Question

The question asks you to assume that your input file is an English text that may contain any character that appears on keyboard of a computer. The task is to read each character from the input file and after encrypting it by adding an integer value n (0 < n < 128) to the character, to write the encrypted character to output file.

We are supposed to use command line arguments and utilize argc, and argv parameters in main function of the code.

For example:

Command line arguments

       assign2 –e n infile outfile  

  or

      assign2 –d infile outfile  

The -e indicates that you would like to encrypt infile and write the result to outfile, while n indicates the number (0 < n < 128). The -d indicates that you want to decrypt infile (of course the file should have been encrypted) and write the result to outfile using the data from the infile.

Answer 1

Below is the code which does the job:

#include <stdio.h>
#include <stdlib.h>

void encrypt(int n, char fname[], char op_file[]){
   char ch; FILE *fpts, *fptt;
   fpts=fopen(fname, "r");
   if(fpts==NULL)
   {
       printf(" File does not exists or error in opening..!!");
       exit(1);
   }
   fptt=fopen(op_file, "w");
   if(fptt==NULL)
   {
       printf(" Error in creation of file temp.txt ..!!");
       fclose(fpts);
       exit(2);
   }
   while(1)
   {
       ch=fgetc(fpts);
       if(ch==EOF)
       {
           break;
       }
       else
       {
           ch=ch+n;
           fputc(ch, fptt);
       }
   }
   fclose(fpts);
   fclose(fptt);
   fpts=fopen(fname, "w");
   if(fpts==NULL)
   {
       printf(" File does not exists or error in opening..!!");
       exit(3);
   }
   fptt=fopen(op_file, "r");
   if(fptt==NULL)
   {
       printf(" File does not exists or error in opening..!!");
       fclose(fpts);
       exit(4);
   }
   while(1)
   {
       ch=fgetc(fptt);
       if(ch==EOF)
       {
           break;
       }
       else
       {
           fputc(ch, fpts);
       }
   }
   printf(" File %s successfully encrypted ..!!\n\n", fname);
   fclose(fpts);
   fclose(fptt);
}

void decrypt(char fname[], char op_file[]){
   char ch;
   FILE *fpts, *fptt;
  
   fpts=fopen(fname, "w");
   if(fpts==NULL)
   {
       printf(" File does not exists or error in opening..!!");
       exit(7);
   }
   fptt=fopen(op_file, "r");
   if(fptt==NULL)
   {
       printf(" File does not exists or error in opening..!!");
       fclose(fpts);
       exit(9);
   }
   while(1)
   {
       ch=fgetc(fptt);
       if(ch==EOF)
       {
           break;
       }
       else
       {
           ch=ch-100;
           fputc(ch, fpts);
       }
   }
   printf(" The file %s decrypted successfully..!!\n\n",fname);
   fclose(fpts);
   fclose(fptt);

}

void main(int argc, char *argv[])
{
   if( argc ==5){
       encrypt(atoi(argv[2]),argv[3],argv[4]);
   }
   else if(argc==4){
       decrypt(argv[2],argv[3]);
   }
   else if(argc > 5){
       printf("too many arguments provided\n");
   }
   else if(argc < 4){
       printf("few arguments provided\n");
   }
}