How to add within a while loop in java?

Question

Thank you for looking at my code. I am learning java and have run into an issue that is driving me crazy.

/*
 * The loop reads positive integers from standard input and that
 * terminates when it reads an integer that is not positive. After the loop
 * terminates, it prints out, separated by a space and on a single line, the
 * sum of all the even integers read and the sum of all the odd integers
 */

The thing is that the variables are not adding! I know my syntax is good. I think there something about the java language that I don't understand with how loop works and adds.

import java.util.Scanner;

class Testing2 {
    public static void main(String[] args) {
        int sumP = 0;
        int sumO = 0;

        Scanner stdin = new Scanner(System.in);

        System.out.println("Enter a positive or negative integer: ");

        while ((stdin.nextInt()) >= 0) {
            if (stdin.nextInt() % 2 == 0)
                sumP += stdin.nextInt();
            else
                sumO += stdin.nextInt();
        }
        System.out.println(sumP + " " + sumO);
        stdin.close();

    }
};

Are you sure? Why not add few System.out.println() statements to trace out execution? — kosa
– kosa, Commented Sep 30, 2013 at 4:28

sreisman · Accepted Answer · 2013-09-30 04:41:37Z

3

Every time you call stdin.nextInt() it is looking for another integer. To avoid this, at the top set a variable equal to the input:

int myInt = stdin.nextInt();

if (myInt >= 0) {
 if (myInt % 2 == 0)
                sumP += myInt;
            else
                sumO += myInt;
        }
        System.out.println(sumP + " " + sumO);
        stdin.close();

    }
}

You do not put the semicolon after the last curly brace as well. If you are expecting multiple numbers to be input you can continually check for the next it with,

while(stdin.hasNext()){
int myInt = stdin.nextInt();
}

edited Sep 30, 2013 at 4:41

answered Sep 30, 2013 at 4:33

sreisman

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4 Comments

Fred Larson Over a year ago

I think you meant to replace a few more of those nextInt() calls with myInt, didn't you?

sreisman Over a year ago

Yes sorry, edited it to use the variable instead of stdin.nextInt()

user2101421 Over a year ago

import java.util.Scanner; class Testing2 { public static void main(String[] args) { int sumP = 0; int sumO = 0; System.out.println("Enter a positive or negative integer: "); Scanner stdin = new Scanner(System.in); while (stdin.hasNext()) { int myInt = stdin.nextInt(); if (myInt >= 0) { if (myInt % 2 == 0) sumP += myInt; else sumO += myInt; } System.out.println(sumP + " " + sumO); } stdin.close(); } };

user2101421 Over a year ago

Thank you for your time. Your help definitely helped!

user2339071 · Accepted Answer · 2013-09-30 04:42:13Z

1

I think this solves the problem,

Scanner stdin = new Scanner(System.in);
while(1)
{
int num = stdin.nextInt();
if(num<0)
{
     stdin.close();
     break;
}
else
{
  if(num%2==0)
  {
  //Initialize sumP and sumO to 0
  sumP=sumP+num;
  }
  else
  {
  sumO=sumO+num;
  }
}
//You can now output sumP and sum) outside the loop safely.
}

answered Sep 30, 2013 at 4:42

user2339071

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Comments

Md. Abdul Bari · Accepted Answer · 2013-09-30 04:58:31Z

1

The problem is that you are using nextInt() every time. Use like this-

import java.util.Scanner;

class Testing2 {
    public static void main(String[] args) {
        int sumP = 0;
        int sumO = 0;

        Scanner stdin = new Scanner(System.in);

        System.out.println("Enter a positive or negative integer: ");
        int temp;
        while ((temp=stdin.nextInt())>0) {
            if (temp % 2 == 0)
                sumP += temp;
            else
                sumO += temp;
        }
        System.out.println(sumP + " " + sumO);
        stdin.close();

    }
}

answered Sep 30, 2013 at 4:58

Md. Abdul Bari

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Comments

Aurand · Accepted Answer · 2013-09-30 04:34:58Z

0

while ((stdin.nextInt()) >= 0) {
    if (stdin.nextInt() % 2 == 0)
       sumP += stdin.nextInt();
    else
       sumO += stdin.nextInt();
}

Your problem is that you're reading in 3 numbers each time you loop. Store the result of your read and then decided what to do with it, don't discard it and read 2 more numbers.

int nextInt;
while ((nextInt = stdin.nextInt()) >= 0) {
    // Do things with nextInt
}

answered Sep 30, 2013 at 4:34

Aurand

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Comments

chaser · Accepted Answer · 2013-09-30 04:42:47Z

0

I think you want to need coding like this

import java.util.Scanner;

class TestScaner {
public static void main(String[] args) {
    int sumP = 0;
    int sumO = 0;
    Scanner stdin = null;
    while (true) {
        stdin = new Scanner(System.in);

        System.out.println("Enter a positive or negative integer: ");

        int num = stdin.nextInt();

        if (num % 2 == 0)
            sumP += num;
        else
            sumO += num;

        System.out.println("==" + sumP + " " + sumO);

    }

}

};

answered Sep 30, 2013 at 4:42

chaser

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Comments

Luxknight007 · Accepted Answer · 2013-09-30 05:53:46Z

0

Please try these code

import java.util.Scanner;

class Testing2 {
    public static void main(String[] args) {
    int sumP = 0;
    int sumO = 0;
    int scn = 0;

    Scanner stdin = new Scanner(System.in);

    System.out.println("Enter a positive or negative integer: ");

    scn = stdin.nextInt();
   while (scn >= 0) {

       System.out.println("stdin next " + scn);
        if (scn % 2 == 0){
            sumP += scn;
        }else{
           sumO += scn;
        }
       scn--;
    }
    System.out.println(sumP + " " + sumO);


   }
};

your stdin.nextInt() does not decrease it only return a value of your stdin that is why it doesn't loop properly.

answered Sep 30, 2013 at 5:53

Luxknight007

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Comments

elune · Accepted Answer · 2013-09-30 06:05:55Z

0

u also should put scanner inside while:

 do {
 Scanner stdin = new Scanner(System.in);
            if (stdin.nextInt() % 2 == 0)
                sumP += stdin.nextInt();
            else
                sumO += stdin.nextInt();
        }while ((stdin.nextInt()) >= 0)

edited Sep 30, 2013 at 6:05

answered Sep 30, 2013 at 4:30

elune

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2 Comments

Piro Over a year ago

This will not even compile. You cannot define stdin twice. Also this is not a solution of problem

elune Over a year ago

yeah. what i want to say is scanner must put inside loop.

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