Assignment 3: A Simple Calculator in Angular2

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 third homework is to write version in Angular2 that works like this by adapting this code to javascript and providing a view.

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

If you are interested in adding parentheses, see here

```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 ();
}
}```