Project#4 and Calculator

Code

    /// Name: Ali Kurland
    /// Period: 6
    /// Program Name: Calculator
    /// File Name: Calculator.java
    /// Date Finished: 4/29/2016
    
    import java.util.Scanner;
    
    public class Calculator
    {
    	public static void main( String[] args )
    	{
    		Scanner keyboard = new Scanner(System.in);
    
    		String a, b, c;
            double d=0;
    		String op;
            double end=0;
            int q=0;
            
    		do
    		{
    			System.out.print("> ");
    			a  = keyboard.next();
    			b = keyboard.next();
    			c  = keyboard.next();
                
                double first = Double.valueOf(a);
                double second = Double.valueOf(c);
                
                if ( isNumeric(a) )
                {           
                    if ( b.equals("+") )
                        d = first + second;
                    else if ( b.equals("-") )
                        d = first - second;
                    else if ( b.equals("*") )
                        d = first * second;
                    else if ( b.equals("/") )
                        d = first / second;
                    else if ( b.equals("%") )
                        d = first % second;
                    else if ( b.equals("^") )
                    {   
                        d = first;
                        for ( int f=2; f<(second+1); f++ )
                        {
                            d = (first * d); 
                        }
                    }
                    else
                    {
                        System.out.println("Undefined operator: '" + b + "'.");
                        q = 1;
                    }
    
                    if ( (first != 0) && (q==0))    
                        System.out.println(d);
                    else if ( (first != 0) && (q!=0)) 
                        System.out.println();
                    else 
                        end = 1;
                }
                
    		} while ( end != 1 );
            
            System.out.println("Bye, now.");
    	}
    
    	public static boolean isNumeric( String s )
    	{
    		return ( isDouble(s) || isInteger(s) );
    	}
    
    	public static boolean isDouble( String s )
    	{
    		double n = 0;
    		try
    		{
    			n = Double.valueOf( s );
    		}
    
    		catch ( NumberFormatException e )
    		{
    			return false;
    		}
    
    		return true;
    	}
    
    	public static boolean isInteger( String a )
    	{
    		int n = 0;
    		try
    		{
    			n = Integer.valueOf( a );
    		}
    
    		catch ( NumberFormatException e )
    		{
    			return false;
    		}
    
    		return true;
    	}
    
    }
    

Picture of the output