C programming slide-6

Wednesday, April 12, 2023

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PREPARED BY:-PRADEEP DWIVEDI

(pursuing B.TECH-IT)

FROM H.C.S.T.(MATHURA)

Mob-+919027843806

[email protected]

C-PROGRAMMING SLIDE-6

PRADEEP DWIVEDI(pur.B.TECH-IT)

Wednesday, April 12, 2023PRADEEP DWIVEDI(pur.B.TECH-IT)

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C-6

TOPIC:- USER DEFINED FUNCTION POINTERS


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PART-6.1


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USER DEFINED FUNCTION

Every c program collection of one or more functions.

It consist some predefine function and some user define function.

main() is a user define function which is first executed.


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ELEMENTS OF A USER DEFINED FUNCTION


1. Function prototyping/declaration.2. function definition.3. function invocation/calling.


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FUNCTION DECLARATION/PROTOTYPING


Like variables , all functions in a c program must be declared, before they are invoked.

A function declaration (also known as function prototype) consists of four parts-

1. function type(return type).

2. function name.

3. parameter list.

4. terminating semicolon.

eg:-

int sum(int a,int b);

or int sum(int,int);


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FUNCTION DECLARATION/PROTOTYPING

return type(function type) specifies that what type of value do you want to return.

function name specifies the name of function this can be anything which do you want.

in parameterized function at the time of declaration we specifies the parameter in parentheses as data type of parameter. (variable is optional)

in declaration of a function after parentheses we must terminate by semicolon(;).


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DEFINITION OF FUNCTION

A function definition, also known as function implementation shall include the following elements.

1. Function name.2. Function type.3. List of parameter.4. Local variable declaration.5. Function statement.6. A return statement.


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DEFINITION OF FUNCTION

Format of function definition given by a example-

int sum(int a,int b){c=a+b;return c;}

Function_type(return_type)

Function name

Parameter list

Function statement

return statement


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FUNCTION CALLING


A function can be called by simply using the function name followed by the list actual parameter(if any), enclosed by parenthes.

eg:- y=sum(5,10); when we call our function that time we

sends the control to the body of a function.


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prog1

//this demo is for use defined function.

#include<stdio.h>

#include<conio.h>

void main()

{

void message();

clrscr();

message();

printf("I, am in main\n");

getch();}void message(){printf("Hello, I am

pradeep dwivedi\n");}


function declaration

function calling

control comes here

print this line


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NOTE


We can declare and invoke a function inside another function . But we can not define the body of a function inside any other function.

Function execution always depends on function invocation . It never depends on the declaration or the definition.

main() is a predefined function which declared in c library and called by the c compiler. so there is no need to declare or call the main() function and only define the body of main() function.


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PROG2

//prog2#include<stdio.h>#include<conio.h>void main(){void italy();void brazil();

void argentina();clrscr();printf("I am in main\n");italy();brazil();argentina();

getch();}void italy(){printf("I am in italy\n");}void brazil(){printf("I am in brazil\n");}void argentina(){printf("I am in argentina");}

Function declaration

Function calling

Control comes here

Print this line


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NOTE

When we invoke a function inside another function these always execute in stack form.

In other words , a function that is invoked at last would we the first one two finish.


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prog3

//prog- function call inside another function.

#include<stdio.h>#include<conio.h>void main(){void italy(); printf("I am in main() \n");italy(); printf("I am finally back in main()\

n");getch();}void italy(){void brazil();

printf("I am in italy\n");brazil();printf("I am back in italy\n");}void brazil(){void argentina();printf("I am in brazil\n");argentina();}void argentina(){printf("I am in argentina\n");}


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return KEYWORD

return is a keyword with the help of that we return a value and a value is always returned where from the function being called.

in the case of main() function value is return to the compiler. because main() function called by the compiler.


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PART-6.2


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CATEGORIES OF A FUNCTION


On the bases of parameter function can be categories into two categories.

Non parameterized function are those function in which we do not pass any parameter.

