diff --git a/bin/StringCalculator.class b/bin/StringCalculator.class
index a937b0c..c921184 100644
Binary files a/bin/StringCalculator.class and b/bin/StringCalculator.class differ
diff --git a/bin/StringCalculatorTest.class b/bin/StringCalculatorTest.class
index d44b83f..1f94b50 100644
Binary files a/bin/StringCalculatorTest.class and b/bin/StringCalculatorTest.class differ
diff --git a/src/StringCalculator.java b/src/StringCalculator.java
index 487916b..2e77640 100644
--- a/src/StringCalculator.java
+++ b/src/StringCalculator.java
@@ -1,9 +1,75 @@
 
 public class StringCalculator {
-	public int add(String numbersStr) {
+	public int add(String numbersStr) throws StringCalculatorException {
 		// Returns the sum of the numbers given in numbersStr
-		
+		int sum = 0;
+		if (numbersStr.isEmpty()) {
+			return 0;
+		} else {
+			int numericArray[] = getIntArray(numbersStr);
+			for (int i = 0; i < numericArray.length; i++) {
+				sum = sum + numericArray[i];
+			}
+			return sum;
+		}
 		// not yet implemented
-		return 0;
+
+	}
+
+	public int getLength(String str) {
+		return str.length();
+
+	}
+
+	public boolean handleLength(String str) {
+		if (str.length() < 20) {
+			return true;
+		} else {
+			return false;
+		}
+
+	}
+
+	public int[] getIntArray(String str) {
+		int arr[] = new int[str.length()];
+		int index = 0;
+		// System.out.println(str.length() + " ");
+		// if (isValid(str)) {
+		for (int i = 0; i < str.length(); i++) {
+			// if ((str.charAt(i)+str.charAt(i+1)+"") != "\n" ||
+			// (str.charAt(i)
+			// + "") != ",") {
+			if (!(str.charAt(i) + "").equals(",")) {
+				if (!(str.charAt(i) + "").equals("\n")) {
+					// System.out.println(str.charAt(i) + "");
+					arr[index++] = Integer.parseInt(str.charAt(i) + "");
+
+				}
+				// System.out.println(str.length() + " " + str.charAt(i) +
+				// "");
+			}
+		}
+		// }
+		return arr;
+
+	}
+
+	public boolean isValid(String str) {
+
+		return str.matches("(.*),\n(.*)") || str.matches("(.*)-(.*)") || str.matches("(.*)[a-z](.*)");
+		// return str.matches(",\n") || str.matches("-");
+		// boolean isvalid = true;
+		// System.out.println(str.length() + "");
+		/*
+		 * if (str.length() >= 2) { for (int i = 0; i < str.length() - 1; i++) {
+		 * if (((char)str.charAt(i) + (char)str.charAt(i + 1) +
+		 * "").equals(",\n")) { //System.out.println(str.charAt(i) +
+		 * str.charAt(i + 1) + ""); isvalid = false; break; }
+		 * 
+		 * } }
+		 */
+
+		// return isvalid;
+
 	}
 }
diff --git a/tests/StringCalculatorTest.java b/tests/StringCalculatorTest.java
index 4ec9afe..48c29de 100644
--- a/tests/StringCalculatorTest.java
+++ b/tests/StringCalculatorTest.java
@@ -9,4 +9,70 @@ public void test() {
 		fail("Not yet implemented");
 	}
 
+	@Test
+	public void simpleAddition() throws StringCalculatorException {
+
+		StringCalculator st1 = new StringCalculator();
+		assertEquals("output is correct", 12, st1.add("1236"));
+	}
+
+	@Test
+	public void additionWithComma() throws StringCalculatorException {
+
+		StringCalculator st1 = new StringCalculator();
+		assertEquals("output is correct", 12, st1.add("1,2,36"));
+	}
+
+	@Test
+	public void additionWithNewLine() throws StringCalculatorException {
+
+		StringCalculator st1 = new StringCalculator();
+		assertEquals("output is correct", 12, st1.add("1,2\n36"));
+	}
+
+	@Test
+	public void checkInValidAgainstnewlineWithcomma() throws StringCalculatorException {
+
+		StringCalculator st1 = new StringCalculator();
+		boolean res = st1.isValid("45,\n67");
+		assertTrue("String is Invalid", res);
+	}
+
+	@Test
+	public void checkInValidAgainstNegativeNumber() throws StringCalculatorException {
+
+		StringCalculator st1 = new StringCalculator();
+		boolean res = st1.isValid("45-67");
+		assertTrue("String is Invalid", res);
+	}
+	
+	@Test
+	public void checkInValidAgainstAnyInvalidInput() throws StringCalculatorException {
+
+		StringCalculator st1 = new StringCalculator();
+		boolean res = st1.isValid("457bcb");
+		assertTrue("String is Invalid", res);
+	}
+
+	@Test
+	public void isLenghtCorrect() throws StringCalculatorException {
+
+		StringCalculator st1 = new StringCalculator();
+		assertEquals("Length is correct", 5, st1.getLength("56556"));
+	}
+	@Test
+	public void testLenghtLimit() throws StringCalculatorException {
+
+		StringCalculator st1 = new StringCalculator();
+		boolean range=st1.handleLength("0463563465456760000");
+		assertTrue("Length is within range", range);
+	}
+
+	@Test
+	public void testEmptyResult() throws StringCalculatorException {
+
+		StringCalculator st1 = new StringCalculator();
+		assertEquals("Empty output", 0, st1.add(""));
+	}
+
 }