Thread: keyword replacement

also array1 is not null-terminated string - it is just a char array, you cannot use strlen on it.

It's much easier to write this

Code:

char aarray[]={'a','b','c','d','e','f','g','h','i','j','k','l','m','n','o','p','q','r','s','t','u','v','w','x','y','z',' '};

as this

Code:

char aarray[] = "abcdefghijklmnopqrstuvwxyz ";

and you get a NULL terminator in the second version, too.

Originally Posted by JackBear

Ive made a couple of changes to silly mistakes, but im still not getting any results.

Code:

char encodemessage()

{
char aarray[]={'a','b','c','d','e','f','g','h','i','j','k','l','m','n','o','p','q','r','s','t','u','v','w','x','y','z',' '};
char array1[]={'z','y','x','w','v','u','t','s','r','q','p','o','n','m','l','k','j','i','h','g','f','e','d','c','b','a',' '};

char key[333];
char newmessage[333];
int a;
int b;
b = strlen(array1);
int q;
int r;
r = strlen(message);
int x;
int y;
y = strlen(key);
int i;

	clrscr();
	printf("%s", message);
	printf("\nEnter key for cipher: ");
	gets(key);
	
	for(x=0;x<y;x++){
		
		for(a=0;a<b;a++){
			
			if(array1[a]==key[x]){
				array1[a]='*';		
			}
		}

	}				

	strcat(key, array1);


	for(q=0;q<r;q++){
		if(message[q]==aarray[i] && message[q]!=NULL aarray[i]!=NULL && array1[i]!=NULL && key[i]!=NULL){
				message[q]=key[i];	
		}
	
			else
				i++;
	}
				

		
strncpy(newmessage, message, q);
printf("\n\n\n%s", newmessage);
return 0;

Im trying to make a keyword replacement program. I want to be able to enter a keyword into the program which will then change move the letters of the alphabet around:

If the word cipher was used the alphabet would look like this:

abcdefghijklmnopqrstuvwxyz

cipherzyxwvutsqonmlkjgfdba

If my name was used the alphabet would look like this:

abcdefghijklmnopqrstuvwxyz

jackzyxwvutsrqponmlihgfedb

Below is a function ive made for encoding the a message that has been entered into the string message[333].

If anyone could give me some advice I would really appreciate it, Ive had a lot of sleepless nights with this one!

One more thing, this is an assignment set by my college and I dont want anyone to do my homework for me, im just looking for a bit of advice.

Thanks!
Jack

Hi Jack,
Looks like there are two main parts to your assignment's algorithm:

1) Take the letters from the added word, and print them first, in order.

Then

2) Take all the remaining letters, and print them in descending order (z - a)

#1 is obviously trivial, agreed?

#2 could be dealt with simply by using an array of 26 char's, with the letters of the alphabet (which you have) already.

Simple example: the input word is "abe", so we print:
abe

In the alphabet array, a is in alpha[0], because it's the first letter of the alphabet. So we set alpha[0] = 1, signifying that the a has already been used or printed. We do the same thing with alpha[1] or b, and alpha[4] or e. (a==0. b == 1, c==2,... e ==4)

Now, in a for loop (for instance), we scan through the alpha array. from the last element in the array, alpha[25], to alpha[0]. If the alpha [i] == 0, then we need to print the letter which corresponds to the subscript of alpha[i]. If the alpha[i] == 1, then we print nothing and go to the next lower letter.

The main thing is to keep it simple and clear as a bell. (And not use so many cliche's, but that's my problem)

Let me know if that makes sense to you or not. Don't worry about the syntax issues yet. Let's get the algorithm right, and then we'll flush out all the details.

As the letters are printed, they can simply be added into a second key [] array, in their proper order, from key[0] to key[25]. That's just a detail, really.

Adak

Jack, you're carrying on with a hardcoded key example, when your program needs a softcoded one, using logic that will not do what you want, (although I don't quite grok your algorithm, so who knows?).

You need to get your cipher[] (which is not a cipher, but a key, and the naming may confuse you and everyone else), working right, before trying to expand to the rest of your program. The cipher is the output from the product of the plaintext message and the key.
plaintext + key == ciphertext.

Once you get your algorithm right, then all the details can get nailed down.

Take some time, work it out by hand, and then write down your steps you're using to get it done. Big steps become functions, little steps go inside the big steps if they're a good functional fit.

I recommend a cull on your headers

Code:

#include <stdio.h>
#include <dos.h>
#include <math.h>
#include "bcio2.h"
#include <string.h>
#include <stdlib.h>
#include <conio.h>
#include <ctype.h>

The only ones your using are,

Code:

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

Also read the FAQ regarding main(), int main(), void main(). Although main() == int main(void) you should really ensure it is

Code:

int main(void)
{
/* ... */

Jack,
At some point in your steps you're going to want to "take all the letters not used int he portion of the key that was entered, and put them
backwards onto the end of the entered portion.

A good simple way to do that is to have a Used [] array of char's. All the letters will just fit in it, and so every char that gets used in the entered
portion of the key, will be recorded into the used array. Just a 0 (that letter wasn't used), or a 1 (it was used), is all it will hold.

Say the entered key was "key". Our used [] would look like this:

Code:

A B C D E F G H I J  K   L   M   N   O   P   Q   R   S   T   U   V   W   X   Y   Z -letters represented
0 1 2 3 4 5 6 7 8 9 10  11  12  13  14  15  16  17  18  19  20  21  22  23  24  25 - subscripts "
0 0 0 0 1 0 0 0 0 0  1   0   0   0   0   0   0   0   0   0   0   0   0   0   1   0  - value in array

You don't have to do it just this way, at all, but you do have to reach the same goal, in the end.

edit: Good catch Vart, we need the keyword to have the null char right after the last letter: '\0' .

edit 2: This was what I used for a final assignment into the key array,
(Not the key letters entered by the user, but all the other letters that the user didn't enter).

Code:

for (i = Size - 1, j - i; i >= 0; i--)  {
   if (used[i] == 0)  {
      key[j] = alpha[i];
      j--;
   }
}

IMO, the j variable makes this a pretty sly dog, indeed.

Note that as with any single alphabetic substitution, the key the user enters, can have no duplicates.

you are still using strlen on the not-null terminated array