encryptString function
Implementation
String encryptString(String input, int shift) {
final output = StringBuffer();
for (final char in input.runes) {
if (char >= 65 && char <= 90) {
output.write(String.fromCharCode((char - 65 + shift) % 26 + 65));
} else if (char >= 97 && char <= 122) {
output.write(String.fromCharCode((char - 97 + shift) % 26 + 97));
} else {
output.write(String.fromCharCode(char));
}
}
return output.toString();
}