public class CaesarCipher {
    public static void main(String[] strings) {
        int offset = 0;
        char c;
        int shift= 0;;
        boolean isComplete = false;

        while (offset<=-25 || offset == 0  || offset >=25 || offset!=-999 || offset!=999) {
            TextIO.putln("Please enter the shift value (between -25..-1 and 1..25)");
            offset = TextIO.getlnInt();
            if (offset<=-25 || offset>=25 || offset == 0) {
                TextIO.putln(offset+" is not a valid shift value.");
            };
        }

        TextIO.putln("Using shift value of "+offset);

        while (isComplete == false) {
            TextIO.putln("Please enter the source text (empty line to quit)");
            String m= TextIO.getln();

            if (m.equals("")) {
                TextIO.putln("Bye.");
                isComplete =true;
                return;
            }

            TextIO.putln("Source   :"+m);
            m = m.toUpperCase();
            String result ="";

            if (offset == 999) {
                boolean posishift = true;
                offset = 1;
            }

            if (offset == -999) {
                boolean negashift = true;
                offset = -1;
            }

            for (int i=0; i<=m.length() -1; i++ )   {
                c = m.charAt(i);

                if (  (int)c >=65 && (int)c <=90)   {
                    int letter = c - 'A';
                    shift = (26 + letter + offset) % 26;
                    char newletter = (char) (shift + 'A');
                    result += newletter;
                }
                if (posishift) offset ++;
                if (negashift) offset --; else result += c;
            }

            TextIO.putln("Processed:"+result);

        }
    }

}