few test cases are failing can someone point out the error.

    String temp="";
    for(int i=0;i<=s.length();i++)
    {
        if(s.charAt(i)-'a'>=0 && s.charAt(i)-'z'<26)
        {
            int te=(int)s.charAt(i)-97;
            te=(te+k)%26;
            temp=temp+(char)(te+97);
        } 
        else if(s.charAt(i)-'A'>=0 && s.charAt(i)-'Z'<26)
        {
            int tem=(int)s.charAt(i)-65;
            tem=(tem+k)%26;
            temp=temp+(char)(tem+65);

        }
        else
        {
            temp=temp+s.charAt(i);
        }
    }
    return(temp);