I need a help trying to set my code to continuously receive user input for factorial numbers. It will produce a question and intake the user input but only once. I want it to continue asking the user for that input.
I tried to do a while loop however nothing shows up.
import java.util.Scanner;
public class FactorialRecursion
{
public static void main(String[] arg)
{
Scanner scan = new Scanner(System.in);
long userInput;
System.out.println("Please enter a number you would like find the factorial of.");
userInput = scan.nextLong();
long fc = FactorialRecursion.fact(userInput);
System.out.println("Factorial = " + fc);
}
public static long fact(long x)
{
if (x <= 0)
return 1;
else
return FactorialRecursion.fact(x - 1) * x;
}
}
The output is correct but I want my program to continue asking for that input.
public class Test{
public static void main(String []args) {
int num;
Scanner scanner = new Scanner(System.in);
System.out.println("Enter numbers!");
while((num = scanner.nextInt()) > 0) {
System.out.println("Receiving...");
}
{
System.out.println("Negative number Stopping the system...");
System.exit(1);
}
}
}
Without knowing how you were looping before (my assumption is that you were including the scanner instantiation which might have caused an issue), here is an implementation that I believe will work for you. This will continue to scan for a number, unless a negative number is entered. Therefore you have an actual exit condition that doesn't make sense for factorial, and the user can repeatedly enter and find the factorial of positive numbers.
In order for this to work, I instantiated the userInput variable to be 0 so that the loop will run for the first time. You can alteratively use a do...While loop in stead, but I prefer this method generally.
public static void main(String[] arg)
{
Scanner scan = new Scanner(System.in);
long userInput=0;
while(userInput >=0)
{
System.out.println("Please enter a number you would like find the factorial of. Enter a negative number to exit.");
userInput = scan.nextLong();
long fc = FactorialRecursion.fact(userInput);
System.out.println("Factorial = " + fc);
}
}
If you would like to see what the do-while loop would look like, just comment and I'll put a little more time into answering this. Also any questions you have comment away!
Related
I want a program that repeatedly prompts the user to input a number and then prints whether that number is prime or not. This works once, then on the next iteration it gives a No Such Element Exception before the user can enter another input.
I've tried using IF statements with hasNext() or hasNextInt() but those never seem to be true for the same reason. I also tried using a FOR loop to iterate a fixed number of times but that gives the same error. Why is this allowing for user input the first time it loops through but not after that?
public static void primeChecker()
{
Scanner scan = new Scanner(System.in);
System.out.print("Please enter a number: ");
int number = scan.nextInt();
if (isPrime(number)) {
System.out.println(number + " is prime");
}
else {
System.out.println(number + " is not prime");
}
scan.close();
}
public static void main(String[] args)
{
int y=1;
while(y!=0)
{
primeChecker();
}
Remove scan.close();, as it is closing the scanner.
In order to repeatedly ask the user for a number without stopping, you need to put a while around the code.
Here is my take on this challenge:
public static void primeChecker() {
while(true) {
Scanner scan = new Scanner(System.in);
System.out.print("Please enter a number: ");
int number = scan.nextInt();
if (isPrime(number)) {
System.out.println(number + " is prime");
} else {
System.out.println(number + " is not prime");
}
}
}
public static void main(String[] args) {
primeChecker();
}
This code should repeatedly ask you for a number(after telling you what the previous answer was). It worked for me!
First of all what does your local variable have to do with the function? even if you pass it to function it won't change.
by looking at your code one thing you can do is safely remove y it has nothing to with it, and check in prime checker if number is equal to 0 System.exit(), this is one way to do it without changing much of this code.
while (true) {
primeChecker();
}
and inside primeChecker
int number = scanner.nextInt();
if (number == 0) {
System.exit(0);
}
it will terminate the programme when input is 0.
here you can learn more about System.exit:- https://www.baeldung.com/java-system-exit
I'm trying to learn (self-taught) Java by reading Big Java, Late Objects from by Cay Horstmann. I'm using repl.it to write my code (if you may want to look it up, it's public)
A selfcheck question of Chapter 4 Loops is:
How can you overcome the problem of when the user doesn't provide any input in the algorithm of section 4.7.5 (titled Maximum and Minimum) and the WHILE loop just terminates the program for this reason ?
They basically ask to rewrite the code so it solves this problem.
The information of section 4.7.5 you need to solve this problem: To compute the largest value in a sequence, keep a variable that stores the largest element that you have encountered, and update it when you find a larger one.
