Thread: Put this algorithm into code

I am trying to put this algorithm into code for my autokey cipher program.

If (keyIsNotExhaust) Encryption = currChar + key; else Encryption = currChar + prevChar;

If (keyIsNotExhaust) decryption = currChar - key; else decryption = currChar - decryption;

This is the code I have so far:

Code:

#include <stdio.h>

Code:

#include<string.h>
#include<stdlib.h>
#include<ctype.h>
#include<math.h>


char key[100];


unsigned int easyendecrypt(char c);


int main(void) {
    int c;
    while ((c = getc(stdin)) !=EOF) {
        putc(easyendecrypt(c), stdout);
    }
    printf("\n");
    return 0;
}


unsigned int easyendecrypt(char c) {
    char k;

#ifdef DECRYPT
    fprintf(stderr, "decrypting with %s\n",key);
    k = 'A' + (c - key);
    key[c] = k;
    return k;
#else
    fprintf(stderr,"encrypting with %s\n",key);
    k = key + (c + key - 2 * 'A');
    key[c]='\0';
    return k;
#endif
}