重構去除負號

AndroidCalculator/Calculator.swift

@@ -106,7 +106,9 @@ class Calculator {
         formula.append("0")
       }
       if formula.last!.firstIndex(of: "-") != nil {
-        formula.append(String(formula.popLast()!.split(separator: "-")[0]))
+        var number = formula.popLast()!
+        number.removeFirst()
+        formula.append(number)
       } else {
         formula.append("-" + formula.popLast()!)
       }