Parameterized function are those function in which we pass a parameter.

Categories of function

parameterizedNon

parameterized


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Prog4(based on parameterized-function)

//w.a.p. to add two number by using parameterized function

#include<stdio.h>#include<conio.h>void main(){int a,b,sum;int calsum(int,int);clrscr();printf("Enter two values");scanf("%d%d",&a,&b);

sum=calsum(a,b);printf("\n sum=

%d",sum);getch();}int calsum(int x,int y){int d;d=x+y;return(d);}


Function declaration

Function calling


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TERMS RELATED TO PROGRAM


the declaration of variable specifies that when we call the calsum() function it take two integer value.

when we call calsum(a,b); function it takes two parameter and these values are stored in variable x and y.

after calculating the expression d=a+b; the value of d is returned where from which the function is called and the value of d is stored in variable sum.

in nest statement the value of sum is printed out.


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PARAMETERIZED FUNCTION

to invoke(call) a parameterize function there are two ways-

1. call by vale.2. call by reference.


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CALL BY VALUE

if we pass the value as a function parameter that is known as call by value.

in call by value if we make some changes in the called function these changes will not be appeared at the original place. (in the calling function).

calling function are those function those invoke any other function.(where the function is being calling).

called function are those function those are invoked by any other function.

in the call by value the variable always maintain the separate-separate copy for the calling function and called function that is why no changes are reflected takes place.


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prog5

//prog to swap the variable (using call by value).

#include<stdio.h>#include<conio.h>void main(){int a=10;int b=20;clrscr();void swapv(int,int);swapv(a,b);printf("a=%d\n",a);printf("b=%d\n",b);getch();}

void swapv(int x,int y)

{int t;t=x;x=y;y=t;printf("x=%d\n",x);printf("y=%d\n",y);}

control comes herewith x=10

y=20


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CALL BY REFERENCE

when we pass address as a function parameter this is called call by reference.

in call by reference, if we make some changes into the called function, these changes will also be appeared in the calling function. because they don’t maintain the separate copy of the variables.

CALL BY REFERENCE DISCUSSED IN DETAIL AFTER STUDYING THE

POINTERS


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PART-6.3


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POINTER

A pointer is a derived data type in c. it is built from one of the fundamental data types available in c.

Pointer variable is a special variable that holds the address of any other variable.

If we want to hold the address of any integer variable that time we need an integer pointer variable and so on.

A pointer variable prefix asterisk sign(*) at declaration time.

Eg:- int *p;


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TAKE AN EXAMPLE FOR UNDERSTANDING POINTER

int a=20; it stores in memory as- a 5000 these address is stored as-

&a=5000(address of 20

integer variable declaration

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TAKE AN EXAMPLE FOR UNDERSTANDING POINTER

to store the address we declare a pointer variable-

int *p; p=&a; (p is a pointer variable which holds the

address) *p=25; (means this stores the 25 at address

5000)

integer pointer variable declaration

p=5000

value at address


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POINTER DECLARATION STYLE pointer variables are declared similarly as

normal variables except for the addition of unary * operator.

this symbol can appear anywhere between the type name and the pointer variable name.

programmers use the following styles- int* p; int *p; int * p;

style 1

style 2(generally used)

style 3


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prog6

//Demo for pointer#include<stdio.h>#include<conio.h>void main(){int i=3,*x;float j=1.5,*y;char k='c',*z;printf("the value of i=%d\n",i);printf("the value of j=%f\n",j);printf("the value of k=%c\n",k);x=&i;y=&j;z=&k;

printf("original value of x=%d\n",x);

printf("original value of y=%d\n",y);

printf("original value of z=%d\n",z);

x++;y++;z++;printf("new value of x=%d\n",x);printf("new value of y=%d\n",y);printf("new value of z=%d\n",z);getch();}



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EXPLAINATIONstep1 I j k x y z

