如何使用“for”循环运行该程序

Question

我制作了一个程序，提示用户输入两个数字。如果这些数字是偶数倍，我将显示两个数字之间的所有奇数。如果这些数字不是偶数，我会要求用户重新输入这两个数字。我已经使用 while 循环成功地制作了这个程序。但我想知道如何使用“for”循环来制作这样的程序。这是我使用 while 循环的原始代码。所有提示和建议都会有所帮助。

/**
 * Description: This program takes two integers entered by the user and 
 * displays the odd numbers between the integers if the integers entered
 * are even multiples. If the integers entered are not even multiples,
 * the program will prompt the user to re enter the integers.
 */

/**
 * This is the main loops class. This class
 * includes the main method as well
 * as the program method.
 */

public class loops { 

/**
 * This is the main method. It provides an 
 * entry into the program.
 */
  public static void main (String []args) {

    loops lps = new loops();//Instantiating loops class.
    lps.program();//Invoking the program method on the loops class. 

  }


/**
 * This is the program method. This
 * method will carry out the program
 * functions.
 */
  public void program() {

/**
 * Declaring variables that
 * will be used in the program.
 */
    int firstNumber;
    int secondNumber;   
    int finalNumber;

    java.util.Scanner input=new java.util.Scanner(System.in);//Using the Java utility scanner.

    try {//Try statement. Used to handle exceptions.
    do {//Using a do-while loop.

/**
 * Prompting the user to enter two
 * integers. Then taking the remainder
 * of the integers.
 */
      System.out.println("Enter your first number."); 
      firstNumber = input.nextInt();
      input.nextLine();

      System.out.println("Enter your second number."); 
      secondNumber = input.nextInt();

      finalNumber = firstNumber % secondNumber;

      if(finalNumber !=0) {//If the remainder is not zero, these statements should be printed.
        System.out.println("Please enter even multiples.");     
      System.out.println("(Try switching the order in which you input the numbers)");
      } 
    }

/**
 * This is a while loop that will keep prompting the
 * user to enter two integers until the remainder
 * of the two integers is 0 and the two numbers
 * entered are even multiples.
 */
    while (finalNumber !=0);

    if(finalNumber == 0) {//The following code will be executed only if the remainder is 0.

      System.out.println("Displaying all odd numbers between " + firstNumber + " and " + secondNumber);

      int number = secondNumber;//Declaring number variable, giving it value of secondNumber.

/**
 * This is a while loop that will display all the odd
 * numbers between the two integers entered. 
 */
      while(number <= firstNumber){
        if (number % 2 != 0) {
          System.out.println(number);
        }
        number++;
      }
    }
    }

    catch (java.util.InputMismatchException e) { //Catching multiple exceptions.
     System.out.println("Please enter whole numbers.");
    }

    catch ( java.lang.ArithmeticException e) { //Catching multiple exceptions.
     System.out.println("Please enter whole numbers.");
    }


  } 
}

Answer 1

您在哪里执行此操作：

while (finalNumber !=0)

你可以这样做：

for (;finalNumber != 0;)

（当然，将条件放在循环的开头，因为for 没有do... while 等价物）而你在哪里这样做：

while(number <= firstNumber)

你可以这样做：

for (;number <= firstNumber;)

或者你可以合并一些语句，将两行代码移到循环条件中：

for (int number = secondNumber; number <= firstNumber; number++)

当然，这是否使代码更清晰或更富有表现力是一个见仁见智的问题。不清楚为什么要用for 替换while，但无论如何循环的结构是相同的。 for 在循环条件中只有两条语句的语法，一条用于启动循环，一条用于递增循环。终止条件完全相同。

---

旁注，这个 if 条件是多余的：

// ...
while (finalNumber !=0);
if(finalNumber == 0)
// ...

根据定义，当满足if 条件时，finalNumber 必须为0。紧接的前一行已经测试了该条件。您不需要两次测试相同的条件，运行时不会对 finalNumber 的值撒谎 :)