diff --git a/bin/StringCalculator.class b/bin/StringCalculator.class
index a937b0c..7dc706f 100644
Binary files a/bin/StringCalculator.class and b/bin/StringCalculator.class differ
diff --git a/bin/StringCalculatorException.class b/bin/StringCalculatorException.class
index 4bd9894..83a4b8e 100644
Binary files a/bin/StringCalculatorException.class and b/bin/StringCalculatorException.class differ
diff --git a/bin/StringCalculatorTest.class b/bin/StringCalculatorTest.class
index d44b83f..2df168e 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..b69f21a 100644
--- a/src/StringCalculator.java
+++ b/src/StringCalculator.java
@@ -1,9 +1,112 @@
+//import java.text.ParseException;
 
 public class StringCalculator {
-	public int add(String numbersStr) {
+	
+		
+			
+	public int add(String numbersStr) throws StringCalculatorException {
+		
 		// Returns the sum of the numbers given in numbersStr
 		
-		// not yet implemented
-		return 0;
+		numbersStr=checkIfEmpty(numbersStr);		
+		numbersStr=LinesToCommas(numbersStr); //replaces "\n" with ","
+		checkInvalidCommas(numbersStr); //Checks if there is more than 1 comma in a row
+		
+		String [] StrArray=removeCommas(numbersStr); //removes commas from the string
+		
+		checkForNumeric(StrArray);//checks if is numeric, if not, throws exception
+		int[] intArray=ChangeToInt(StrArray);//Strings to integer
+		checkForNegatives(intArray);//Checks that numbers are positive, if not, throws exception
+		checkNumberCount(intArray);//Checks how many numbers given, if more than 2, throws exception
+						
+		int sum=0;
+		for (int i : intArray) {
+			sum=sum+i;
+	    }
+		System.out.print("Sum is: ");
+        System.out.print(sum);
+		
+		return sum;
+	}
+	
+	public String checkIfEmpty(String numbersStr) {
+		if (numbersStr=="") {
+			numbersStr="0";
+		}
+		return numbersStr;
+	}
+
+	public void checkNumberCount(int[] intArray) throws StringCalculatorException {
+		
+		if (intArray.length>2) {
+			throw new StringCalculatorException("");
+			
+		}
+		
 	}
+
+	public int[] ChangeToInt(String[] strArray) {
+		String[] arrOfStr =strArray; 
+				
+		int[] arrOfInt = new int[arrOfStr.length]; 
+        
+		for (int i = 0; i < arrOfStr.length; i++) {
+	       
+			arrOfInt[i] = Integer.parseInt(arrOfStr[i]);
+		}
+	        
+		return arrOfInt;
+	}
+
+	public void checkForNegatives(int[] intArray) throws StringCalculatorException {
+		int[] array = intArray;
+		for (int i=0; i<array.length;i++)
+		{
+			if (array[i]<0) {
+				throw new StringCalculatorException("");
+				}
+		}
+		
+	}
+
+	public void checkForNumeric(String[] strArray) throws StringCalculatorException {
+		
+		String[] arrOfStr =strArray; 
+					
+		
+		int[] arrOfInt = new int[arrOfStr.length];  
+        
+		for (int i = 0; i < arrOfStr.length; i++) {
+	        try {
+			arrOfInt[i] = Integer.parseInt(arrOfStr[i]);
+	        }
+	        catch (NumberFormatException e) {
+	            throw new StringCalculatorException("");      
+	        	}		
+			}       		
+		}
+		
+	
+
+	public String LinesToCommas(String numbersStr) {
+		String NoLines=numbersStr.replace("\n",",");
+		return NoLines;
+		
+	}
+
+	public String[] removeCommas(String numbersStr) {
+		String [] NoCommas=numbersStr.split(",",-1);
+		return NoCommas;
+	}
+
+	public void checkInvalidCommas(String numbersStr) throws StringCalculatorException { 
+		int a=numbersStr.indexOf(",,");
+				
+		if (a>=0) {
+		throw new StringCalculatorException("");
+		}
+	}
+
+	
+	
 }
diff --git a/src/StringCalculatorException.java b/src/StringCalculatorException.java
index da71147..7d840a9 100644
--- a/src/StringCalculatorException.java
+++ b/src/StringCalculatorException.java
@@ -1,4 +1,8 @@
 
