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Issue with flow of a program

I am new to Java and just learning the basics.
I have gone through if checks/statements(if-if-if; if-else if-else, if-else), while and for loops as well. I have an assignment which I can not for the life of me figure out. I am having some issues with the flow of the program itself and I just get it to work half way through in Eclipse.
The idea of the program is for it to accept three integers from the keyboard(keyboard input using Scanner) and print out all numbers, between 0 and the first integer from the input, which can be divided by the second and third input integers, respectively. The first input integer has to be between 200 and 100. I will provide what code I have written. I can get the program to accept input but then I get the message in the console.
I set up the three integers, I set up a condition for the first integer using a while loop and then I use a for loop to print all the numbers between 0 and the first input integer. Then within the for loop I do in if check and print out all the numbers. It accepts the input three times but then I just goes to terminated status.
package Javawork;
import java.util.Scanner;
public class Test {
private static Scanner keyboard;
public static void main(String[] args) {
firstProgramme();
}
public static void firstProgramme() {
keyboard = new Scanner(System.in);
System.out.println("Enter number: ");
int firstNum = keyboard.nextInt();
int secondNum = keyboard.nextInt();
int thirdNum = keyboard.nextInt();
while (firstNum > 100 && firstNum < 200) {
for (int i = 0; i <= firstNum; i++) {
if (i % secondNum == 0 && i % thirdNum == 0) {
System.out.println(i);
}
}
}
}
}

As per your requirement you need to check whether the first number is between 100 and 200. For that you should use
if(firstNum > 100 && firstNum < 200) {
instead of
while(firstNum > 100 && firstNum < 200) {
As if will check the condition and while will iterate based on condition.

What is the proper way to prevent a program from exiting after a user enters wrong input in Java?

The Task
Design and implement an application that reads an integer value and prints out the sum of all EVEN integers between 2 and its input value, inclusive. Print an error message if the input value is less than 2. Prompt accordingly.
Note: the lesson was on while loops, not other loops such as for loop etc
The Issue
I have everything working, however something about how I have written this feels wrong. I currently have a while loop while(programOn) to keep the program running. without this while loop, if the user enters a number < 2, the user is asked to try again, however if the user tries again, the program exits instead of running the new input into the program. So, I created the while loop to force the program open until the user types an acceptable input.
- something about this feels hacky and incorrect i would really appreciate some validation on my method.
public static void main(String[] args){
int inputNumber;
int sum = 0;
boolean programOn = true;
Scanner scan = new Scanner(System.in);
System.out.println("Please Type a number no smaller than 2");
inputNumber = scan.nextInt();
//include the original input to sum
sum = inputNumber;
while(programOn){
if(inputNumber < 2){
System.out.println("you need a number greater than or equal to 2, try again");
inputNumber = scan.nextInt();
sum = inputNumber;
}else{
//from the number chosen divide until you reach 0
while(inputNumber != 0){
//subtract one from the number
inputNumber = (inputNumber - 1);
if((inputNumber % 2 == 0) && (inputNumber != 0)){
System.out.println(inputNumber);
//add the input to the sum
sum += inputNumber;
}
}
System.out.println("The sum is " + sum);
programOn = false;
}
}
}

That's because the validation is done by an if condition. What you need here is a while loop that keeps asking for inputs as long as user's input is less than 2, below is the code snippet that does this:
Scanner scan = new Scanner(System.in);
System.out.println("Please Type a number no smaller than 2");
int inputNumber = scan.nextInt();
while(inputNumber < 2){
System.out.println("you need a number greater than or equal to 2, try again");
inputNumber = scan.nextInt();
}
System.out.println(inputNumber);

java while loop won't print the text after a the stopping condition [closed]

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I just started studying Java and I'm required to use while to decided how many players can be goalkeepers based on their number. The loop is supposed to stop after the user entered 0 and print the counted number of players that can be goalkeepers.
public class Q3_201303719 {
public static void main(String[] args) {
Scanner input = new Scanner (System.in);
int num; int count=0;
System.out.println("Enter the players' numbers");
num = input.nextInt();
while ((num != 0) && (num < 31) && (num%2==0) || (num%3==0))
count++;
System.out.println(count+ " players can be goalkeepers.\n");
// Above line should be printed once the user enter 0, but in my case it won't
// print and keeps asking the user to enter a number.
}
}

