Problem with capital letters in Pset2 Caesar's cipher

Question

My code encrypts the messages I enter; however, the capital letters are printed twice, first the ciphertext (which is correct) then the plaintext that was entered by the user (ex. "Hello" with a key of 3 prints as "KHhoor".) Why is that 'H' printing? Any help is much appreciated!

int key = atoi(argv[1]);
int i, n;
s = GetString();

for(i = 0, n = strlen(s); i < n; i++)
{
    if(isupper(s[i]))
    {
        printf("%c", (((s[i] + key - 'A') % 26) + 'A'));
    }
    if(islower(s[i]))
    {
        printf("%c", (((s[i] + key - 'a') % 26) + 'a'));
    }
    else
    {
        printf("%c", s[i]);
    }
}

Answer 1

It's your program structure. You are doing this:

if(x) do a;

if(y) do b; else do c;

A capital letter is represented as x. So, it does a. Then, since x is not y, it won't do b, but it will do c. Net, it does a and c. In your case, a and c are printf statements.

The else is only associated with the second if. The second if stands seperate from the first, and both if statements are assessed seperately. If you had done if / else if / else, it would probably be ok.

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