To reverse the first n characters in a file

Description:

                  This program perform the reverse operation of  n characters in the file

Algorithm:

Step 1: Star

Step 2: read the command line arguments

Step 3: check if arguments=3 or not

                           If not print invalid no of arguments

Step 4: open source file in read mode

Step 5: if NULL pointer, then print file can not be open

Step 6: Store no of chars to reverse in k

                     K= *argv[2]-48

Step 7: read the item from file stream using fread

Step 8: Store chars from last position to initial position in another string(temp)

Step 9: print the temp string

Step 10: Stop

Program:

#include <stdio.h>

#include <conio.h>

#include <string.h>

#include <process.h>

void main(int argc, char *argv[])

{

  char a[15];

  char s[20];

  char n;

  int k;

  int j=0;

  int i;

  int len;

  FILE *fp;

  if(argc!=3)

  {

            puts("Improper number of arguments.");

             exit(0);

  }

  fp = fopen(argv[1],"r");

  if(fp == NULL)

  {

  puts("File cannot be opened.");

  exit(0);

  }

  k=*argv[2]-48;

  n = fread(a,1,k,fp);

  a[n]='\0';

  len=strlen(a);

  for(i=len-1;i>=0;i--)

  {

              s[j]=a[i];

             printf("%c",s[j]);

              j=j+1;

}

s[j+1]='\0';

getch();

}

Output:

source.c

           this is source

ouput.c

Command line arguments

source.c ouput.c

source.c

           this is source

           ecruos si siht

Command line arguments

source.c

Invalid number of arguments.

Conclusion: the program is error free

VIVA QUESATIONS:

1) List out the file handling functions ?

Ans: fopen(), fprintf(),fclose(),fscanf(),fgetc(),fputc(), etc..,

2) What is the use of  fseek() function ?

Ans: The function fseek sets the file pointer associated with a stream to a new position

3) What is use of the fflush() function ?

Ans:  If the given stream has a buffered output, fflush writes the output of the stream to the associate file.