循環用戶輸入，直到條件滿足

Question

我需要讓用戶輸入一個數字作爲範圍的開始，然後輸入另一個數字，即範圍的結尾。起始數字必須爲0或更大，結束數字不能大於1000.兩個數字都必須可以被10整除。我找到了一種方法來滿足這些條件，但是如果它們不符合我的程序只是告訴用戶他們的輸入不正確。是否可以對其進行編碼，以便在用戶輸入之後將檢查以確保滿足條件，並且如果它們沒有回送並再次輸入它們。這是我迄今爲止的代碼。

Scanner keyboard = new Scanner(System.in); 
    int startr; 
    int endr; 
    System.out.println("Enter the Starting Number of the Range: "); 
    startr=keyboard.nextInt(); 
    if(startr%10==0&&startr>=0){ 
     System.out.println("Enter the Ending Number of the Range: "); 
     endr=keyboard.nextInt(); 
     if(endr%10==0&&endr<=1000){ 

     }else{ 
      System.out.println("Numbers is not divisible by 10"); 
     } 
    }else{ 
     System.out.println("Numbers is not divisible by 10"); 
    } 

Answer 1

易與DO-同時：

Scanner keyboard = new Scanner(System.in); 
int startr, endr; 
boolean good = false; 
do 
{ 
    System.out.println("Enter the Starting Number of the Range: "); 
    startr = keyboard.nextInt(); 
    if(startr % 10 == 0 && startr >= 0) 
    good = true; 
    else 
    System.out.println("Numbers is not divisible by 10"); 
} 
while (!good); 

good = false; 
do 
{ 
    System.out.println("Enter the Ending Number of the Range: "); 
    endr = keyboard.nextInt(); 
    if(endr % 10 == 0 && endr <= 1000) 
     good = true; 
    else 
     System.out.println("Numbers is not divisible by 10"); 
} 
while (!good); 

// do stuff 

Answer 2

您需要使用時，是這樣的：

while conditionsMet is false 
    // gather input and verify 
    if user input valid then 
     conditionsMet = true; 
end loop 

應該這樣做。

Answer 3

全目的的程序是：

1. 讀輸入中無限循環。
2. 當條件滿足時，使用break;語句退出循環。

實施例：

Scanner keyboard = new Scanner(System.in); 
int startr, endr; 

for (;;) { 
    System.out.println("Enter the starting number of the range: "); 
    startr = keyboard.nextInt(); 
    if (startr >= 0 && startr % 10 == 0) break; 
    System.out.println("Number must be >= 0 and divisible by 10."); 
} 

for (;;) { 
    System.out.println("Enter the ending number of the range: "); 
    endr = keyboard.nextInt(); 
    if (endr <= 1000 && endr % 10 == 0) break; 
    System.out.println("Number must be <= 1000 and divisible by 10."); 
} 

如果無效輸入之後要，而無需重複初始提示信息只顯示該錯誤消息，移動至初始提示消息的正上方/外循環。

如果沒有需要單獨的錯誤信息，則可以重新安排代碼以使用do-while循環檢查的條件，這僅僅是一個短一點：

Scanner keyboard = new Scanner(System.in); 
int startr, endr; 

do { 
    System.out.println("Enter the starting number of the range."); 
    System.out.println("Number must be >= 0 and divisible by 10: "); 
    startr = keyboard.nextInt(); 
} while (!(startr >= 0 && startr % 10 == 0)); 

do { 
    System.out.println("Enter the ending number of the range."); 
    System.out.println("Number must be <= 1000 and divisible by 10: "); 
    endr = keyboard.nextInt(); 
} while (!(endr <= 1000 && endr % 10 == 0));