CSC436: Homework: To hand in [14/22]

Here is a controller for a simple calculator, written in Java.

Copy and paste this onto your home machine and run it.

To watch it work, you should run it and type in one character per line on the console, like this (output in red):

1
val:1 old:0 op:= isClean:false
1
val:11 old:0 op:= isClean:false
*
val:11 old:11 op:* isClean:true
2
val:2 old:11 op:* isClean:false
=
val:22 old:2 op:= isClean:true
+
val:22 old:2 op:+ isClean:true
3
val:3 old:22 op:+ isClean:false
3
val:33 old:22 op:+ isClean:false
=
val:55 old:33 op:= isClean:true

The val is what is displayed on the face of the calculator.

Your homework is to write version of this in raw javascript, with html and css by adapting this code to javascript and providing a view.

Here is an example, which was generated by translation from source written in agda [Search].

Your app should allow input by tapping the buttons, or by pressing the keys on a keyboard.

This code works without parentheses. If you are interested in how to add them, see here [Search].

import java.util.Scanner;
public class ZSimpleCalculator {
  int val = 0;            // the current value
  int old = 0;            // the old value 
  char op = '=';          // the previous operation
  boolean isClean = true; // is the new value clean?
  
  public String toString () {
    return String.format ("val:%d old:%d op:%c isClean:%b", this.val, this.old, this.op, this.isClean);
  }
  public void process (char c) {
    if (isClear (c)) {

      this.val = 0;
      this.old = 0;
      this.op = '=';
      this.isClean = true;
      
    } else if (isDigit (c)) {
      
      int d = evalDigit (c);
      if (this.isClean) {
        // start a new value
        this.old = this.val;  
        this.val = d;
      } else {
        // add to the existing value
        this.val = (this.val * 10) + d;
      }
      this.isClean = false;
      
    } else if (isOp (c)) {
      
      int v = evalOp (this.op, this.old, this.val);
      if (! this.isClean) {
        // start a new value
        this.old = this.val;  
      }
      this.val = v;
      this.op = c;
      this.isClean = true;
      
    }
  }

  public static boolean isOp (char c) {
    switch (c) {
    case '=' : return true;
    case '+' : return true;
    case '-' : return true;
    case '*' : return true;
    }
    return false;
  }
  public static int evalOp (char c, int m, int n) {
    switch (c) {
    case '=' : return n; // m is the old value, n is the new value
    case '+' : return m + n;
    case '-' : return m - n;
    case '*' : return m * n;
    }
    throw new Error ();
  }
  public static boolean isDigit (char c) {    
    return c >= '0'  && c <= '9';
  }
  public static int evalDigit (char c) {    
    return c - '0';
  }
  public static boolean isClear (char c) {    
    return c == 'c';
  }
  public static void main (String[] args) {
    ZSimpleCalculator eval = new ZSimpleCalculator ();
    Scanner in = new Scanner (System.in);
    while (in.hasNext ()) {
      String s = in.nextLine ();
      for (int i = 0; i < s.length(); i++){
          char c = s.charAt(i);  
          eval.process (c);
          System.err.println (eval.toString ());
      }
    }
    in.close ();
  }
}