10 20 30 40 50 60step2

10 20 30 40 50 60step3

10 20 30 40 50 60

3 1.5 c variable

address(suppose)3 1.5 c 10 20 30

3 1.5 c 12 24 31


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POINTER INCREMENT AND SCALE FACTOR

when we increment a pointer, its value is increased by the length of the data type. this length is called scale factors.

eg:- let p1 is an integer pointer with an initial value says- 2800,

then after operation p1=p1+1; the value of it will be 2802 , and not 2801.

the length of various data type are as follows- character 1 byte integer 2 bytes float 4 bytes long integer 4 bytes double 8 bytes


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prog7

//This demo is for pointer increment and scale factorvoid main(){int i=4,*j,*k;clrscr();j=&i;printf("The value of j:%d\n",j);j=j+1;printf("The value of j:%d\n",j);k=j+3;printf("The value of k:%d\n",k);getch();}


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POINTER EXPRESSION

int *p1,*p2; y=*p1 * *p2;=(*p1)*(*p2) z=*p1/*p2 we may not use pointers in division or

multiplication. p1/p2 p1*p2 p1/3

valid(because these are

the value at address)

invalid(because these are

the address)

c allows us to add integers to or subtract integers from pointers, as well as to subtract one pointer from another.p1+4;p2-2; p1-p2;


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RULES FOR POINTER OPERATION a pointer variable can be assigned the address of another variable. a pointer variable can be assigned the value of another pointer

variable. a pointer variable can be assigned with zero or NULL value. a pointer variable can prefixed or post fixed with increment or

decrement operator. an integer value may be added or subtract a pointer variable. when two pointer point to the same array, one pointer variable can be

subtracted from another. when two pointer points to the object of same data types, they can be

compared using relational operator. a pointer variable can’t be multiplied by a constant. two pointer variable can’t be added a value can not be assigned to an arbitary address.

(i.e. & =10 is illegal)


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CHAIN OF POINTER

int a=10;

p2 p1 a

p1 holds the address of integer variable

p2 holds the address of integer pointer

variable

int *p1;p1=&a;

int **p2;p2=&p1;

valueaddress1address2


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prog8

//prog-for chain of pointer#include<stdio.h>#include<conio.h>void main(){int x,*p1,**p2;clrscr();x=100;p1=&x;p2=&p1;printf("Address of a=%d\n",p1);printf("Address of p1=%d\n",p2);printf("Value at address p1=%d\

n",**p2);printf("Value at address p2=%d\

n",*p2);getch();}

explanation:- in last statement

second last statement

**p2=*(*p2) =*(value at

address p2)=*(p1)=value at address p1=100


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PART-6.4


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POINTER vs ARRAY

Array is also used to hold the address but, array variable used to holds the base address of an array.

The term base address means address of very first element in the array.

Suppose we declare an array-int x[5]={1,2,3,4,5};


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POINTER vs ARRAY

x[0] x[1] x[2] x[3] x[4]

element

value 1000 1002 1004 1006 1008 address

base addressi.e. x=&x[0]=1000;

1 2 3 4 5

x+1=&x[1]=1002x+2=&x[2]=1004x+3=&x[3]=1006x+4=&x[4]=1008

with the help of base address we can calculate the address of any element by

using its index and the scale factor of the data type

address of x[3]=base address+(3*scale factor of int)

=1000+(3*2)=1006


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IMPORTANT POINT

An array variable is always having address of it zero index by default.

Array variable can hold the address of only zero index element these can not hold the address of any other element.

But pointer can hold the address of any element in the list.

An array variable is a reference variable it is little bit similar with pointer.


