ANSWERS TO MORE PRACTICE PROBLEMS 

// Problem 1.
public static void main(String[] args)
{
    String s;
    char x;

    s = JOptionPane.showMessageDialog("Enter a string.");
    x = JOptionPane.showMessageDialog("Enter a letter.").charAt(0);

    if (s.length() == 0)
        System.out.println("String is length 0");
    else if(s.charAt(0) == x)
        System.out.println("First letter of string is " + x + ".");
    else
        System.out.println("First letter of string is not " + x + ".");
}

// Problem 2.
// To convert a digit char to an int, subtract 48 from its ascii code.
public static void main(String[] args)
{
    String s;
    int i, digit, sum = 0;

    s = JOptionPane.showMessageDialog("Enter an int.");
    for(i = 0; i < s.length(); i++)
    {
        digit = s.charAt(i) - 48;
        sum += digit; 
    }
    System.out.println("The sum of the digits is " + sum + ".");
}

// Problem 3.
public static void main(String[] args)
{
    int number, factor;
    boolean flag = true;
 
    number = JOptionPane.showMessageDialog("Enter a positive int.");
    for(factor = 2; factor <= number - 1; factor++)
        if (number % factor == 0)
            flag = false;

    if (flag)
        System.out.println("Prime")
    else
        System.out.println("Composite");
}

// Problem 4
public static void main(String[] args)
{
    int i, j;
    VendingMachine vm = new VendingMachine(10);
  
    for(j = 1; j <=4; j++)
    {
        for(i = 1; i <= 3; i++)
            vm.depositQuarter(); 
        vm.selectCandy();
    } 
    vm.printStatus();
}