From the question it is difficult to understand what it is you are trying to achieve. However, we can try to help you understand the code as it is written.
The while loop is currently written as:
while ((num != 0) && (num < 31) && (num%2==0) || (num%3==0))
This could be rewritten as the following and it would not make any difference:
while (num != 0 && num < 31 && num%2==0 || num%3==0)
The additional parenthesis that you included are not required.
In Java the operator precedence is && before ||. This means that the && operators will be evaluated first, followed by the ||. Therefore, the above statement could therefore be rewritten as the following and it would not make any difference:
while ((num != 0 && num < 31 && num%2==0) || num%3==0)
However, it may make the code a little easier to understand.
So when the code executes the following occurs:
The count variable is initialised to 0.
A value is retrieved and stored in the variable num. Lets say that this value is 10.
The while statement is evaluated for the first time:
num != 0 is true as 10 != 0.
num < 31 is true as 10 is less than 31.
num%2==0 is true as 10 divided by 2 is 5 and leaves a remainder of 0.
As these all evaluate to true, the OR part (num%3==0) is not evaluated as it is not neccessary. See short circuit evaluation (http://users.drew.edu/bburd/JavaForDummies4/ShortCircuitEval.pdf).
The count is incremented to 1.
The loop executes again for the second time. num is still 10.
num != 0 is true as 10 != 0.
num < 31 is true as 10 is less than 31.
num%2==0 is true as 10 divided by 2 is 5 and leaves a remainder of 0.
The count is incremented to 2.
And so on... in an infinite loop.
If the variable num was instead set to 9. The loop would evaluate as follows:
num != 0 is true as 9 != 0.
num < 31 is true as 9 is less than 31.
num%2==0 is false as 9 divided by 2 is 4 and leaves a remainder of 1.
Therefore, now the || part is evaluted:
num%3==0 is true as 9 divided by 3 is 3 and leaves a remainder of 0.
Again, this would result in an infinite loop.
If the variable num was instead 0:
num != 0 is false
As the first num!=0 is false, the num<31 and num%2==0 parts are not evaluated as their results would not make any difference.
The num%3==0 is then evaluated:
num%3==0 is true as 0 divided by 3 leaves a remainder of 0.
Again, this would result in an infinite loop.
I hope that this may help to clarify your understanding and allow you to correct the code appropriately.

how many players' numbers do you have to input?
you have a while loop that depends on num value, but you never change the num value. that will end up in endless loop...
if you have more players, create a for loop to enter the numbers, store the numbers in an array or an arraylist and if you use the while loop, use it so that it depends on a value that you change inside the loop. otherwise it will loop forever.
do{
System.out.println("Enter the players' numbers");
num = input.nextInt();
count++;
}while(num!=0);
your code with this should look like this:
public static void main(String[] args) {
Scanner input = new Scanner(System.in);
int num;
int count = 0;
do {
System.out.println("Enter the players' numbers");
num = input.nextInt();
count++;
} while (num != 0);
System.out.println(count + " players can be goalkeepers.\n");
// Above line should be printed once the user enter 0, but in my case it
// won't
// print and keeps asking the user to enter a number.
}

If you can't use a do-while-loop as Ubica suggested, then you need to work your way around it:
public static void main(String[] args) {
Scanner input = new Scanner(System.in);
int num=2; // you need to initialize num with a value, that allows you to go inside the while loop at least once
int count = 0;
while((num != 0) && (num < 31) && (num % 2 == 0) || (num % 3 == 0)) {
System.out.println("Enter the players' numbers");
num = input.nextInt(); // user input is here inside the loop
count++; // your count will count every valid input + the user input that ends the loop
}
count--; // if your user entered 0 to exit the loop, count would have still incremented, so you need do subtract one again
System.out.println(count + " players can be goalkeepers.\n");
}
As I commented in the code, first you initialize num with a dummy value, that allows you to enter the loop at least once. Then you listen to the users input and count the loop iterations. But since the loop will execute at least once (even though your user might enter 0 right away to exit the loop) your count would be one higher than the actual number of valid inputs. So you have to subtract that 1 from your count again.
EDIT
I forgot to mention: your loop will not stop when the user enters 0 because
(num % 3 == 0) // is true with num=0
so when the user enters 0 the while condition will evaluate like this:
while( false && true && true || true )
while( false || true )
while( true )

The bracketing for the loop should fix this problem.

