Question

如何以及在何处为此程序添加循环，以便程序继续执行，然后在用户输入介于100和999之间的有效数字后结束？

import java.util.*;

public class numLoop{
public static void main(String[] arg){
  Scanner sc = new Scanner(System.in);
  int number = 0;

  try{
     Scanner reader = new Scanner(System.in);
     System.out.print("Enter a number between 100 and 999: ");
     number = reader.nextInt();

     if(number > 999 || number < 100)
        System.out.println("\nYour number was invalid.");

     else
        System.out.println("\nThe number " + number + " was vaild.");

      }
      catch(InputMismatchException ime){
            System.out.println("You didn't enter a number.");

     }
 }
}

Answer 1

将整个try / catch放在while循环中：

while (number < 100 || number > 999)
{
    // ...
}

或者使用while (true) { }或for (;;) { }将其置于无限循环中，然后在输入有效数字时添加条件break：

if (number < 100 || number > 999)
{
    // handle invalid entry
}

else
{
    // handle valid entry

    break; // exit loop
}

Answer 2

使用while循环可以实现以下逻辑

（伪代码）

Input a number
while (number is not valid)
    Tell them something went wrong
    Input another number
Valid number was entered, do something about it

while循环本身看起来像

while (condition) {
   // code to run while condition is true
}

Answer 3

import java.util.*;

public class numLoop{
public static void main(String[] arg){
  Scanner sc = new Scanner(System.in);
  int number = 0;

  try{
     Scanner reader = new Scanner(System.in);
     System.out.print("Enter a number between 100 and 999: ");
     number = reader.nextInt();

     while(number > 999 || number < 100){
        System.out.println("\nYour number was invalid.");
        number = reader.nextInt();
     }

     System.out.println("\nThe number " + number + " was vaild.");


      }catch(InputMismatchException ime){
            System.out.println("You didn't enter a number.");

     }
 }
}

Answer 4

你也可以像这样使用while（true）break循环：

    import java.util.*;

    public class numLoop{
    public static void main(String[] arg){
      Scanner sc = new Scanner(System.in);
      int number = 0;
    while(true){
      try{
         Scanner reader = new Scanner(System.in);
         System.out.print("Enter a number between 100 and 999: ");
         number = reader.nextInt();

         if(number > 999 || number < 100)
            System.out.println("\nYour number was invalid.");

         else
            System.out.println("\nThe number " + number + " was vaild.");
            break;
          }
          catch(InputMismatchException ime){
                System.out.println("You didn't enter a number.");

         }
     }
    }
  }

不是每个人都警告这是良好的代码练习。

Answer 5

在您现有的try添加

之前的三个小行...

while(true) // you could (and should) add braces (for the look of it).
            // could also have used for(;;)

在这里

else
  System.out.println("\nThe number " + number + " was vaild.");

然后你需要一个

else {
  System.out.println("\nThe number " + number + " was vaild.");
  break;  // End the infinite loop.
}

如何为此程序添加一个循环并让它继续运行直到程序为真？

5 个答案: