實作按下 . 要怎麼處理

AndroidCalculator/Calculator.swift

@@ -47,6 +47,15 @@ class Calculator {
         formula.append(formula.popLast()! + text)
       }
       
+    case ".":
+      if formula.last!.firstIndex(of: ".") != nil {
+        return
+      } else if ["+", "-", "×", "÷"].firstIndex(of: formula.last!) != nil {
+        return
+      } else {
+        formula.append(formula.popLast()! + text)
+      }
+      
     default:
       print(formula)
     }