//import API's needed here:
import java.util.Scanner;

public class CalculatorDriver23 
{  

        public static void main(String args[ ]) 
        {
             Calculator one = new Calculator();  
             Calculator two = new Calculator('+');   
				 one.calculate();
				  
         } //closing main method
         
         
         
         
         
         
         
         
         
         public static class Calculator
         {
         private double a; //operand a
         private double b; //operand b
         private double ans; //result of calculation
         private char op; //operator
         private double mem; //result of previous calculation
         private boolean newData;//used if = was found to start new problem otherwise use memory for first operand
         
         
         Calculator() //default constructor with no parameters - sets attributes to 0
         {
            this.a=0;
            this.b=0;
            this.ans=0;
            this.op = ' ';
            this.mem =0;
            this.newData=true;
         }
         
         
         Calculator(char x)//constructor that sets operator only
         {
            this.a=0;
            this.b=0;
            this.ans=0;
            this.op = x;
            this.mem =0;
            this.newData=true;

         }
         void calculate()
         { 
            Scanner kbd = new Scanner(System.in); //to accept keyboard input
            int i; //index variable to access string array
            boolean on = true; //run calculator until user enters lowercase o to turn off calculator
            String []inp = new String[4]; //4 rows of data: operand a, operator, operand b, = 
            inp[0]="x";
            inp[2]="x"; //used to run for loop - that user did not yet enter o to turn off
            do{
            if(newData==true)//full new equation a,operator, b, =
            {
            for(i=0;i<inp.length && inp[0].charAt(0) != 'o';i++) //get data in string array as listed above
               inp[i] = kbd.nextLine();   //if o is entered for loop stops before filling entire array
            }
            else //using memory
            {
               setOp(inp[3].charAt(0));//from previous loop last operator was not =

               for(i=2;i<inp.length && inp[2].charAt(0) != 'o';i++) //get data in string array as listed above
               inp[i] = kbd.nextLine();   //if o is entered for loop stops before filling entire array
               
            
            }
            if(inp[0].charAt(0) == 'o'||inp[2].charAt(0) == 'o') //if o is found, turn off calculator
               on = false;
            else //calculate
            {
            
            if(newData==true && (inp[0].charAt(0) >= '0' && inp[0].charAt(0) <= '9'||inp[0].charAt(0)=='.')) //data was taken in as String 
              this.a = Double.parseDouble(inp[0]); //covert it to the double data type to be able to do math manipulation
            
            if (newData==true)
               setOp(inp[1].charAt(0));//set the operator for the new data
                                        
            if(inp[2].charAt(0) >= '0' && inp[2].charAt(0) <= '9'|| inp[2].charAt(0) == '.') //same for the 2nd operand - pay close attention to the index
               this.b = Double.parseDouble(inp[2]);
               
            if(inp[3].charAt(0) == '=') //if = is found do the math
            {
               
            if(this.op == '+')
               {
               add(a,b,inp[3].charAt(0));
               this.newData=true;
               }
               
            if(this.op == '-')
               {
               subtract(a,b,inp[3].charAt(0));
               this.newData=true;
               }

   
           
            }//end of if found =
            
            
            else if (inp[3].charAt(0) == '+')
            {
               
            if(this.op == '+')
               {
                  add(a,b,inp[3].charAt(0));
                  setA();
                  this.newData =false;
               }
            if(this.op == '-')
               {
               subtract(a,b,inp[3].charAt(0));
               setA();
               this.newData = false;
               }

           
            }//end of if found +
            
            
            else if (inp[3].charAt(0) == '-')//subtract
            {
               
            if(this.op == '+')
               {
                  add(a,b,inp[3].charAt(0));
                  setA();
                  this.newData =false;
               }
            if(this.op == '-')
               {
               subtract(a,b,inp[3].charAt(0));
               setA();
               this.newData = false;
               }

           
            }//end of if found -

            
            }//end of else it was not 'o'
            
            }while(on);
         }//end of calculate
         
         void add(double a, double b, char end)
         {
            this.ans = a+b;
            if(end == '=')//display result
            System.out.println(this.ans);
            this.mem = this.ans;
            //return this.ans;
         }
         
         
         void subtract(double a, double b, char end)
         {
            this.ans = a-b;
            
            if(end == '=')//display result
               System.out.println(this.ans);
            this.mem = this.ans;
            //return this.ans;
         }
         
         void setA()
         {
         this.a = this.mem;
         }
         
         void setOp(char z)
         {
         this.op = z;
         }
         
         }//end of Calculator object
} //closing class header