CS50 Caesar. invisible characters printing after upper case letters - c

Question

I've written the below code for the Caesar project in CS50 and I felt like it was hitting the brief, but when I have run the check, both of the checks containing uppercase letters are coming back incorrect There seems to be some extra characters printed between each of the uppercase letters that don't appear when I run the code myself.
Am I missing something in my code that's causing this to happen?
the message from Check50
:( encrypts "BARFOO" as "EDUIRR" using 3 as key
expected "ciphertext: ED...", not "ciphertext: E\..."
:( encrypts "BaRFoo" as "FeVJss" using 4 as key
expected "ciphertext: Fe...", not "ciphertext: F\..."
my code
#include <cs50.h>
#include <stdio.h>
#include <ctype.h>
#include <stdlib.h>
#include <string.h>
bool only_digits(string s);
char rotate(int, int);
int main(int argc, string argv[])
{
//make sure key is entered correctly
{
if (argc != 2)
{
printf("Usage: ./caesar key\n");
return 1;
}
else
{
int cont = only_digits(argv[1]);
if (cont != 1)
{
return 1;
}
else
{
// convert key from string to int
int key = atoi(argv[1]);
string plain = get_string("plain text: \n");
// rotate the letters using the key
printf("ciphertext: ");
{
for (int i = 0, len = strlen(plain); i < len; i++)
{
rotate(plain[i], key);
}
}
printf("\n");
}
}
}
}
//rotate the letters using the key
char rotate(int p, int i)
{
// rotate uppers
if isupper(p)
{
p = p - 65;
char c = (p + i) % 26;
c += 65;
printf("%c", c);
}
// rotate lowers
if islower(p)
{
p = p - 97;
char c = (p + i) % 26;
c += 97;
printf("%c", c);
}
// if its a character keep the same
else
{
printf("%c", p);
}
return 0;
}
//make sure key entered is only digits
bool only_digits(string s)
{
for (int i = 0, len = strlen(s); i < len; i++)
{
if (!isdigit(s[i]))
{
printf("Usage: ./caesar key\n");
return 0;
}
else
{
;
}
}
return 1;
}

Answer 1

While I am unsure if it's your only bug, you forgot an else if in your rotate function such that upper case letters would print in the first case but also the else to the second case after they had been modified.
char rotate(int p, int i)
{
// rotate uppers
if isupper(p)
{
p = p - 65;
char c = (p + i) % 26;
c += 65;
printf("%c", c);
}
// rotate lowers
else if islower(p) // without else if here, upper cases would fall into the else below with p - 65
{
p = p - 97;
char c = (p + i) % 26;
c += 97;
printf("%c", c);
}
// if its a character keep the same
else
{
printf("%c", p);
}
return 0;
}