Programming Tutorial

Kerala University Btech First & Second Semester Exam result 2011

2011-11-11T07:47:00.000-08:00

Kerala University btech Combined 1st & 2nd Semester 2011 Exam Result will Published on 14-11-2011.

To view results go to

http://www.keralauniversity.edu/

File Handling in C

2011-11-03T06:18:00.000-07:00

We frequently use files for storing information which can be processed by our programs. In order to store information permanently and retrieve it we need to use files.

Files are not only used for data. Our programs are also stored in files.

The editor which you use to enter your program and save it, simply manipulates files for you.

The Unix commands cat, cp, cmp are all programs which process your files.

In order to use files we have to learn about File I/O i.e. how to write information to a file and how to read information from a file.

We will see that file I/O is almost identical to the terminal I/O that we have being using so far.

The primary difference between manipulating files and doing terminal I/O is that we must specify in our programs which files we wish to use.

As you know, you can have many files on your disk. If you wish to use a file in your programs, then you must specify which file or files you wish to use.

Specifying the file you wish to use is referred to as opening the file.

When you open a file you must also specify what you wish to do with it i.e. Read from the file, Write to the file, or both.

Because you may use a number of different files in your program, you must specify when reading or writing which file you wish to use. This is accomplished by using a variable called a file pointer.

Every file you open has its own file pointer variable. When you wish to write to a file you specify the file by using its file pointer variable.

You declare these file pointer variables as follows:

FILE *fopen(), *fp1, *fp2, *fp3;

The variables fp1, fp2, fp3 are file pointers. You may use any name you wish.

The file <stdio.h> contains declarations for the Standard I/O library and should always be included at the very beginning of C programs using files.

Constants such as FILE, EOF and NULL are defined in <stdio.h>.

You should note that a file pointer is simply a variable like an integer or character.

It does not point to a file or the data in a file. It is simply used to indicate which file your I/O operation refers to.

A file number is used in the Basic language and a unit number is used in Fortran for the same purpose.

The function fopen is one of the Standard Library functions and returns a file pointer which you use to refer to the file you have opened e.g.

fp = fopen( “prog.c”, “r”) ;

The above statement opens a file called prog.c for reading and associates the file pointer fp with the file.

When we wish to access this file for I/O, we use the file pointer variable fp to refer to it.

You can have up to about 20 files open in your program - you need one file pointer for each file you intend to use.

File I/O

The Standard I/O Library provides similar routines for file I/O to those used for standard I/O.

The routine getc(fp) is similar to getchar()

and putc(c,fp) is similar to putchar(c).

Thus the statement

c = getc(fp);

reads the next character from the file referenced by fp and the statement

putc(c,fp);

writes the character c into file referenced by fp.

/* file.c: Display contents of a file on screen */

#include <stdio.h>

void main()

{

FILE *fopen(), *fp;

int c ;

fp = fopen( “prog.c”, “r” );

c = getc( fp ) ;

while ( c != EOF )

{

putchar( c );

c = getc ( fp );

}

fclose( fp );

}

In this program, we open the file prog.c for reading.

We then read a character from the file. This file must exist for this program to work.

If the file is empty, we are at the end, so getc returns EOF a special value to indicate that the end of file has been reached. (Normally -1 is used for EOF)

The while loop simply keeps reading characters from the file and displaying them, until the end of the file is reached.

The function fclose is used to close the file i.e. indicate that we are finished processing this file.

We could reuse the file pointer fp by opening another file.

This program is in effect a special purpose cat command. It displays file contents on the screen, but only for a file called prog.c.

By allowing the user enter a file name, which would be stored in a string, we can modify the above to make it an interactive cat command:

/* cat2.c: Prompt user for filename and display file on screen */

#include <stdio.h>

void main()

{

FILE *fopen(), *fp;

int c ;

char filename[40] ;

printf(“Enter file to be displayed: “);

gets( filename ) ;

fp = fopen( filename, “r”);

c = getc( fp ) ;

while ( c != EOF )

{

putchar(c);

c = getc ( fp );

}

fclose( fp );

}

In this program, we pass the name of the file to be opened which is stored in the array called filename, to the fopen function. In general, anywhere a string constant such as “prog,c” can be used so can a character array such as filename. (Note the reverse is not true).