 public class StringCalculatorException extends Exception {
 
+	public StringCalculatorException(String string) {
+		System.out.println(string);
+	}
+
 }
diff --git a/tests/StringCalculatorTest.java b/tests/StringCalculatorTest.java
index 4ec9afe..0899865 100644
--- a/tests/StringCalculatorTest.java
+++ b/tests/StringCalculatorTest.java
@@ -1,12 +1,87 @@
 import static org.junit.Assert.*;
 
+import java.util.Arrays;
+
 import org.junit.Test;
 
+import junit.framework.Assert;
+
 public class StringCalculatorTest {
 
+	
+	
 	@Test
-	public void test() {
-		fail("Not yet implemented");
+	public void TestStringCalculator_ChangeLinesToCommas() throws StringCalculatorException{
+		//Arrange
+		StringCalculator calculator = new StringCalculator();
+		//act		
+		assertEquals("Fail","1,2,66",calculator.LinesToCommas("1\n2,66"));//		
+	}
+	
+	@Test(expected = StringCalculatorException.class)
+	public void TestStringCalculator_CommasInaRowShouldThrowException() throws StringCalculatorException {
+		StringCalculator calculator = new StringCalculator();
+		calculator.checkInvalidCommas("1,,2,3");	
 	}
+	
+	@Test
+	public void TestStringCalculator_RemoveCommas() throws StringCalculatorException {
+		//Arrange
+		StringCalculator calculator = new StringCalculator();
+		
+		String input=("1,2,3");
+		String[] expected= {"1","2","3"};
+		assertArrayEquals(expected,calculator.removeCommas(input));
+		}
+				
+	
+	@Test(expected=StringCalculatorException.class)
+	public void TestStringCalculator_NotNumericThrowException() throws StringCalculatorException{
+		//Arrange
+		StringCalculator calculator = new StringCalculator();
+		//act
+		String[] input= {"a","2"};
+		calculator.checkForNumeric(input);
+		}
+	
+	@Test
+	public void TestStringCalculator_ChangeToIntegerArray() throws StringCalculatorException {
+		//Arrange
+		StringCalculator calculator = new StringCalculator();
+		
+		String[] input= {"1","2","3"};
+		int[] expected= {1,2,3};
+		
+		assertArrayEquals(expected,calculator.ChangeToInt(input));
+		}
+		
+	@Test(expected = StringCalculatorException.class)
+	public void TestStringCalculator_NegativeThrowsException() throws StringCalculatorException {
+		StringCalculator calculator = new StringCalculator();
+		int[] input= {-2,3,5};
+		calculator.checkForNegatives(input);
+		}
 
+	
+	@Test (expected=StringCalculatorException.class)
+	public void TestStringCalculator_TooManyNumbersThrowException() throws StringCalculatorException {
+			StringCalculator calculator = new StringCalculator();
+			int[] input= {1,55,5};
+			calculator.checkNumberCount(input);
+			}
+			
+	
+	@Test
+	public void TestStringCalculator_NoNumbersReturnsZero() throws StringCalculatorException {
+		StringCalculator calculator = new StringCalculator();
+		//act
+		assertEquals("Fail", 0, calculator.add(""));		
+	}
+	@Test
+	public void TestStringCalculator_AddsGivenNumbers() throws StringCalculatorException {
+		StringCalculator calculator = new StringCalculator();
+		//act
+		assertEquals("Fail", 20, calculator.add("14,6"));		
+	}
 }
+