         case Equals
     }
     
+    private let binaryOps = ["+", "-", "×", "÷"]
+    
     func performOperation(symbol: String) {
         internalProgram.append(symbol as AnyObject)
         

    func setOperand(operand: Double) {
        accumulator = operand
//        description += String(operand)
        descriptionCollection.append(String(operand))
        
        internalProgram.append(operand as AnyObject)
    }

            }
        } else if symbol == "=" && (descriptionCollection.filter{$0 == "="}).count >= 1 {
            descriptionCollection = descriptionCollection.filter{$0 != "="}
            descriptionCollection.append(symbol)
        } else if symbol == "=" && binaryOps.contains(descriptionCollection.last!) {
            descriptionCollection.append(String(accumulator))
            descriptionCollection.append(symbol)
        } else {
            descriptionCollection.append(symbol)