You need braces surrounding your while loop block. As a general rule, it is best to overuse braces rather than under-use them.
Your code should look like:
package q3_201303719;
import java.util.Scanner;
public class Q3_201303719 {
public static void main(String[] args) {
Scanner input = new Scanner (System.in);
int num; int count=0;
System.out.println("Enter the players' numbers");
num = input.nextInt();
while((num != 0) && (num < 31)&& (num%2==0)|| (num%3==0)) {
count++;
}
// The braces added above are required for the while loop and will keep your program
// from not outputting your results.
System.out.println(count+ " players can be goalkeepers.\n");
}
}
Best of luck and happy coding. :)

Your code isn't making sense.
1st : The While loop is not modifying the "num" value, resulting in
infinite loop if entered.
2nd : What is the code supposed to do? It is really hard to tell from what you show.
I think placing while loop upper could help you, but still code makes no much sense
public class Q3_201303719 {
public static void main(String[] args) {
int num = 0; int count=0;
while((num != 0) && (num < 31)&& (num%2==0)|| (num%3==0)) {
Scanner input = new Scanner (System.in);
System.out.println("Enter the players' numbers");
num = input.nextInt();
count++;
}
System.out.println(count+ " players can be goalkeepers.\n");
// Above line should be printed once the user enter 0, but in my case it won't
// print and keeps asking the user to enter a number.
}
}
Edit :
This problem occurred because you didn't follow a really simple rule : think before coding.
For this exercise you need to think about what your code should be doing, and then write the code for it. Coding is just a language, if you know what you want to write then it is easier. Here you obviously don't really know what you wanna do, and as you are new with development it was likely that you get stucked

java program outputting even/odd numbers

My task is to write a java program that first asks the user how many numbers will be inputted, then outputs how many odd and even numbers that were entered. It is restricted to ints 0-100. My question is: What am I missing in my code?
import java.util.Scanner;
public class Clancy_Lab_06_03 {
public static void main(String[] args) {
Scanner input = new Scanner(System.in);
int n;
System.out.println("How many numbers will be entered?");
n = input.nextInt();
while (n < 0 || n > 100) {
System.out.println("ERROR! Valid range 0-100. RE-Enter:");
n = input.nextInt();
n++;
}
int odd = 0;
int even = 0;
while (n >= 0 || n <= 100) {
n = input.nextInt();
if (n % 2 == 0) {
even++;
} else {
odd++;
}
}
System.out.println(even + "even" + odd + "odd");
}
}

Second while loop is infinite. Relplace it with something like this:
for (int i = 0; i < n; i++) {
int b = input.nextInt();
if (b % 2 == 0) {
even++;
} else {
odd++;
}
}
Also I don't understand why are you incrementing n in first loop. For example when you will first give -5, you will be asked to re-enter the number. Then you type -1, but it gets incremented and in fact program processes 0, altough user typed -1. In my opinion it is not how it suppose to work and you should just remove this n++.
As you asked in comment - the same using while loop:
while(n > 0) {
n--;
int b = input.nextInt();
if (b % 2 == 0) {
even++;
} else {
odd++;
}
}
Also it is good idea to close input when you no longer need it (for example at the end of main method)
input.close();

You had two issues - first you were incrementing n in the first loop, rather than waiting for the user to enter a valid number.
In the second loop, you weren't comparing the number of entries the user WANTED to make with the number they HAD made - you were over-writing the former with the new number.
This version should work, although I've not tested it as I don't have java on this machine.
Note that we now sit and wait for both inputs, and use different variable names for the "how many numbers will you enter" (n) and "what is the next number you wish to enter" (num) variables? Along with a new variable i to keep track of how many numbers the user has entered.
import java.util.Scanner;
public class Clancy_Lab_06_03
{
public static void main (String[] args)
{
Scanner input = new Scanner (System.in);
int n;
System.out.println ("How many numbers will be entered?");
n = input.nextInt();
//Wait for a valid input
while (n < 0 || n > 100)
{
System.out.println ("ERROR! Valid range 0-100. RE-Enter:");
n = input.nextInt();
}
//Setup variables for the loop
int odd = 0;
int even = 0;
int num;
//Keep counting up until we hit n (where n is the number of entries the user just said they want to make)
for(int i = 0; i < n; i++)
{
//Changed this, because you were over-writing n (remember, n is the number of entries the user wants to make)
//Get a new input
while (num < 0 || num > 100)
{
System.out.println ("ERROR! Valid range 0-100. RE-Enter:");
num = input.nextInt();
}
//Check whether the user's input is even or odd
if (num % 2 == 0)
{
even++;
}
else
{
odd++;
}
}
System.out.println(even + " even. " + odd + " odd.");
}
}

import java.util.Scanner;
public class Test2 {
public static void main(String[] args) {
System.out.println("Enter an Integer number:");
Scanner input = new Scanner(System.in);
int num = input.nextInt();
if ( num % 2 == 0 )
System.out.println("Entered number is even");
else
System.out.println("Entered number is odd");
}
}