(This algorithm requires that there is at least one input.)
double largest = in.nextDouble();
while (in.hasNextDouble())
{
double input = in.nextDouble();
if (input > largest)
{
largest = input;
}
}
This is what the book suggests as the answer to this problem (but I disagree):
One solution is to do all input in the loop and introduce a Boolean variable that checks whether the loop is entered for the first time.
double input = 0;
boolean first = true;
while (in.hasNextDouble())
{
double previous = input;
input = in.nextDouble();
if (first) { first = false; }
else if (input == previous) { System.out.println("Duplicate input"); }
}
I don't fully understand the first sentence. And I disagree this as a solution for the problem because (as far as I can tell) it tests whether the input has been entered before, instead of testing if any sort of user input has been provided..
I tried to merge those two sections of code together but I can't seem to make it work. Or more specific: figure out how to build it. What variables / loops do I need? In which order do I write this?
I've made a flowchart in Visio of the first section of code but have no clue how to continue.
This is what I've written so far:
import java.util.Scanner;
class Main {
public static void main(String[] args)
{
Scanner input = new Scanner(System.in);
System.out.println("Enter the number: ");
double largest = 0;
while (input.hasNextDouble())
{
double value = input.nextDouble();
if (value > largest)
{
largest = value;
System.out.println("The largest input till now is: " + largest);
}
}
Can someone:
Ask me questions which help me to solve this question? I.e. Tell me what tools I need (WHILE, FOR etc.)
Provide a solution in text which I can hopefully transform in code
Or write the code for me (I haven't learned arrays yet, so please solve it without)
Thanks in advance,
So I worked on this for a bit and I think I have something close to what you're looking for using a do while loop.
This code accepts user input first, then checks it's value in comparison to the last input and return either "Input a higher value", "Duplicate number found", or it sets the last number entered to the current number.
I hope this helps you get your code to where you'd like it to be! I'm still new, so I apologize if this is not entirely optimized.
Also, I have not added a way to exit the loop, so you may want to add a check on each iteration to see if the user would like to continue.
public static void main(String[] args) {
double userInput = 0;
double prevNum = 0;
boolean hasValue = false;
boolean exitCode = false;
do {
Scanner sc = new Scanner(System.in);
System.out.println("Please enter a number: ");
userInput = sc.nextDouble();
do {
if (userInput<prevNum) {
System.out.println("Please enter a number higher than " + prevNum);
hasValue=true;
}
else if (userInput==prevNum) {
System.out.println("Duplicate input detected.");
hasValue=true;
}
else {
prevNum = userInput;
hasValue = true;
}
}
while(hasValue==false);
System.out.println(prevNum);
System.out.println(userInput);
}
while(exitCode==false);
}
If you want compute if the number entered is the largest entered from the beginning but declare it at the largest if it's the first iteration then do this :
import java.util.Scanner;
public class Main {
public static void main(String[] args) {
Scanner input = new Scanner(System.in);
boolean flag = true;
double largest = 0;
System.out.println("Enter the number: ");
while (input.hasNextDouble()){
double value = input.nextDouble();
if (flag) {
flag = false;
largest = value;
}
else if (value > largest) largest = value;
System.out.println("The largest input till now is: " + largest);
System.out.println("Enter a new number: ");
}
}
I am trying to read an integer from the user, then print even if that number is an even number or odd otherwise. I have been told I can assume that the user types a valid integer. The input/output should match the following example:
Type a number: 14
even
What am I missing? Any ideas on how I can get the desired inputs and expected outputs? Test1[3][Test4]4
import java.util.Scanner;
public class evenOdd {
public static void main(String[] args) {
// TODO Auto-generated method stub
Scanner scan = new Scanner(System.in);
int even = scan.nextInt();
int odd = scan.nextInt();
if ((even%2)==0){
System.out.println("Type a number:"+ even);
}
else {
System.out.println("Type a number:"+ odd);
}
}
}
The problem is that you have all your variables and order of the flow of your program mixed up. In English this is what you are doing
Prompt user for an integer, call that integer "even"
Prompt user for an integer, call that integer "odd"
If the integer called "even" is divisible by 2 without a remainder then print "type a number" and then the value of the integer called "even"
Otherwise print "type a number" and then the value of the integer called "odd"
You only need to read a value from the user once, then decide which message to print based on that value:
import java.util.Scanner;
public class evenOdd {
public static void main(String[] args) {
System.out.println("Type a number:");
Scanner scan = new Scanner(System.in);
int number = scan.nextInt();
if ((number%2)==0){
System.out.println("even");
}
else {
System.out.println("odd");
}
}
}
I have pointed out some issues in your code. Please correct them.
