Program for Largest Number among three numbers

Program for Largest Number among three numbers

/* c program to find largest number among 3 numbers*/

#include <stdio.h> 

int main()

{

    int a,b,c;

    int largest;

    printf("Enter three numbers :");

    scanf("%d%d%d",&a,&b,&c);

    if(a>b && a>c)        

        largest=a;

    else if(b>a && b>c)       

        largest=b;

    else

        largest=c;

    printf("Largest number is = %d",largest); 

    return 0;

}

Program to get ASCII of a character in C

Program to get ASCII of a character in C

#include <stdio.h>
int main()
{
char ch;
printf("Enter the character: ");   //input character
scanf("%c",&ch);
printf("ASCII is = %d\n", ch);
return 0;
}

File Handling in C

File Input/Output : C files I/O functions handle data on a secondary storage device, such as a hard disk.

C can handle files as Stream-oriented data (Text) files, and System oriented data (Binary) file.

In C language, we use a structure pointer of file type to declare a file. FILE *fp;

C provides a number of functions that helps to perform basic file operations. 

Following are the functions.

Function	Description
fopen()	create a new file or open a existing file
fclose()	closes a file
getc()	reads a character from a file
putc()	writes a character to a file
fscanf()	reads a set of data from a file
fprintf()	writes a set of data to a file
getw()	reads a integer from a file
putw()	writes a integer to a file
fseek()	set the position to desire point
ftell()	gives current position in the file
rewind()	set the position to the beginning point

C File Operations : Five major operations can be performed on file are:  

1. Creation of a new file. 
2. Opening an existing file. 
3. Reading data from a file. 
4. Writing data in a file.
5. Closing a file.

Opening a File or Creating a File 

The fopen() function is used to create a new file or to open an existing file.

General Syntax:

*fp = FILE *fopen(const char *filename, const char *mode);

Here, *fp is the FILE pointer (FILE *fp), which will hold the reference to the opened(or created) file.

Filename is the name of the file to be opened and mode specifies the purpose of opening the file. Mode can be of following types.

Mode	Description
r	opens a text file in reading mode
w	opens or create a text file in writing mode.
a	opens a text file in append mode
r+	opens a text file in both reading and writing mode
w+	opens a text file in both reading and writing mode
a+	opens a text file in both reading and writing mode
rb	opens a binary file in reading mode
wb	opens or create a binary file in writing mode
ab	opens a binary file in append mode
rb+	opens a binary file in both reading and writing mode
wb+	opens a binary file in both reading and writing mode
ab+	opens a binary file in both reading and writing mode

Closing a File

The fclose() function is used to close an already opened file.

Syntax :  int fclose( FILE *fp);

Here fclose() function closes the file and returns zero on success, or EOF if there is an error in closing the file. 

This EOF is a constant defined in the header file stdio.h. 

Input/Output operation on File

Example:

#include<stdio.h>

int main()

{

    FILE *fp;

    char ch;

    fp = fopen("one.txt", "w");

    printf("Enter data...");

while( (ch = getchar()) != EOF)

{

        putc(ch, fp);

    }

    fclose(fp);

    fp = fopen("one.txt", "r"); 

    while( (ch = getc(fp)! = EOF)

    printf("%c",ch);          // closing the file pointer

    fclose(fp);

return 0;

}

Reading and Writing to File using fprintf() and fscanf()

Example:

#include<stdio.h>

struct emp

{

    char name[10];

int age;

};

void main()

{

    struct emp e;

    FILE *p,*q;

    p = fopen("one.txt", "a");

    q = fopen("one.txt", "r");

    printf("Enter Name and Age:");

    scanf("%s %d", e.name, &e.age);

    fprintf(p,"%s %d", e.name, e.age);

    fclose(p);

    do

    {

        fscanf(q,"%s %d", e.name, e.age);

        printf("%s %d", e.name, e.age);

    }

while(!feof(q));

}

In this program, we have created two FILE pointers and both are referring to the same file but in different modes.

fprintf() function directly writes into the file, while fscanf() reads from the file, which can then be printed on the console using standard printf() function.

Reading and Writing in a Binary File : A Binary file is similar to a text file, but it contains only large numerical data. The Opening modes are mentioned in the table for opening modes above.

fread() and fwrite() functions are used to read and write is a binary file.

Syntax: 

fwrite(data-element-to-be-written, size_of_elements, number_of_elements, pointer-to-file);

fread() is also used in the same way, with the same arguments like fwrite() function.

Below mentioned is a simple example of writing into a binary file

Example:

const char *mytext = "The quick brown fox jumps over the lazy dog";   

FILE *bfp= fopen("test.txt", "wb");   

if (bfp)

{     

    fwrite(mytext, sizeof(char), strlen(mytext), bfp);     

fclose(bfp);  

}

fseek(), ftell() and rewind() functions

fseek() : It is used to move the reading control to different positions using fseek function.

ftell() : It tells the byte location of current position of cursor in file pointer.

rewind() : It moves the control to beginning of the file.

