swapping a=10 b=20 after swapping a=20 b=10

void call_by_reference( int *x, int *y )

{ int t ; t = *x ; *x = *y ; *y = t ; }

Call by value vs call by reference

Call by value Call by reference

It consumes more memory space because formal parameter also occupies memory space.

It consumes less memory space because irrespective of data type of the actual arguments, each pointer occupies only 4 bytes

It takes more time to execute because the values are copied.

It takes less time because no values are copied.

Exercise

• Write a C program using function to find the numbers between 1 to 1000 which follows the property that 12 possesses. i.e.

(a) The number is 12

(b) Take it reverse (i.e.21) and square it (i.e. 441)

(c) Now take the square of 12 (i.e. 144)

(d) Compare the result of step (b) & step (c)

(e) If they are reverse of each other then print 12.

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Recursion(A recursive function)

• A function is called ‘recursive’ if a statement within the body of a function calls the same function.

• Sometimes called ‘circular definition’, recursion is thus the process of defining something in terms of itself.

• A situation in which a function calls itself either directly or indirectly.

Recursion (contd…)

e.g. Recursion can be used to calculate factorial of a number. X!= x* (x-1)* (x-2)*(x-3)*…*2*1 However x! may be calculated as X!=x*(x-1)! And then (x-1)!= (x-1)*(x-2)! And then (x-2)!=(x-2)*(x-3)! ------------------------ ---------------------- And so on……

e.g. find the factorial of 4 4!=4*3*2*1 Or 4!=4*3!

Recursion example Q. find the factorial of a number using recursion

main( )

int a, fact ;

printf ( "\nEnter any number " ) ;

scanf ( "%d", &a ) ;

fact = rec ( a ) ;

printf ( "Factorial value = %d", fact ) ;

rec ( int x ) { int f ; if ( x == 1 ) return ( 1 ) ; else return (x * rec ( x - 1 )) ; }

Recursion concept understanding

return ( x * rec ( x - 1 )) ;

Important line

rec ( 5 ) returns ( 5 times rec ( 4 ), which returns ( 4 times rec ( 3 ), which returns ( 3 times rec ( 2 ), which returns ( 2 times rec ( 1 ), which returns ( 1 ) ) ) ) )

Recursion flow example

Starts here

Assignment on recursion

1. Find the factorial of a given number using recursion.

2. Generate fibonacci series upto nth terms using recursion

3. Define power function using recursion

4. Find the greatest common divisor (GCD) of 2 no.

5. Conversion from decimal to binary

Special assignment on function

• Go through Let-Us-C of chapter function

• Try to generate your own function, say myf()

• Save a defined function myf() with new .cpp file name , say myf.cpp

• Save a new header file with declaring myf() prototype, say myf.h

• Add this header file myf.h to TurboC library

• Include this header file in your new file and execute the statement, #include ”myf.h”

1. do_it(). 2.print_me(). 3.add_me() 4.print_table()

Data Storage in C

1.Variable’s value stores at two location: • Memory and • CPU Register

2.Variable’s storage class tells us: Where the value would be stored. Default initial value Scope of a variable Life of a variable

Data storage

Automatic

Register Static External

Type of Storage Class

Automatic Storage Class (keyword:auto)

• Storage- Memory

• Default Initial Value- garbage value

• Scope- local to the block in which variable is defined

• Life- within the block

void main( ) { auto int i, j ; printf ( "\n%d %d", i, j ) ; } Output: 1211 221

Garbage value

void main( ) { auto int i = 1 ; { { { printf ( "\n%d ", i ) ; } printf ( "%d ", i ) ; } printf ( "%d", i ) ; } }

Output: 1 1 1

Automatic Storage class example

void main( ) { auto int i = 1 ; { auto int i = 2 ; { auto int i = 3 ; printf ( "\n%d ", i ) ; } printf ( “\n%d ", i ) ; } printf ( “\n%d", i ) ; }

Output: 3 2 1

Register storage class

• Storage - CPU registers.

• Default initial value - Garbage value.

• Scope - Local to the block in which the variable is defined.

• Life - remains within the block in which the variable is defined.

void main( ) { register int i ; for ( i = 1 ; i <= 10 ; i++ ) printf ( "\n%d", i ) ; }

Register variable is used to use the

variable frequently.

Static Storage class • Storage − Memory.

• Default initial value − Zero.

• Scope − Local to the block in which the variable is defined.

• Life − Value of the variable persists between different function calls.

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void main( ) { increment( ) ; increment( ) ; increment( ) ; }

increment( ) { static int i = 1 ; printf ( "%d\n", i ) ; i = i + 1 ; }

Output: 1 2 3

auto int i=1; Output: 1 1 1

External Storage Class (keyword:extern)

• Storage − Memory. • Default initial value − Zero. • Scope − Global. • Life − As long as the program’s execution doesn’t come to an end.

int i ; main( ) { printf ( "\ni = %d", i ) ; increment( ) ; increment( ) ; decrement( ) ; decrement( ) ; }

increment() { i = i + 1 ; printf ( "\non incrementing i = %d", i ) ; }

decrement( ) { i = i - 1 ; printf ( "\non decrementing i = %d", i ) ; }

Output: i = 0 on incrementing i = 1 on incrementing i = 2 on decrementing i = 1 on decrementing i = 0

Extern Storage Class Example

int x = 21 ;

void main( )

extern int y ;

printf ( "\n%d %d", x, y ) ;

int y = 31 ;

Declaring a variable

Defining a variable

global

Requires no space

space gets reserved

Extern storage class example (contd…)

int x = 10 ; main( ) { int x = 20 ; printf ( "\n%d", x ) ; display( ) ; } display( ) { printf ( "\n%d", x ) ; }

Global x

Local x Confused ?

Output: 20 10

Preference is given to local variable

Excercise

• From Let-Us-C

Function lecture

Education