else if (src == referenca.buttonPlus)//when someone press button +
			{
				
num=referenca.getDisplay();//gets the number that someone typed and saves it into variable num

numStringToDouble = Double.parseDouble(num);//Converts String to Double 

matOperacija="+"; //saves mathematical operations - I have set this variable to be INT but I am not sure what should it be INT,CHAR,STRING...
							
referenca.setDisplay ("",""); //sets blank display 
				
			}
			
//the same as buttonPlus
			else if (src == referenca.buttonMinus)
			{
				num = referenca.getDisplay();
				numStringToDouble = Double.parseDouble(num);
				matOperacija="-";
				
				referenca.setDisplay("","");
			}
			
			else if (src == referenca.buttonEqual)
			{
String equal= referenca.getDisplay();//gets displayed number

Double newEqual =Double.parseDouble(equal);//converts displayed number into double

Double result = //here is where I should use a mathematical operation but I do not know how.

String newResult = Double.toString(result); // converts Double into String
				
referenca.setDisplay(newResult);//sets display to a new result
				
			}