Assignment Project 4 and Calculator

Code

                        /// Name: Graham Pollock
                        /// Period: 5
                        /// Program Name: Calculator
                        /// File Name: Calculator.java
                        /// Date Finished: 04/10/2016/

    import java.util.Scanner;
    
    public class Calculator
    {
        public static void main(String[] args)
        {
            Scanner kb = new Scanner (System.in);
            
            double a, b, c;
            
            String op;
            
            do 
            {
                System.out.print("> ");
                a = kb.nextDouble();
                op = kb.next();
                b = kb.nextDouble();
                
                if (op.equals("+"))
                    c = add(a, b);
                else if (op.equals("-"))
                    c = subtract(a, b);
                else if (op.equals("*"))
                    c = multi(a, b);
                else if (op.equals("/"))
                    c = divide(a, b);
                else if (op.equals("%"))
                    c = modulus(a, b);
                else if (op.equals("!"))
                    c = fact(a);
                else if (op.equals("^"))
                    c = exp(a, b);
                else
                {
                    System.out.println("The operation '" + op + "' is not valid.");
                    c = 0;
                }
                
                if (a != 0)
                    System.out.println(c);
            } while (a != 0);
            
            System.out.println("Bye, now");
        }
        
        public static double add(double a, double b)
        {
            double total;
            
            total = a + b;
            
            return total;
        }
        
        public static double subtract(double a, double b)
        {
            double total;
            
            total = a - b;
            
            return total;
        }
        
        public static double multi(double a, double b)
        {
            double total;
            
            total = a * b;
            
            return total;
        }
        
        public static double divide(double a, double b)
        {
            double total;
            
            total = a / b;
            
            return total;
        }
        
        public static double modulus(double a, double b)
        {
            double total;
            
            total = a % b;
            
            return total;
        }
        
        public static double fact(double a)
        {
            double total = a;
            
            double z = a - 1;
            
            for (double n = z; n > 0; n--)
            {
                total = total * n;
            }
            
            return total;
        }
        
        public static double exp(double a, double b)
        {
            double total = a;
            
            for (int n = 1; n < b; n++)
            {
                total = total * a;
            }
            
            return total;
        }
    }  
    

Picture of the output