Basic functions work

Added buttons work somewhat
-- 9 -> sqr -> anyNumber -> =

src/main/java/rocks/zipcode/calcskin/CalcEngine.java

     }
 
     public double add(double v, double v1) {
-        return Double.NaN;
+        return v + v1;
     }
 
     public double subtract(double v, double v1) {
-        return Double.NaN;
+        return v - v1;
     }
 
     public double multiply(double v, double v1) {
-        return Double.NaN;
+        return v * v1;
     }
 
     public double divide(double v, double v1) {
-        return Double.NaN;
+        return v / v1;
+    }
+
+    public double square(double curNum) {
+        return Math.pow(curNum, 2.0D);
+    }
+
+    public double squareRoot(double curNum) {
+        return Math.sqrt(curNum);
+    }
+
+    public double exponent(double curNum, double userExponent) {
+        return Math.pow(curNum, userExponent);
+    }
+
+    public double invert(double curNum) {
+        return 1.0D / curNum;
     }
 }

src/main/java/rocks/zipcode/calcskin/CalcSkin.java

         launch(args);
     }
     private static final String[][] template = {
-            { "7", "8", "9", "/" },
-            { "4", "5", "6", "*" },
-            { "1", "2", "3", "-" },
-            { "0", "c", "=", "+" }
+            { "7", "8", "9", "/", "sqr" },
+            { "4", "5", "6", "*", "sqRt" },
+            { "1", "2", "3", "-", "exp" },
+            { "0", "c", "=", "+", "inv" }
     };
 
     private final Map<String, Button> accelerators = new HashMap<>();
     private DoubleProperty currentValue = new SimpleDoubleProperty();
     private CalcEngine calcEngine = new CalcEngine();
 
-    private enum Op { NOOP, ADD, SUBTRACT, MULTIPLY, DIVIDE }
+    private enum Op { NOOP, ADD, SUBTRACT, MULTIPLY, DIVIDE, SQUARE, SQROOT, EXPON, INVERS }
 
     private Op curOp   = Op.NOOP;
     private Op stackOp = Op.NOOP;
                 makeClearButton(button);
             } else if ("=".equals(s)) {
                 makeEqualsButton(button);
+            } else if ("sqr".equals(s)){
+                makeEqualsButton(button);
             }
         }
 
     private ObjectProperty<Op> determineOperand(String s) {
         final ObjectProperty<Op> triggerOp = new SimpleObjectProperty<>(Op.NOOP);
         switch (s) {
-            case "+": triggerOp.set(Op.ADD);      break;
-            case "-": triggerOp.set(Op.SUBTRACT); break;
-            case "*": triggerOp.set(Op.MULTIPLY); break;
-            case "/": triggerOp.set(Op.DIVIDE);   break;
+            case "+":    triggerOp.set(Op.ADD);      break;
+            case "-":    triggerOp.set(Op.SUBTRACT); break;
+            case "*":    triggerOp.set(Op.MULTIPLY); break;
+            case "/":    triggerOp.set(Op.DIVIDE);   break;
+            case "sqr":  triggerOp.set(Op.SQUARE);   break;
+            case "sqRt": triggerOp.set(Op.SQROOT);   break;
+            case "exp" : triggerOp.set(Op.EXPON);    break;
+            case "inv" : triggerOp.set(Op.INVERS);   break;
         }
         return triggerOp;
     }
             }
         });
     }
-
+/*
+    private void makeSquareButton(Button button) {
+        button.setStyle("-fx-base: mistyrose;");
+        button.setOnAction(new EventHandler<ActionEvent>() {
+            @Override
+            public void handle(ActionEvent actionEvent) {
+                currentValue.set(calcEngine.square(currentValue.get()));
+            }
+        });
+    }
+*/
     private void makeEqualsButton(Button button) {
         button.setStyle("-fx-base: ghostwhite;");
         button.setOnAction(new EventHandler<ActionEvent>() {
                     case SUBTRACT: currentValue.set(calcEngine.subtract(previousValue.get(), currentValue.get())); break;
                     case MULTIPLY: currentValue.set(calcEngine.multiply(previousValue.get(), currentValue.get())); break;
                     case DIVIDE:   currentValue.set(calcEngine.divide(previousValue.get(), currentValue.get())); break;
+                    case SQUARE:   currentValue.set(calcEngine.square(previousValue.get())); break;
+                    case SQROOT:   currentValue.set(calcEngine.squareRoot(previousValue.get())); break;
+                    case EXPON:    currentValue.set(calcEngine.exponent(previousValue.get(), currentValue.get())); break;
+                    case INVERS:   currentValue.set(calcEngine.invert(previousValue.get())); break;
                 }
             }
         });
     }
+
+
 }