如何不为循环内的无效输入增加循环计数器

Question

我正在尝试编写一个简单的程序，该程序将使用扫描仪获取输入并输出最小数字、最大数字以及它们的平均值。但我不想要小于 0 或大于 100 的数字。我有程序输出最小值、最大值和平均值，它会告诉我输入的数字是小于 0 还是大于 100，但它仍然将其视为 for 循环中的“轮换”。我基本上希望程序在输入错误数字时返回到前一个数字，而不是在 for 循环中继续前进。有什么建议？ 谢谢！

import java.text.DecimalFormat;
import java.util.Scanner;
public class ExamGrades {

public static void main(String[]args){

    Scanner scan = new Scanner(System.in );

        int number = 0;
        double total = 0;
        int minimum;
        int maximum = 0;

        System.out.println("Please enter the first integer: ");

        number = scan.nextInt();
        minimum=number;
        total += number;

        for(int i = 2; i<11; i++){

            if(number<0 || number >100){
                System.out.println("Please enter a valid number: ");
                number = scan.nextInt();
            }
            else{
                System.out.println("Please enter integer " + i + ":");
                number = scan.nextInt();
                total += number;

            if(number<minimum)
                minimum = number;
            if(number>maximum)
                maximum = number;
            }
        }

        DecimalFormat oneDecimalPlace = new DecimalFormat("##.#");
        System.out.println("The minimum is: " + minimum);
        System.out.println("The maximum is: " + maximum);
        System.out.println("The average is: " + oneDecimalPlace.format((total) / 10.0 ));

    }
}

Answer 1

您可以从 for 循环内部递减循环计数器（变量 i）；这可能不是最佳做法，但它可以完成工作。

或者，您可以使用 while 循环（例如 while (i

Answer 2

考虑使用while() 而不是for()：

int i = 1;
while(i <= 10){
    if(number < 0 || number > 10) {
        // Code goes here
    } else {
        // More code goes here
        i++; // Notice that i only increments here
    }
}

其他选项是do... while() 循环，这可以帮助您避免重复代码：

int i = 1;
do {
    if(i == 1)
        System.out.print("\nEnter first number:\t");
    else
        System.out.print("\nEnter next number: \t");
    number = scan.nextInt();
    if(number < 0 || number > 10) {
        // Code goes here
    } else {
        // More code goes here
        i++; // Again, i only increments here
    }
} while(i < 10);

Answer 3

您可以将if 语句更改为while loop。

for(int i = 2; i < 11; i++){
    System.out.println("Please enter integer " + i + ":");
    number = scan.nextInt();

    while(number < 0 || number > 100){ // Wait for valid input
        System.out.println("Please enter a valid number: ");
        number = scan.nextInt();
    }

    total += number;
    if(number < minimum) minimum = number;
    if(number > maximum) maximum = number;
}

这样，在有有效输入之前，您不会在 for loop 中进行另一次迭代。

Answer 4

把它写成一个while循环

import java.text.DecimalFormat;

import java.util.Scanner;

public class ExamGrades {

public static void main(String[]args){

    Scanner scan = new Scanner(System.in );

    int number = 0;
    double total = 0;
    int minimum;
    int maximum = 0;
    int I = 2;
    System.out.println("Please enter the first integer: ");

    number = scan.nextInt();
    minimum=number;
    total += number;

    while (I < 11){

        if(number<0 || number >100){
            System.out.println("Please enter a valid number: ");
            number = scan.nextInt();
        }
        else{
            System.out.println("Please enter integer " + i + ":");
            number = scan.nextInt();
            total += number;

            if(number<minimum)
                minimum = number;
            if(number>maximum)
                maximum = number;
            I++;
            }
        }

        DecimalFormat oneDecimalPlace = new DecimalFormat("##.#");
        System.out.println("The minimum is: " + minimum);
        System.out.println("The maximum is: " + maximum);
        System.out.println("The average is: " + oneDecimalPlace.format((total) / 10.0 ));

    }
}