import java.util.Scanner;
//follow java naming convention and name class as "EvenOdd"
public class evenOdd {
public static void main(String[] args) {
Scanner scan = new Scanner(System.in);
int number = scan.nextInt(); //renamed to number
int odd = scan.nextInt(); //do not need this variable
if ((number %2)==0){
System.out.println("Even");
}
else {
System.out.println("Odd");
}
}
}
Ask the user the question first so that he knows he has to input a number
System.out.println("Type a number: ");
You can simply just get 1 input from the user and store on the same variable
int input = scan.nextInt();
Then you would just check that 1 input with the if/else and display the correct output
if ((input%2)==0){
System.out.println(input + " is even.");
}
else {
System.out.println(input + " is odd.");
}
import java.util.Scanner;
public class MyFirstGame {
public static void main(String[] args) {
Scanner scanner = new Scanner(System.in);
System.out.println("Please Enter A Number: ");
double s = scanner.nextDouble();
double randomNumber = Math.random();
double realNumber = randomNumber*10;
double realerNumber = Math.round(realNumber);
System.out.println(realerNumber);
if(s==realerNumber) {
System.out.println("You Win!");
} else {
System.out.println("Try Again...");
}
}
}
So what I am trying to do is make a "game" for my Java class. I have generate a random number between 1 and 10 and the user has to input a number and if the input and the random number are the same, they "win." If they lose, they try again...? First, I did all the necessary scanner stuff that I don't even fully understand. I just copied the professor. So the program says to enter a number and the program generates a number between 0.0 and 1.0. I multiply that number by 10 to make it between 1 and 10. Then I round the number to the nearest integer. If the input matches this number, the program says you win. If not, it'll say try again.
The problem is how do I make the program repeat itself without the user having to reboot the program with the cmd? I need to repeat the input, random number generator, and then the result. What do I need to do? Also, how is my program? My second big one...yeah right...big. But seriously, how can I make it less complex or anything to improve it. Thanks.
Use a while loop:
long realerNumber = Math.round(realNumber);
// first guess
long guess = scanner.nextLong();
while (guess != realerNumber) {
System.out.println("Try Again...");
// guess again
guess = scanner.nextInt();
}
System.out.println("You Win!");
There is already a class to generate random numbers, you could use it:
// TODO: move to constant
int MAX = 10;
// nextInt(int n) generates a number in the range [0, n)
int randomNumber = new Random().nextInt(MAX + 1)
just put your code inside the do-while loop
Scanner scanner = new Scanner(System.in);
do
{
System.out.println("Please Enter A Number: ");
double s = scanner.nextDouble();
double realerNumber = Math.round( Math.random() * 10 );
System.out.println(realerNumber);
if(s==realerNumber) {
System.out.println("You Win!");
} else {
System.out.println("Try Again...");
}
}
while(someCondition);
the someCondition can be for example a counter (if you want to play n times just set counter to n and decrease it every loop iteration then check if it is 0 in while) or some function checking if a key is pressed (like escape)
int n = 5;
do
{
n--;
...
}
while(n > 0);
This will run forever, but it's the idea mentioned in the first comment
...
Scanner scanner = new Scanner(System.in);
while(true){ // add this after Scanner ... declaration
...
} // end of existing else block
} // end of while loop, so add this single brace
...
I did see other questions like mine but my program was quite different so I couldn't figure out the problem. Basically, when I'm asked to enter code using this program, it needs to be entered twice. I can't figure out why.
Anyone know what I'm doing wrong? I'm sure it's something simple I'm missing.
package prac4;
import java.util.Scanner;
public class PrintNums {
public static void main(String[] args) {
int number=1;
Scanner sc = new Scanner(System.in);
System.out.println("What number should I count to?");
while (sc.nextInt()<0){
System.out.println("Please enter a positive integer: ");
if(sc.nextInt()>0){
number = sc.nextInt();
}
}
number = sc.nextInt();
sc.close();
System.out.println(number);
}
}
you are asking input 2 times (sc.nextInt()), so if you want to get the value once you should call sc.nextInt() once. you can change the snippet like below.
package prac4;
import java.util.Scanner;
public class PrintNums {
public static void main(String[] args) {
Scanner sc = new Scanner(System.in);
int number=sc.nextInt();
System.out.println("What number should I count to?");
while (number<0){
System.out.println("Please enter a positive integer: ");
number = sc.nextInt();
}
sc.close();
System.out.println(number);
}
}
Every time you call sc.nextInt() program hangs and waits for your input. You need to call sc.nextInt() only once and assign number only once per cycle and then check your condition:
while ((number = sc.nextInt()) < 0) {
System.out.println("Please enter a positive integer: ");
}
System.out.println(number);