Caesar Cipher Code Flaw

Question

I have coded a Caesar cipher that seem to work in most tests but fails on a few cases. More on the test details are https://www.hackerrank.com/challenges/caesar-cipher-1

Basic info: The cipher only encrypts letters, symbols etc stay unencrypted.

Fails on this case:

90
!m-rB`-oN!.W`cLAcVbN/CqSoolII!SImji.!w/`Xu`uZa1TWPRq`uRBtok`xPT`lL-zPTc.BSRIhu..-!.!tcl!-U
62

Where 90 is n (characters in string), second line is string in array s, and 62 is k (amount of letter rotations)

Any insight into the flaw of my code will be highly appreciated

Code:

int main(){
int n;
scanf("%d",&n);
char* s = (char *)malloc(10240 * sizeof(char));
scanf("%s",s);
int k;
scanf("%d",&k);

if (k>26) {
    k%=26;
}

int rotation;
for(int i = 0; i<n; i++) {
    if (s[i] >= 'a' && s[i] <= 'z') {
        if((s[i] + k) > 'z' ) {
            rotation = (s[i] - 26) + k;
            s[i] = rotation;
        } else {
            s[i] = s[i]+k;
        }

    } else if (s[i] >= 'A' && s[i] <= 'Z') {
        if((s[i] + k) >= 'Z' ) {
            rotation = (s[i] - 26) + k;
            s[i] = rotation;
        } else {
            s[i] = s[i]+k;
        }
    } 

}

for(int i=0; i<n; i++) {
    printf("%c", s[i]);
}

return 0;
}

Answer 1

Ok guys, so I've figured it out.

Old Code:
 if((s[i] + k) >= 'Z' )
New Code:
 if((s[i] + k) > 'Z' )

It messed up when given a P(ascii 80), it should have stopped at Z(ascii 90) but instead did this calculation:

s[i] - 26 + k  = 64
  80 - 26 + 10 = 64 (ascii for @) and thus '@' was returned instead of Z