循环用户输入，直到满足条件

Question

我需要让用户输入一个数字来用作范围的开始，然后输入另一个数字作为范围的结束。 起始编号必须为0或更大，终止编号不能大于1000。两个数字都必须被10整除。我找到了满足这些条件的方法，但是如果不满足这些条件，我的程序只会告诉用户他们的输入不正确。 我是否可以对其进行编码，以便在用户输入后检查是否满足条件，如果条件没有环回，请再次输入。 这是我到目前为止的代码。

    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

轻松做：

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

您需要使用一段时间，例如：

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

应该这样做。

Answer 3

通用过程是：

1. 无限循环读取输入。
2. break; 满足条件时退出循环的语句。

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.");
}

如果在无效输入后您只想显示错误消息而不重复初始提示消息，请将初始提示消息移到循环的上方/外部。

如果您不需要单独的错误消息，则可以重新安排代码以使用do-while循环检查条件，该条件稍短一些：

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));