The above programs suffer a major limitation. They do not check whether the files to be used exist or not.

If you attempt to read from an non-existent file, your program will crash!!

The fopen function was designed to cope with this eventuality. It checks if the file can be opened appropriately. If the file cannot be opened, it returns a NULL pointer. Thus by checking the file pointer returned by fopen, you can determine if the file was opened correctly and take appropriate action e.g.

fp = fopen (filename, “r”) ;

if ( fp == NULL)

{

printf(“Cannot open %s for reading \n”, filename );

exit(1) ; /*Terminate program: Commit suicide !!*/

}

The above code fragment show how a program might check if a file could be opened appropriately.

The function exit() is a special function which terminates your program immediately.

exit(0) mean that you wish to indicate that your program terminated successfully whereas a nonzero value means that your program is terminating due to an error condition.

Alternatively, you could prompt the user to enter the filename again, and try to open it again:

fp = fopen (fname, “r”) ;

while ( fp == NULL)

{

printf(“Cannot open %s for reading \n”, fname );

printf(“\n\nEnter filename :” );

gets( fname );

fp = fopen (fname, “r”) ;

}

In this code fragment, we keep reading filenames from the user until a valid existing filename is entered.

Exercise: Modify the above code fragment to allow the user 3 chances to enter a valid filename. If a valid file name is not entered after 3 chances, terminate the program.

RULE: Always check when opening files, that fopen succeeds in opening the files appropriately.

Obeying this simple rule will save you much headache.

Example 1: Write a program to count the number of lines and characters in a file.

Note: Each line of input from a file or keyboard will be terminated by the newline character ‘\n’. Thus by counting newlines we know how many lines there are in our input.

/*count.c : Count characters in a file*/

#include <stdio.h>

void main()

/* Prompt user for file and count number of characters

and lines in it*/

{

FILE *fopen(), *fp;

int c , nc, nlines;

char filename[40] ;

nlines = 0 ;

nc = 0;

printf(“Enter file name: “);

gets( filename );

fp = fopen( filename, “r” );

if ( fp == NULL )

{

printf(“Cannot open %s for reading \n”, filename );

exit(1); /* terminate program */

}

c = getc( fp ) ;

while ( c != EOF )

{

if ( c == ‘\n’ )

nlines++ ;

nc++ ;

c = getc ( fp );

}

fclose( fp );

if ( nc != 0 )

{

printf(“There are %d characters in %s \n”, nc, filename );

printf(“There are %d lines \n”, nlines );

}

else

printf(“File: %s is empty \n”, filename );

}

Example 2: Write a program to display file contents 20 lines at a time. The program pauses after displaying 20 lines until the user presses either Q to quit or Return to display the next 20 lines. (The Unix operating system has a command called more to do this ) As in previous programs, we read the filename from user and open it appropriately. We then process the file:

read character from file

while not end of file and not finished do

begin

display character

if character is newline then

linecount = linecount + 1;

if linecount == 20 then

begin

linecount = 1 ;

Prompt user and get reply;

end

Close files

The step: “Read characters .... and write ..” may be refined to:

read character from prog.c

while not end of file do

begin

write character to prog.old

Program to delete duplicate elements in an array

2011-10-31T00:34:00.000-07:00

#include<stdio.h>
int main(){
int arr[50];
int *p;
int i,j,k,size,n;
printf("\nEnter size of the array: ");
scanf("%d",&n);
printf("\nEnter %d elements into the array: ",n);
for(i=0;i<n;i++)
scanf("%d",&arr[i]);
size=n;
p=arr;
for(i=0;i<size;i++){
for(j=0;j<size;j++){
if(i==j){
continue;
}
else if(*(p+i)==*(p+j)){
k=j;
size--;
while(k < size){
*(p+k)=*(p+k+1);
k++;
}
j=0;
}
}
}
printf("\nThe array after removing duplicates is: ");
for(i=0;i < size;i++){
printf(" %d",arr[i]);
}
return 0;
}

