CODEWITHSUNDEEP
javabluej
Kieran
Kieran

Reputation: 5

Stopping a repeating Println in a while loop, BlueJ

Below is the code I have so far, it is a calculator for my computer science class. The problem I am having is that on the second run of the program the System.out.print("Would you like to perform a calculation? (y/n) "); runs twice instead of once. I have already turned in the project, but I would like to know why it does this and how, in my future programs, I can fix it. I'll post the rest of the code below.

I appreciate all of your help, I credit the "A" that I got on it to all of you. Thanks! 

/**
* A calculator with multiple functions.
* @author () 
* @version (version 2.1)
*/
import java.io.*;
import java.util.Scanner;
public class Calc
{
  public static void main(String args[])
  {
    Scanner reader = new Scanner(System.in);
    String cont = "", funct = "";
    double fnum = 0, snum = 0, answer = 0;

    while(true)
    {
        System.out.print("Would you like to perform a calculation? (y/n) ");
        cont = reader.nextLine();
        if (cont.equalsIgnoreCase("y"))
        {
            System.out.println("What function would you like to do?");
            System.out.println("+?");
            System.out.println("-?");
            System.out.println("*?");
            System.out.println("/?");
            funct = reader.nextLine();
            if (funct.equals("+"))
            {
                System.out.println("Simple addition calculator");
                System.out.println("Enter first num: ");
                fnum = reader.nextDouble();
                System.out.println("Enter second num: ");
                snum = reader.nextDouble();
                answer = fnum + snum;
                System.out.println("Answer: " + answer);
                System.out.println(" ");
            }
            if (funct.equals("-"))
            {
                 System.out.println("Simple subtraction calculator");
                System.out.println("Enter first num: ");
                fnum = reader.nextDouble();
                System.out.println("Enter second num: ");
                snum = reader.nextDouble();
                answer = fnum - snum;
                System.out.println("Answer: " + answer);
                System.out.println(" ");
            }
            if (funct.equals("*"))
            {
                 System.out.println("Simple multiplication calculator");
                System.out.println("Enter first num: ");
                fnum = reader.nextDouble();
                System.out.println("Enter second num: ");
                snum = reader.nextDouble();
                answer = fnum * snum;
                System.out.println("Answer: " + answer);
                System.out.println(" ");
            }
            if (funct.equals("/"))
            {
                 System.out.println("Simple division calculator");
                System.out.println("Enter first num: ");
                fnum = reader.nextDouble();
                System.out.println("Enter second num: ");
                snum = reader.nextDouble();
                answer = fnum / snum;
                System.out.println("Answer: " + answer);
                System.out.println(" ");
            }
        }
        else if (cont.equalsIgnoreCase("n"))
        {
            break;
        }

    }
  }
}

Upvotes: 0

Views: 1002

Answers (4)

user5509117
user5509117

Reputation: 23

You need to consume the newline character after you call nextDouble() and before the next nextLine() to prevent nextLine() consume the newline character. Otherwise funct = reader.nextLine(); will take the new line character as input and not wait for any more user input, which results in the repeat.

if (funct.equals("/"))
            {
                System.out.println("Simple division calculator");
                System.out.println("Enter first num: ");
                fnum = reader.nextDouble();
                System.out.println("Enter second num: ");
                snum = reader.nextDouble(); // consume the new line character
                reader.nextLine();
                answer = fnum / snum;
                System.out.println("Answer: " + answer);
                System.out.println(" ");
            }

Upvotes: 2

mjlowky
mjlowky

Reputation: 1223

In all of your function conditions inside the loop, you are using reader.nextDouble(). This will only read the number (e.g "8") input not the new line (the enter) which is entered by the user after the number. Following code for the minus(-) function will not print "Would you like to perform a calculation? (y/n) " twice as the new line is already read. Here reader.nextLine() is used instead of reader.nextDouble(). reader.nextLine() will read the whole line not only the number.

if (funct.equals("-"))
        {
            System.out.println("Simple subtraction calculator");
            System.out.println("Enter first num: ");
            fnum = Double.parseDouble( reader.nextLine());
            System.out.println("Enter second num: ");
            snum = Double.parseDouble( reader.nextLine());
            answer = fnum - snum;
            System.out.println("Answer: " + answer);
            System.out.println(" ");
        }

Upvotes: 2

Abhishek kumar
Abhishek kumar

Reputation: 2676

Basically what is happening is when you are using the reader.nextLine() method, there is still a newline character left in the buffer, which is picked up when calling nextLine(). So it's making an extra run with the newline character. If you run your program with newline as the input even for the first time, it will loop without doing anything. So, you just need to clear out the buffer before going into your while loop.

Upvotes: 0

Kiran Indukuri
Kiran Indukuri

Reputation: 412

Try adding this reader.nextLine(); before the while loop ends, as mentioned below. This will clear the screen buffer.

else if (cont.equalsIgnoreCase("n")) { break; } reader.nextLine(); } Hope this helps,

Upvotes: 0

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