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.

Code:

---

int main()
int crypt;
int x,y;
int key;
char input;

---

since when the main has such strange number of parameters?

it should be

Code:

---

int main(void)
{
  int crypt;
  int x,y;
  int key;
  char input;
  etc...

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fflush(stdin); - undefined - read FAQ

crypt=1 - this is assignment you want crypt==1