Program to concatenate two strings without using string functions

2011-10-31T00:33:00.000-07:00

#include<stdio.h>
#include<conio.h>
void main()
{
char a[50],b[50];
int i,j,n,k;
clrscr();
printf("\n Please Give The STRING OF A : ");
scanf("%s",a);
printf("\n Please Give The STRING OF B : ");
scanf("%s",b);
for(i=0,k=0;a[i]!='\0';i++)
k++;
for(j=0,n=0;b[j]!='\0';j++)
n++;
printf("VALUE OF K=%d",k);
printf("VALUE OF N=%d",n);
for(i=k,j=0;i<=n+k;i++,j++)
a[i]=b[j];

printf("\n THE Concatenated string is %s .",a);
getch();
}

Program to sort an array using bubble sort

2011-10-31T00:29:00.001-07:00

#include<stdio.h>
main()
{
int n,i,j,temp;
printf("Enter the number of elements: ");
scanf("%d",&n);
int a[n];
printf("Enter the elements in the array\n");
for(i=0;i<n;i++)
scanf("%d",&a[i]);
for(i=0;i<n;i++)
{
for(j=i+1;j<n;j++)
{
if(a[i]>a[j])
{
temp=a[i];
a[i]=a[j];
a[j]=temp;
}
}
}
printf("\nThe sorted array is - \n" );
for(i=0;i<n;i++)
printf("%d, ",a[i]);
}

Program to count number of sentences words and letters in a paragraph

2011-10-31T00:28:00.000-07:00

#include<stdio.h>
main()
{
char ch[150];
int i,c=0,c1=0,c2=0;
printf("Enter a Paragraph \n");
gets(ch);
for(i=0;ch[i]!='\0';i++)
{
if(ch[i]=='.'||ch[i]=='!'||ch[i]=='?')
{ c++;
c1++;
}
else if(ch[i]==' '||ch[i]==',')
c1++;
else if(ch[i]>65&&ch[i]<123)
c2++;
}
printf("\nNumber of letters = %d \nNumber of words=%d ",c2,c1);
printf("\nNumber of Sentences = %d\n",c);
}

Program to search an element using linear search or binary search (menu driven program)

2011-10-31T00:27:00.000-07:00

#include<stdio.h>
void main()
{
int a[25],beg,item,last,n,num,i,ch,mid,f=0;
printf("menu\n");
printf("\n 1.linear search");
printf("\n 2.binary search");
printf("\n enter the choice");
scanf("%d",&ch);
if(ch==1)
{
printf("\n enter the number of elements in the array");
scanf("%d",&n);
printf("\n enter the sorted array");
for(i=0;i<n;i++)
scanf("%d",&a[i]);
printf("\n enter the item to be searched");
scanf("%d",&item);
for(i=0;i<n;i++)
{
if(a[i]==item)
{
printf("\n item found at position%d",i+1);
break;
}
}
if(i==n)
printf("\n item not found");
}
if(ch==2)
{
printf("\nenter the number of elements in the array");
scanf("%d",&n);
printf("enter the sorted array");
for(i=0;i<n;i++)
scanf("%d",&a[i]);
printf("item to be searched");
scanf("%d",&item);
last=n-1;
mid=(beg+last)/2;
while(beg<=last)
{
if(item==a[mid])
{
printf("\n item found at position %d",mid+1);
break;
}
else if(a[mid]>item)
last=mid-1;
else beg=mid+1;
mid=(beg+last)/2;
}
}
}

