检查有效整数

Question

我目前正在编写一个程序 (java)，询问用户他们的 class 时间表，以及每个 class 有多少学分。学分的唯一有效答案应该是 1、2、3 或 4。我如何检查以确保这些是唯一有效的答案？如果他们输入的金额无效，我希望它循环并提示他们提出完全相同的问题。这是我目前所拥有的。

//Jake Petersen
import java.util.Scanner;
public class test{
  //I promise not to make all methods static in CS1
  public static void main(String[] args){
    Scanner scan = new Scanner(System.in);
    System.out.println("How many courses are you going to list?");
    int courses = Integer.parseInt(scan.nextLine());
    String courseArray[] = new String[courses];
    for (int i = 0; i < courseArray.length; i++){
      System.out.println("Please enter a course:");
      courseArray[i] = scan.nextLine();
    }
    int creditArray[] = new int[courses];
    for (int i = 0; i < creditArray.length; i++){
      System.out.println("Please enter how many credits " + courseArray[i] + " is:");
      creditArray[i] = scan.nextInt();
    }
    int sum = 0;
    for (int i : creditArray){
      sum += i;
    }
    for (int i = 0; i < courseArray.length; i++) {
      System.out.print(courseArray[i] + " is a " + creditArray[i] + " credit class. \n");
    }
    print(sum);
  }
  public static void print(int sum){
    if(sum >= 12 && sum <= 18){
      System.out.println("You are taking " + sum + " total credits, which makes you a full time student.");
    }else if(sum < 12){
      System.out.println("You are taking " + sum + " total credits, which makes you not a full time student.");
    }else{
      System.out.println("You are taking " + sum + " total credits, which means you are overloaded"); 
    }
  }
}

Answer 1

你必须这样做。

Scanner scan = new Scanner(System.in);
boolean a = true;
do{
   System.out.println("Insert your Value:");
   int value = scan.nextInt();
   if(value==1||......)a=false;
}while(a);

您可以将此部分插入到您的代码中。它将再次询问

Answer 2

作为替代方案，您可以简单地将增量从循环中拉出，如果输入有效则只增加 i，如下所示：

for (int i = 0; i < creditArray.length;) {
    System.out.println("Please enter how many credits "+ courseArray[i] + " is:");
    int input = scan.nextInt();
    if (input >= 1 && input <= 4) {
        creditArray[i++] = input; 
    }
}

Answer 3

您可以使用 while 循环和布尔变量来检查状态

    int creditArray[] = new int[courses];

    for (int i = 0; i < creditArray.length; i++) {
        boolean isValid = true;
        while(isValid)
        {
            System.out.println("Please enter how many credits " + courseArray[i] + " is:");
            int buffer =  scan.nextInt();               
            if(buffer == 1|| buffer == 2||buffer == 3||buffer==4)
            {
               isValid = false;
               creditArray[i] = buffer;
            }
        }

第二种方法是使用像这样的 do-while 语句：

boolean isValid = true;
do{
   System.out.println("Please enter how many credits " + courseArray[i] + " is:");
   int buffer = scan.nextInt();
   if(buffer == 1|| buffer == 2||buffer == 3||buffer==4)
   {
      a=false;
   }
   }while(a);

检查有效整数

Checking for Valid Integer

java

integer