如何打破while循环Java

Question

My code runs smoothly in eclipse but when I run it at codezinger , an online website to submit code it gives error such as Exception in thread "main" java.util.NoSuchElementException at this line char character = sc.next().charAt(0); at the main class . and input mismatched at line double pay=sc.nextDouble(); at the main class. I really dont know why as my code runs perfectly at eclipse.

this is picture of my code runs. enter image description here

the input at codezinger;

5  
=  
- 0.70  
- 2.40   
- 1.20   
+ 20.00   
3  
- 5.00   
- 0.50    
=    
0

main class;

import java.text.DecimalFormat;
import java.util.Scanner;
public class TestMyPrintCard {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int x=1;
        DecimalFormat df = new DecimalFormat("0.00");
        int N = sc.nextInt();
        sc.nextLine();
        do {
        System.out.println("Case #" + x + ":");
        MyPrintCard c1 = new MyPrintCard(); 
        for(int i=0; i<=N; i++) {
        char character = sc.next().charAt(0); // char input =,+,- // the problem here
            
        if (character=='=' ) {
            System.out.print("RM");
            System.out.println(df.format(c1.getBalance()));
            
            
        } else if (character=='+') {        
            double topup=sc.nextDouble();
             c1.topupCard(topup);
             
            
        }else if (character=='-') {
            double pay=sc.nextDouble(); // problem  here
            c1.payService(pay);             
        }   
        }//end for  
        x++;
        } while(N!=0);  
    }
    }

the class;

import java.text.DecimalFormat;
public class MyPrintCard {
    private double balance; //declare
    DecimalFormat df = new DecimalFormat("0.00");
    
    MyPrintCard(){ //constructor initialised
        balance = 10.00;        
    }
    
    //getter
    public double getBalance() {
        return balance;
    }
    
    public void topupCard(double amt) {
        
        balance += amt;
        System.out.print("RM");
        System.out.println(df.format(balance));         
    }
    
    public void payService(double amt) {    
        if(balance>5 ) {
            balance -= amt;
            System.out.print("RM");
            System.out.println( df.format(balance));                    
        }  
        else        
            System.out.println("invalid");
    }   
}

Answer 1

You're either lying or you're no good at testing. For example, the very example input you pasted wouldn't work, even in eclipse.

Your do/while loop runs forever . It has no stop condition at all: No break, and the while condition of N != 0 will never fail to be true , as you never modify N . Your error is that you're supposed to re-read N at the top of that do loop, instead of before it. Every segment in the input starts with a number indicating how many operations follow (with 0 being used to terminate the app). You only read the first such number.

Fix that and this code will work fine... probably, there is one more small issue:

Separately, that sc.nextLine() is not useful to this code and dangerous in that it can mess with reading the input depending on precisely how codezinger is providing it to you. Note that a very large amount of tutorials on scanner and keyboard input out there, including most SO answers, erroneously suggesting you run sc.nextLine() after every input. Do not do this ¹ .

1. Not relevant to this question, but I better back up such a statement: If you want keyboard input where hitting enter separates input, instead configure the scanner properly (use scanner.useDelimiter("\\\\R") , call scanner.next() to get a line of text, and don't ever call .nextLine() ). This is much simpler (no need to remember to toss those pointless nextLine() in there) can read blank input, and will not fail if the user tries to separate things with spaces instead of newlines.