Caesar Cipher C程序未正确加密

Question

I've written a Caesar Cipher program for my class on C, and it doesn't seem to be encrypting correctly. The program takes input from a sentence "THE QUICK BROWN FOX JUMPS OVER THE LAZY DOG" and encrypts it using the Caesar Cipher method taking an enckey from the keyboard input. When it encrypts it, it does not do it correctly, and it decrypts it into nonsense. I looked over it and cannot figure out where I messed up to why it isn't encrypting the sentence in the proper way.

Here's the code:

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


int  Caesar_encrypt(char *p, char *s, int enckey);
int  Caesar_decrypt(char *p, char *s, int enckey);

int main(void){
  char A[]="THE QUICK BROWN FOX JUMPS OVER THE LAZY DOG";
  char B[50], /* stores encrypted output string  */
  C[50];  /* stores decrypted output using string B as source */
  int enckey,
  statuse, statusd; /* they store return values from the functions */

  printf("Plaintext for encryption is : %s \n", A);

  printf("Input numerical key for Caesar's cypher : ");
  scanf("%d",&enckey);
  putchar('\n');
  printf("You entered encryption key %d \n", enckey);

  /* encrypt by Caesar's cypher */
  statuse= Caesar_encrypt( A, B, enckey);

  printf("Ciphertext is : %s \n", B);

 /* decrypt by Caesar's cypher */
  statusd = Caesar_decrypt( B, C, enckey);
  printf("Decrypted text is: %s \n", C); 


  exit (0);
}

int  Caesar_encrypt(char *p, char *s, int enckey){
    *s = ((*p + enckey)%26) + 65 ;
    return 0;
}

int Caesar_decrypt(char *p, char *s, int enckey){
    *s = ((*p - enckey)%26) + 65 ;
    return 0;
}

If you could help me in anyway that would be great

Thanks for your time.

Answer 1

You are en/decrypting only the first character of the string. You must loop through all characters of the string.

And there is a problem with the en/decryption of the SPACE character. I leave this as an exercise for you.

Answer 2

#include <ctype.h>

int  Caesar_encrypt(char *p, char *s, int enckey){
    for(; *p ; ++s, ++p){
        *s = isupper(*p) ? (*p - 'A' + enckey)%26 + 'A' : *p;
    }
    *s = '\0';
    return 0;//?
}

int Caesar_decrypt(char *p, char *s, int enckey){
    for(; *p ; ++s, ++p){
        *s = isupper(*p) ? (*p - 'A' + (26-enckey))%26 + 'A' : *p;
    }
    *s = '\0';
    return 0;//?
}