My suggestion to you is to have a clear separation of your requirements. From your post, you indicate you need to prompt the user for two distinct data items:
How many numbers will be entered (count)
The values to be analyzed
It is a good practice, especially when you are learning, to use meaningful names for your variables. You are using 'n' for a variable name, then reusing it for different purposes during execution. For you, it is obvious it was difficult to figure out what was 'n' at a particular part of the program.
Scanner input = new Scanner (System.in);
int count;
System.out.println ("How many numbers will be entered?");
count = input.nextInt();
//Wait for a valid input
while (count < 1 || count > 100)
{
System.out.println ("ERROR! Valid range 1-100. RE-Enter:");
count = input.nextInt();
}
Additionally, a count of zero should not be valid. It does not make sense to run a program to evaluate zero values (don't bother a program that does nothing). I believe the lowest count should be one instead.
int odd = 0;
int even = 0;
int value;
do
{
System.out.print("Enter a number between 0 and 100: ");
value = input.nextInt();
while (value < 0 || value > 100)
{
System.out.println ("ERROR! Valid range 0-100. RE-Enter:");
value = input.nextInt();
}
if (value % 2 == 0)
{
even++;
}
else
{
odd++;
}
count--; // decrement count to escape loop
} while (count > 0);
System.out.println(even + " even. " + odd + " odd.");
This example uses a do/while loop because in this case, it is OK to enter the loop at least once. This is because you do not allow the user to enter an invalid number of iterations in the first part of the program. I use that count variable directly for loop control (by decrementing its value down to 0), rather than creating another variable for loop control (for instance , 'i').
Another thing, slightly off topic, is that your requirements were not clear. You only indicated that the value was bounded to (inclusive) values between 0 and 100. However, how many times you needed to repeat the evaluation was not really clear. Most people assume 100 was also the upper bound for your counter variable. Because the requirement is not clear, checking a value greater or equal to 1 for the count might be valid, although highly improbable (you don't really want to repeat a million times).
Lastly, you have to pay attention to AND and OR logic in your code. As it was indicated, your second while loop:
while (n >= 0 || n <= 100) {}
Is infinite. Because an OR evaluation only needs one part to evaluate to TRUE, any number entered will allow the loop to continue. Obviously, the intent was not allow values greater than 100. However, entering 150 allows the loop to continue because 150 >= 0. Likewise, -90 also allows the loop to continue because -90 <= 100. This is when pseudocode helps when you are learning. You wanted to express "a VALUE between lower_limit AND upper_limit." If you reverse the logic to evaluate values outside the limit, then you can say " value below lower_limit OR above upper_limit." These pseudocode expressions are very helpful determining which logical operator you need.
I also took the liberty to add a message to prompt the user for a value. Your program expects the user to enter two numbers (count and value) but only one prompt message is provided; unless they enter an out of range value.

extract even numbers from arrayList
ArrayList numberList = new ArrayList<>(Arrays.asList(1,2,3,4,5,6));
numberList.stream().filter(i -> i % 2 == 0).forEach(System.out::println);

Unsure what the issue is

I'm really new to this whole programming thing, and I'm trying to wrap my head around why the loop ends abruptly and does not continue to the final if statement. Can you guys help me figure out whats wrong?
import java.util.Scanner;
public class FunnyAverage {
public static void main(String[] args) {
Scanner in = new Scanner(System.in);
System.out.print("How many values to read? ");
int top = in.nextInt();
System.out.print("Enter Value: ");
int one = in.nextInt();
int number = 1;
int sum = 0;
sum = sum + one;
while (number <= top) {
if (one % 6 != 0 && one % 17 != 0) {
System.out.print("Enter Value: ");
one = in.nextInt();
number++;
} else if (one % 6 == 0 && one % 17 == 0) {
System.out.print("Enter Value: ");
one = in.nextInt();
number++;
}
}
if (sum / top != 0) {
System.out.print("Average: " + sum / top);
}
System.out.print("None Divisible");
}
}

The final if() condition executes if you give the right input values. I ran your code and gave the below inputs to execute the final if() statement.
How many values to read? 1
Enter Value: 1
Enter Value: 1
Average: 1None Divisible
I dont understand what are you trying in the code, but there are many things missing like i assume you want to capture the sum of the input numbers, but sum is not used in the while loop.

Looks like you end up in the non-present else case (within the while loop). Consequently, number isn't increased and you are stuck in the while loop.
Try reading one within the while loop. This way the user will be prompted to enter a new number in each loop.
Otherwise you will be stuck in the while loop once the user enters a number that isn't conform with your checks.