在輸入錯誤字符時嵌套另一個Java If/Else語句以打印輸出

Question

所以，根據輸入的響應，我的程序打印輸出You must enter either C or F or Y or N時出現問題。我曾嘗試在程序中放置其他if-else語句，但它無法正確運行並打破for循環。

public static void main(String[] args) { 

    for (int i = 0; i < 4; i++) { 
     System.out.println("Programmed by ."); 
     double standardCompact = 30.50; 
     double couponCompact = ((30.50)-(30.50 * 0.07)); 
     double standardFullSize = 40.50; 
     double couponFullSize = ((40.50)-(40.50 * 0.07)); 

     // Scanner Input 
     Scanner input = new Scanner(System.in); 
     System.out.print("Rent a Car? [Y or N]: "); 

     // Response String 
     String response = input.next().toUpperCase(); 

     if (response.equals("N")) { 
      System.out.println("You entered no. Bye."); 
     } 
     else if (response.equals("Y")) { 
      System.out.print("Compact or Full-Size? [C or F]: "); 
      response = input.next().toUpperCase(); 
      if (response.equals("C")) { 
       System.out.println("You selected Compact."); 

       //case1 
       System.out.print("Have coupon? [Y or N]: "); 
       response = input.next().toUpperCase(); 
       if (response.equals("N")) { 
        System.out.println("Price is " + standardCompact + " per day."); 
       } 
       else if (response.equals("Y")) { 
        System.out.println("Price is " + couponCompact + " per day."); 
       } 
      } 
      else if (response.equals("F")) { 
       System.out.println("You have selected Full-Size. "); 

       //case 2 
       System.out.print("Have coupon? [Y or N]: "); 
       response = input.next().toUpperCase(); 
       if (response.equals("N")) { 
        System.out.println("Price is " + standardFullSize + " per day."); 
       } 
       else if (response.equals("Y")) { 
        System.out.println("Price is " + couponFullSize + " per day."); 
       } 
      } 
     } 
    } 
} 

Answer 1

當構建一個if語句，else可以用來處理沒有被前面if或else if陳述抓住所有其他條件。

int x = 0; 

if(x ==1){ 
    System.out.println("1"); 
}else if(x ==2){ 
    System.out.println("2"); 
}else{ 
    //execute if none of the other conditionals are true 
    System.out.println("Other Conditions not met"); 
} 

//Outputs: Other Conditions not met 

Answer 2

考慮使用布爾標誌和'else'語句的組合。因此，如果用戶未輸入N或Y，則將此標誌設置爲true。同樣，如果用戶沒有輸入C或F，則將此標誌設置爲true。

稍後，在for循環結束時，檢查此標誌。如果確實如此，請打印您的消息。這可能值得一試...

public static void main(String[] args) { 

    boolean notValidCharacter; 

    for(int i = 0; i < 4; i++) { 

     notValidCharacter = false; 

     System.out.println("Programmed by ."); 

     double standardCompact = 30.50; 
     double couponCompact = ((30.50)-(30.50 * 0.07)); 
     double standardFullSize = 40.50; 
     double couponFullSize = ((40.50)-(40.50 * 0.07)); 

     //Scanner Input 
     Scanner input = new Scanner(System.in); 
     System.out.print("Rent a Car? [Y or N]: "); 

     //Response String 
     String response = input.next().toUpperCase(); 

     if (response.equals("N")){ 
      System.out.println("You entered no. Bye. "); 
     } 
     else if (response.equals("Y")) { 
      System.out.print("Compact or Full-Size? [C or F]: "); 

      response = input.next().toUpperCase(); 
      if (response.equals("C")) { 
       System.out.println("You selected Compact. "); 

       //case1 
       System.out.print("Have coupon? [Y or N]: "); 
       response = input.next().toUpperCase(); 
       if (response.equals("N")) { 
        System.out.println("Price is" + " " + standardCompact + " " + "per  day."); 
       } 
       else if (response.equals("Y")) { 
        System.out.println("Price is" + " " + couponCompact + " " + "per day."); 
       } 
      } 
      else if(response.equals("F")) { 
       System.out.println("You have selected Full-Size. "); 

       //case 2 

       System.out.print("Have coupon? [Y or N]: "); 
       response = input.next().toUpperCase(); 
       if (response.equals("N")) { 
        System.out.println("Price is" + " " + standardFullSize + " " + "per day."); 
       } 
       else if (response.equals("Y")) { 
        System.out.println("Price is" + " " + couponFullSize + " " + "per day."); 
       } 
      } 
      else { 
       notValidCharacter = true; 
      } 
     } 
     else { 
      notValidCharacter = true; 
     } 

     if (notValidCharacter) { 
      System.out.println("You must enter either C or F or Y or N"); 
     } 
    } 
}