perl encode.pl -e

perl encode.pl -d

#!/usr/bin/perl
use warnings;

#if the version of perl you are using is older than
#5.6, then get rid of the line "use warning;" and
#make the first line look like this: #!/usr/bin/perl -w

#array used for encoding and decoding
@code = ("A".."Z", "a".."z"," ",0..9);
$eString = "";
$index = 0;

#setting the shift
print "Enter shift => ";
chop($shift = <STDIN>);

if ($ARGV[0] =~ /[Ee]/) {
		
	print "Enter a word => ";
	#getting input and removing newline char.
	chop ($word = <STDIN>);
	
	$eString = &shifter ($word, '+');

	#writing encoded word to file
	open(OUTFILE, ">encode.txt");
	print OUTFILE ($eString."\n");
	close(OUTFILE);

} elsif ($ARGV[0] =~ /[Dd]/) {

	unless (open(INFILE, "encode.txt")){
		die("Cannot open the file encode.txt");
	}
	#reading line from file
	$word = <INFILE>;
	close(INFILE);
	
	$eString = &shifter ($word, '-');
	
	print $eString."\n";
} 

sub shifter {
	my ($word, $direction) = @_;
	
	#making the string to an array, w/ one char per index
	@wordA = split(//, $word);

	#generating the encoded string
	for (1..length($word)){
		for ($i = 0; $i < @code; ++$i){
 			if ($wordA[$index] eq $code[$i]){
				if($direction eq '+'){
					$eString .= $code[$i+$shift];
				} else {
					$eString .= $code[$i-$shift];
				}
			}
		}
		$index++;
	}
	return $eString;
}

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

void encode(char *p, int key)
{
   if(*p>='a'&&*p<='z')
   {
      if(*p+key>'z') *p=*p+key-'z'+'0';
      else *p=*p+key;
   }else if(*p>='A' && *p<='Z')
      if(*p+key>'Z') *p=*p+key-'Z'+'a';
      else *p=*p+key;
   }else if(*p>='0' && *p<='9')
      if(*p+key>'9') *p=*p+key-'9'+'A';
      else *p=*p+key;
   }
}

void decode(char *p, int key)
{
   if(*p>='a'&&*p<='z')
   {
      if(*p-key<'a') *p=*p-key-'a'+'Z';
      else *p=*p-key;
   }else if(*p>='A' && *p<='Z')
      if(*p+key<'A') *p=*p-key-'A'+'9';
      else *p=*p+key;
   }else if(*p>='0' && *p<='9')
      if(*p+key<'0') *p=*p-key-'0'+'z';
      else *p=*p+key;
   }
}
int main(int argc, char *argv[])
{
   int key=3; /* Default encoding/decoding key */
   char *string, *p1, mode;
   
   if(argc<3 || argv[1][0] != '-') {printf("Usage: %s [flag] [string]\nFlags: -e Encode [string]\n-d Decode [string]", argv[0]); exit(EXIT_FAILURE);

   mode=argv[1][1];

   if(argc==4) key=atoi(argv[3]);
   strcpy(string, argv[2]);
 
   for(p1=string; *p1; p1++)
      if(mode=='e') encode(p1, key);
      else if(mode=='d') decode(p1, key);
      else{printf("Invalid mode\n"); exit(EXIT_FAILURE);}

   printf("%s\n", string);
}

#include <stdio.h>
#include <string.h>

int main()
{

  char mode;
  char c;
  char input[500];
  char output[500];
  int i = 0;
  int key;

  puts("Enter your message:");
  
  while( ( c = getchar() ) != '\n' )
  {
    input[i++] = c;
  }

  input[i] = '\0';

  printf("Do you want to [D]ecode or [E]ncode: ");
  scanf("%c", &mode);
  
  if ( mode == 'D' )
  {
    printf("Enter your key: ");
    scanf("%i", &key);
    /* Subtract key from each index. */
    int count = 0;
    int length = strlen(input);
    while( count <= length - 1 )
    {
      char temp = input[count];
      temp -= key;
      output[count] = temp;
      count++;
    }
    output[count] = '\0';
  }
  
  if ( mode == 'E' )
  {
    printf("Enter your key: ");
    scanf("%i", &key);
    /* Add key from each index */
    int length = strlen(input);
    int count = 0;
    while( count <= length )
    {
      char temp = input[count];
      temp += key;
      output[count] = temp;
      count++;  
    }
    output[count] = '\0';
  }

  puts("");   
  puts("Your input was:");
  puts(input);
  puts(""); 
  printf("Your key was: %i\n",key);
  puts("");
  puts("Your request has produced:");
  puts(output);

  return 0;
}