c - Caesar's Cipher Code

Question

#include <stdio.h>

void caesar (char cipher[], int shift);

int main () {

char cipher[50];
int shift;

  printf("Enter text to be encrypted IN CAPITAL LETTERS ONLY: ");
  scanf("%s", cipher);

  printf("How many shifts do you prefer? 1-10 only: ");
  scanf("%d", &shift);

  caesar (cipher, shift);

  return 0;
}

void caesar (char cipher[], int shift) {
  int i = 0;

  while (cipher[i] != '') {
    if ((cipher[i] += shift) >= 65 && (cipher[i] += shift) <= 90) {
      cipher[i] += (shift);
    } else {
      cipher[i] += (shift - 25); 
    }
    i++;
  }
  printf("%s", cipher);
}

I'm starting to get encrypted outputs but i'm afraid there's something wrong with my statements.

For Example:

• Input: ABCD, 1 shift
• Output: DEFG <= which is actually 3 shifts.

Answer 1

Change

if ((cipher[i] += shift) >= 65 && (cipher[i] += shift) <= 90) ...

to

if ((cipher[i] + shift) >= 65 && (cipher[i] + shift) <= 90) ...

since += modifies cipher[i].