 

Pointers in C

Pointer : A Pointer in C language is a variable which holds the address of another variable of same data type. 

Sytnax:

datatype *variable_name;

Example:

int  *salary;        //integer type pointer

char  *alphabet;    // character type pointer

Concept of Pointers : When a variable is declared in a c program, system allocates a location to hold the assigned value. This location has its own address number. A pointer can also be used to refer another pointer, function. 

A pointer can be incremented/decremented, i.e., to point to the next/ previous memory location.

 Operators that are used with Pointers

"Address of" (&) Operator

"Value at Address" (*) Operator

Example:

int a=10;

int *p;        // declaring integer type pointer ‘p’

p=&a;       // assigning address of ‘a’ to pointer ‘p’

   

printf(‘’%d’’,&p);  // print address of ‘p’ that is 3002

printf(“%d”,*p);    // print the value of ‘a’ that is 10

Benefits of pointers:

1. Pointers allow passing of arrays and strings to functions more efficiently.

2. Pointers make it possible to return more than one value from the function.

3. Pointers reduce the length and complexity of a program.

4. Pointers increase the processing speed.

5. Pointers save the memory.

Example:

#include<stdio.h>

int main ()

{

int n = 20, *ptr;  

ptr = &n;        /

printf(“Address of n variable: %d\n”, &n ); 

printf("Address stored in ptr variable: %d\n", ptr ); 

printf("Value of *pntr variable: %d\n", *ptr );

return 0;

}

Example:

int i = 12, *ip = &i;

double d = 2.3, *dp = &d;

char ch = 'a', *cp = &ch;

Suppose the address of i, d and ch are 1000, 2000, 3000 respectively, therefore ip, dp and cp are at 1000, 2000, 3000 initially.

Pointer Arithmetic on Integers

ip = ip + 1	ip = ip + 1 = 1000 + 1*4 = 1004
ip++ or ++ip	ip++ = ip + 1 = 1004 + 1*4 = 1008
ip = ip + 5	ip = ip + 5 = 1008 + 5*4 = 1028
ip = ip - 2	ip = ip - 2 =1028 - 2*4 = 1020
ip-- or --ip	ip = ip + 2 = 1020 + 2*4 = 1028

Pointer Arithmetic on Float

dp + 1	dp = dp + 1 =2000 + 1*8 = 2008
dp++ or ++dp	dp++ = dp+1 = 2008+1*8 = 2016
dp = dp + 5	dp = dp + 5 = 2016+5*8 =2056
dp = dp - 2	dp = dp - 2 = 2056-2*8 = 2040
dp-- or --dp	dp = dp - 1 = 2040-1*8 = 2032

Pointer Arithmetic on Characters

cp + 1	cp = cp + 1 = 3000 + 1*1 = 3001
cp++ or ++cp	cp = cp + 1 = 3001 + 1*1 = 3002
cp = cp + 5	cp = cp + 5 = 3002 + 5*1 = 3007
cp = cp - 2	cp = cp + 5 = 3007 - 2*1 = 3005
cp-- or --cp	cp = cp + 2 = 3005 - 1*1 = 3004

Pointer to Pointer

Syntax:

data_type **p;

Example:

int a= 10;

int *p = &a;

int **q = &p;

Here p is of type (int *) or pointer to int, q is of type (int **) or pointer to pointer to int.

**q =*(*q)     // both are same

Example:

#include<stdio.h>

int main()

{

    int a = 10;

    int *p = &a;

    int **q = &p;

    printf("Value of a = %d\n\n", a); 

    printf("Address of a = %u\n", &a);

    printf("Value of p = %d\n\n", p);

    printf("Address of p = %u\n", &p);

    printf("Value of q = %d\n\n", q);

    printf("Value of *q = value of p = %d\n", *q);

    printf("Value of **q = value of a = %d\n\n", **q);

   return 0;

}

Pointer to Array

Example:

#include <stdio.h>

int main()

{

    int i;

    int a[5] = {1, 2, 3, 4, 5};

    int *p = a;           // same as int *p = &a[0]

    for (i = 0; i < 5; i++)

    {

        printf("%d", *p);

        p++;

    }

    

return 0;

}

Note: *(a+i)  is same as  a[i]

Pointer to Multidimensional Array

generalized form for using pointer with multidimensional arrays.

*(*(a + i) + j) which is same as, a[i][j]

Pointer and Character strings

Pointer can also be used to create strings. Pointer variables of char type are treated as string.

char *str = "HelloWorld"; 

Or

char *str;

str = "HelloWorld";

Pointers as Function Argument

Example: 

#include <stdio.h>

void swap(int *a, int *b);

int main()

{

    int x = 10, y = 20;

    printf("x = %d\n", x);

    printf("y = %d\n\n", y);

    swap(&x, &y);                //passing address 

    printf("After Swapping:\n\n");

    printf("x = %d\n", x);

    printf("y = %d", y);

return 0;

}

void swap(int *a, int *b)

{

    int t;

    t = *a;

   *a = *b;

b = t;

}