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prog9

//prog- pointer vs array#include<stdio.h>#include<conio.h>void main(){int

arr[]={10,20,36,72,45,36};

int *j,*k;clrscr();j=&arr[4];k=(arr+4);if(j==k)

printf("Two pointers point two the same location");

elseprintf("Two pointers

do not point to the same location");

getch();}


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prog10

//wap to sibtract a pointer from anoter pointer

#include<stdio.h>#include<conio.h>void main(){int arr[]={10,20,30,40,60,57,56};int *i,*j;clrscr();i=&arr[1];j=&arr[5];printf("value of i:%d\n",i);

printf("value of j:%d\n",j);

printf("The value at address i:%d\n",*i);

printf("The value at address j:%d\n",*j);

printf("The difference between address: %d\n",j-i);

printf("The difference between values is %d\n",*j-*i);

getch();}


I THINK THERE IS NO NEED TO EXPLIAN

THIS PROGRAM


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REMOVE CONFUSION

I think pointer is very confusing topic in “C”

Here we try to remove confusion – Suppose - int *p; Pointer variable declared with (*) sign

such as (*p) but address is stored in p not *p

*p is always store the value at address

Pointer variable declaration


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POINTER AND CHARACTER STRINGS

The character arrays are declared and initialized as follows:-

char str[5]=“good”; The compiler automatically inserts the null

character ‘\0’ at the end of the string. C supports an alternative method to create string

using pointer variable of type char.eg: char *str=“good”;

Remember, although str is a pointer to the string, it is also the name of string .therefore, we don’t need to use indirection operator(*) here.


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NOTE

When we want to print the string, that time we use the format string (%s).

and if we want to print the address of string that time we use format string (%d) or (%u)


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PROG11


//PROG POINTER VS CHARACTER ARRAY#include<stdio.h>#include<conio.h>void main(){char arr[]="PRADEEP DWIVEDI";char *s="HINDUSTAN COLLEGE OF SCIENCE AND TECHNOLOGY";clrscr();printf("%s\n",arr);printf("%s\n",s);printf("%d %d",arr,s);getch();}


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SIZE OF OPERATOR

With the help of sizeof operator we can find out the size of value or variable that is occupied in the memory.

Note:- each and every pointer variable always

occupied two bytes in memory either it is float or char or int or etc.


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prog12.c

//PROG- DEMO FOR SIZE OF OPERATOR.#include<stdio.h>#include<conio.h>void main(){char arr[10]="HINDUSTAN";char *s="HINDUSTAN";float *p;clrscr();s++;//arr++;printf("%s\n",arr);printf("%s\n",s);printf("%d %d %d",sizeof(s),sizeof(arr),sizeof(p));getch();}

print HINDUSTANprint INDUSTAN BECAUSE ADDRESS OF S IS

INCREASED BY ONE CHARACTER


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CALL BY REFERENCE

when we pass address as a function parameter this is called call by reference.

in call by reference, if we make some changes into the called function, these changes will also be appeared in the calling function. because they don’t maintain the separate copy of the variables.


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prog13

//PROG-WAP FOR SWAPINGvoid main(){int a=10;int b=20;void swapv(int*,int*);clrscr();swapv(&a,&b);printf("a=%d\n",a);printf("b=%d\n",b);getch();}

void swapv(int *x,int *y){int t;t=*x;*x=*y;*y=t;printf("*x=%d\n",*x);printf("*y=%d\n",*y);getch();}

WHEN WE RUN THIS PROGRAM THIS PROGRAM PRODUCE THE CHANGE IN SWAPV FUNCTION AND MAIN FUNCTION ALSO BECAUSE VALUE IS CHANGE AT ADDRESS

print the value at addres 20 10


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FUNCTION RETURNING POINTER When we declare a function as pointer

type then function return pointer type value (address ).


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prog14

//PROG- TO FIND THE MAXIMUM NUMBER

#include<stdio.h>#include<conio.h>int *larger(int*,int*);//prototypevoid main(){int a=10;int b=20;int *p;clrscr();p=larger(&a,&b);//function callprintf("Greater number is:

%d",*p);getch();

}int *larger(int *x,int *y){if(*x>*y)return(x);//address of aelsereturn(y);//address of b}try to under stand it self

C programming slide-6

Education

function prototype

function implementation

function invocationcalling

parameterized function

function callingfriday

techit10a function

techit8a function definition

partsfunction typereturn