實作按下 0 以外的數字要怎麼處理

AndroidCalculator/Calculator.swift

@@ -37,8 +37,18 @@ class Calculator {
         formula.append(formula.popLast()! + text)
       }
       
+    case "1", "2", "3", "4", "5", "6", "7", "8", "9":
+      if formula.last == "0" {
+        formula.removeLast()
+        formula.append(text)
+      } else if ["+", "-", "×", "÷"].firstIndex(of: formula.last!) != nil {
+        formula.append(text)
+      } else {
+        formula.append(formula.popLast()! + text)
+      }
+      
     default:
-      formula.append(text)
+      print(formula)
     }
   }
 }