Thread: Caesar Cipher

I need to make an encrypt/decrypt Caesar algorithm that asks for the user to put in a key. The following is what I have so far, I started off doing a rot-13 and tried to progress but as you can see, ran into a couple of problems. It is not complete yet because I have to ask for character input, but I'm having trouble seeing where I need to add a string array. Can anyone point me in the right direction and maybe give me a hint on what to do? Thanks.

Code:

#include<stdio.h>


int main()
int crypt;
int x,y;
int key;
char input;
{
	printf("Do you want your characters encrypted [1] or decrypted [2]? \n");
	scanf("%d", crypt);
	printf("Enter a key");
	scanf("%d", key);

    while((x=getchar())!=EOF && crypt=1)
	{
		printf("Enter data to encrypt.\n");
		fflush(stdin);
    	gets(input);
		if(x >='A' && x <='Z')
		{
			if((y = x + key) <= 'Z')
				putchar(y);
			else
			{
				   y = x - key;
				putchar(y);
			}
		}
		else if(x >='a' && x <='z')
		{
			if((y= x + key) <= 'z')
				putchar(y);
			else
			{
				y = x - key;
				putchar(y);
			}
		}
		else
			putchar(x);
	}

return 0;
}

Since there is no such thing as a string array, adding one will be very difficult.

So in your input thing, you can read a character at a time if you want, there's nothing stopping you. If you want to read in a line at a time, then make input an array of char instead of just a single char.

And there is no correct way to use gets.

You need to learn about scanf.

Code:

  scanf("%d", &digit);

  scanf("%c", &char);

  scanf("%s", char array);

The ampersand char in C means "the address of". Since array names ARE their address, they don't
need an ampersand before them when in scanf().


That should help.

So, does that mean my variables are okay? I'm really confused now because I missed the class my teacher went over character arrays and the book is not helping much. I think the "gets" thing was a typo my teacher made, but he said we needed that to scan for a whole line and not just the first word.

You would then need to make x travel through each character in the input array. You would also need to encrypt using a caesar cipher correctly. (Hint: y = x - key is not using a caesar cipher correctly.)

Would it not be faster to have something like:

Example:

Code:

static unsigned char ascii[256];

int init(int seed)
{
  register unsigned char *s = ascii, uc_seed = (unsigned char)seed;
  register const unsigned char *end = ascii + sizeof(ascii);

  for(;s < end;)
    *s++ = uc_seed++;
}

Then you would simply just encode by saying ascii[letter_you_wish_to_encode].

Except for "punctuation doesn't change" and "arithmetic mod 26" parts.

Oh well, I guess this is what happens when you only deal with me when it is the end of the day and I am tired.