为什么我的程序在计算偶数时会忽略零？

Question

I'm having an issue when trying to count the number of even integers.

This is the code I'm working with:

int input=0, numeven=0;
Scanner scan = new Scanner(System.in);

input = scan.nextInt();

while (input != 0)
{
    //calculates the total number of even integers
    if (input%2 != 1)
    {
        numeven = numeven+1;
    }
}

I don't know how to set up the while loop: while (input! = 0)

Given the test input 6, 4, -2, 0 it says that I have three even numbers, but the expected outcome is 4 (because 0 is even).

Answer 1

If you want your loop to work on zero, and treat it as the exit mark too, switch from while to do / while :

do {
    input = scan.nextInt();
    //calculates the total number of even integers
    if (input%2 != 1)
    {
        numeven = numeven+1;
    }
} while (input != 0);

This way your code will process zero along with regular inputs, and stop reading further input upon reaching the end of the loop.

Answer 2

You don't want the loop to break when the user enters a 0 or any other integer incase you want to put 0 multiple times.

int numeven=0;
Scanner scan = new Scanner(System.in);

while (true) {
    String input = scan.next();
    try {
        int val = Integer.parseInt(input);
        if (val % 2 == 0)
            numeven++;

    } catch (NumberFormatException e) {
        //enter any input besides an integer and it will break the loop
        break;
    }
}

System.out.println("Total even numbers: " + numeven);

Alternatively this does the same thing. Except it won't consume the last value.

int numeven=0;
Scanner scan = new Scanner(System.in);

while (scan.hasNextInt()) {
    int val = scan.nextInt();
    if (val % 2 == 0)
        numeven++;
}

System.out.println("Total even numbers: " + numeven);

Answer 3

Just make the condition of your while loop to be

while( scan.hasNextInt() )

Then it will only loop as long as there are numbers. Inside the loop you can

input = scan.nextInt()