Program to convert a string to upper case

2011-10-31T00:25:00.000-07:00

#include<stdio.h>
#include<string.h>
main()
{
char s[50];
int i,l;
printf("Enter some text: ");
gets(s);
l=strlen(s);
for(i=0;i<l;i++)
{
if(s[i]>='a'&&s[i]<='z')
s[i]-=32;
}
printf("Text after converting to upper case: ");
puts(s);
}

Program to copy a file to another file

2011-10-31T00:24:00.000-07:00

#include<stdio.h>
void main()
{
FILE *fp1,*fp2;
char ch;
char fname1[30],fname2[30];
printf("Enter the source file: ");
fflush(stdin);
scanf("%s",fname1);
printf("Enter the destination file: ");
fflush(stdin);
scanf("%s",fname2);
fp1=fopen(fname1,"r");
fp2=fopen(fname2,"w");
if(fp1==NULL)
{
printf("\n cannot open file %s for reading",fname1);
exit(1);
}
else if(fp2==NULL)
{
printf("\n cannot open file %s for writing",fname2);
exit(1);
}
else
{
ch=getc(fp1);
while(ch!=EOF)
{
putc(ch,fp2);
ch=getc(fp1);
}
fclose(fp1);
fclose(fp2);
printf("\n files copied");
}
}

Program to count vowels consonents and spaces in a string

2011-10-31T00:23:00.000-07:00

#include<stdio.h>
main()
{
int i,cons=0,vow=0,sp=0;
char a[100];
printf("Enter the sentence\n");
gets(a);
for(i=0;a[i]!='\0';i++)
{
if(a[i]=='a'||a[i]=='A')
vow=vow+1;
else if(a[i]=='e'||a[i]=='E')
vow=vow+1;
else if(a[i]=='i'||a[i]=='I')
vow=vow+1;
else if(a[i]=='o'||a[i]=='O')
vow=vow+1;
else if(a[i]=='u'||a[i]=='U')
vow=vow+1;
else if(a[i]==' ')
sp=sp+1;
else
cons=cons+1;
}
printf("Total number of vowels entered = %d\n",vow);
printf("Total number of consonents entered = %d\n",cons);
printf("Total number of spaces entered = %d\n",sp);
}

Program to find smallest in an array using pointer

2011-10-31T00:21:00.001-07:00

#include<stdio.h>

main()
{
int i,n;
printf("\nHow many elements?: ");
scanf("%d",&n);
int a[n];
for(i=0;i<n;i++)
{ printf("Element %d: ",i+1);
scanf("%d",&a[i]);
}
printf("\nCreating pointer now...");
int *p,small;
p = a;
small=*p;
i=1;
while(i<n)
{
if(small > *p)
small=*p;
i++;
p++;
}
printf("\nSmallest number: %d \n",small);
}

Program to merge and sort two arrays

2011-10-31T00:20:00.000-07:00

#include<stdio.h>
void sort(int a[],int);
void main()
{
int a[20],c[10],i,m,n,j;
printf("Enter the no.of elements in 1st array- \n");
scanf("%d",&m);
printf("Enter the 1st array - \n");
for(i=0;i<m;i++)
scanf("%d",&a[i]);
printf("Enter the no.of elements in the 2nd array");
scanf("%d",&n);
printf("Enter the 2nd array");
for(i=0;i<n;i++)
scanf("%d",&c[i]);
sort(a,m);
printf("1st sorted array - \n");
for(i=0;i<m;i++)
printf("%d, ",a[i]);
sort(c,n);
printf("2nd sorted array - \n");
for(i=0;i<n;i++)
printf("%d, ",c[i]);
j=m;
for(i=0;i<n;i++)
{a[j]=c[i];
j++;}
sort(a,m+n);
printf("Merged and Sorted array - \n");
for(i=0;i<m+n;i++)
printf("%d, ",a[i]);
}
void sort(int a[],int n)
{
int i,j,temp;
for(i=0;i<n;i++)
{ for(j=i+1;j<n;j++)
if(a[i]>a[j])
{ temp=a[i];
a[i]=a[j];
a[j]=temp;
}
}
}