diff --git a/calculator.js b/calculator.js
index caf34db..40d8407 100644
--- a/calculator.js
+++ b/calculator.js
@@ -1,5 +1,5 @@
 function isNumber(numStr){
-  var re = /^[0-9\.]+$/; 
+  var re = /^-?[0-9]+(.?[0-9]+)?$/; 
   return re.test(numStr);
 }
 
@@ -11,5 +11,16 @@ function substract(num1, num2){
   return num1 - num2;
 }
 
+function mul(num1, num2){
+	return num1 * num2;
+}
+
+function div(num1, num2){
+	return num1 / num2;
+}
+
 module.exports.add = add;
+module.exports.substract = substract;
+module.exports.mul = mul;
+module.exports.div = div;
 module.exports.isNumber = isNumber;
diff --git a/index.html b/index.html
index cc6a9d9..92c7fb4 100644
--- a/index.html
+++ b/index.html
@@ -22,6 +22,8 @@ <h1>Silly Calculator</h1>
     <select id="operator" size="1">
       <option value="add">+</option>
       <option value="substract">-</option>
+	  <option value="mul">×</option>
+	  <option value="div">÷</option>
     </select>
     <input type="text" id="num2" value="1" />
     <div>=</div>
diff --git a/main.js b/main.js
index 957a234..e185155 100644
--- a/main.js
+++ b/main.js
@@ -15,6 +15,12 @@ window.onload = function(){
     }
     else if (operator == "substract"){
       document.getElementById('ans').value = substract(num1, num2);
+    }
+	else if (operator == "mul"){
+      document.getElementById('ans').value = mul(num1, num2);
+    }
+	else if (operator == "div"){
+      document.getElementById('ans').value = div(num1, num2);
     }
     else {
       alert("Bad operator!")
diff --git a/package.json b/package.json
index d727f6d..5783ea8 100644
--- a/package.json
+++ b/package.json
@@ -8,7 +8,8 @@
   "author": "Askeing Yen & Shing Lyu",
   "license": "MPLv2",
   "dependencies": {
-    "mocha": "~2.3.2"
+    "mocha": "~2.3.2",
+	"sinon": "1.17.2"
   },
   "repository":{}
 }
diff --git a/test/test_calculator.js b/test/test_calculator.js
index 13f6205..302d86f 100644
--- a/test/test_calculator.js
+++ b/test/test_calculator.js
@@ -1,10 +1,36 @@
 var assert = require('assert');
 var cal = require('../calculator.js')
+var sinon = require('sinon');
 
 describe('Calculator', function(){
-  describe('add', function(){
     it('add', function(){
       assert.equal('2', cal.add(1, 1));
     })
-  })
+  
+	it('substract',function(){
+	   assert.equal('1' , cal.substract(2,1));
+	})
+  
+	it('mul',function(){
+	   assert.equal('6' , cal.mul(2,3));
+	})
+  
+	it('div',function(){
+	   assert.equal('0.5' , cal.div(1,2));
+	})
+})
+
+describe('Negative path', function(){
+	it('isNumber',function(){
+		assert.equal(false,cal.isNumber('13A'));
+	})
+})
+
+describe('Sinon', function(){
+	it('stub mul function',function(){
+		var stub = sinon.stub().returns(30);
+		var proxy = cal.mul(stub(), 5);
+		
+		assert.equal(150, proxy);
+	})
 })