Chapter 3 Exercise 13, Introduction to Java Programming, Tenth Edition Y. Daniel LiangY.

*4.13 (Vowel or consonant?) Write a program that prompts the user to enter a letter and check whether the letter is a vowel or consonant. Here is a sample run:

    Enter a letter: B
    B is a consonant
    Enter a letter grade: a
    a is a vowel
    Enter a letter grade: #
    # is an invalid input 

import java.util.Scanner;
 
public class ProgrammingEx4_13 {
 
 public static void main(String[] args) {
  Scanner input = new Scanner(System.in);
  System.out.print("Enter a letter: ");
  String s = input.nextLine();
 
  // Check if the string has exactly one character
  if (s.length() != 1) {
   System.out.println("You must enter exactly one character");
   System.exit(1);
  }
 
  // Check if input is valid
  char ch = Character.toUpperCase(s.charAt(0));
  if (ch > 'Z' || ch < 'A') {
   System.out.println(s + " is an invalid input");
   System.exit(1);
  }
 
  if (ch == 'A' || ch == 'E' || ch == 'I' || ch == 'O' || ch == 'U') {
   System.out.println(s + " is a vowel");
   System.exit(1);
  }
  System.out.println(s + " is a consonant");
 
 }
 
}