I created a program that enables you to type in four numbers that must have specific requirements:
-must be a multiple of 4 or 6
-if greater than 500, must be a multiple of 10
The program takes the four numbers and gives you the sum of them, the average of them, shows you the smallest of the four numbers and finally the largest of the four numbers.
Now I want to try and display a group that each number belong to. I want these groups if you were wondering:
Group Tens if the number is between 0 and 99
Group Hundreds if the number is between 100 and 999
Group Thousands if the number is between 1000 and 999,999
Group Others if the number is greater than 999,999
My problem is I do not know where I should being placing them into my program (below)
import java.util.Scanner;
public class FourNumbersProgram {
private static int readNumber(String message, Scanner in) {
System.out.println("Enter a numbers divislbe by 4 or 6. No negatives.");
System.out.println("**If greater than 500: must be multiple of 10");
System.out.print(message);
while (!in.hasNextInt()) {
in.next();
System.out.println("Sorry, couldn't understand you!");
System.out.print(message);
}
int a = in.nextInt();
return a;
}
private static int readNumberToMatchCondition(String message, Scanner in) {
int number = 0;
do {
number = readNumber(message, in);
if (number < 500) {
if (number % 4 != 0 && number % 6 != 0) {
System.out.println(number + " not divisible by 4 or 6");
} else {
return number;
}
} else {
if (number % 4 != 0 && number % 6 != 0) {
System.out.println(number + " not divisible by 4 or 6");
} else if (number % 10 != 0) {
System.out.println(number + " is greater than 500 and not divisible by 10");
} else {
return number;
}
}
} while (true);
}
public static void main(String[] args) {
Scanner in = new Scanner(System.in);
int randomNumber1 = readNumberToMatchCondition("Enter first number:", in);
int randomNumber2 = readNumberToMatchCondition("Enter second number:", in);
int randomNumber3 = readNumberToMatchCondition("Enter third number:", in);
int randomNumber4 = readNumberToMatchCondition("Enter fourth number:", in);
int sum; // sum of number1, number2, number3, and number4
int avg; // average of number1, number2, number3, and number4
int largest; // largest number of the four integers
int smallest; // smallest number of the four integers
sum = (randomNumber1 + randomNumber2 + randomNumber3 + randomNumber4);
avg = ((sum) / 4);
smallest = randomNumber1;
smallest = (randomNumber2 < smallest) ? randomNumber2 : smallest;
smallest = (randomNumber3 < smallest) ? randomNumber3 : smallest;
smallest = (randomNumber4 < smallest) ? randomNumber3 : smallest;
largest = randomNumber1;
largest = (randomNumber2 > largest) ? randomNumber2 :largest;
largest = (randomNumber3 > largest) ? randomNumber3 :largest;
largest = (randomNumber4 > largest) ? randomNumber4 :largest;
System.out.println();
System.out.println("First number entered: " + randomNumber1); //prints first number entered
System.out.println("Second number entered: " + randomNumber2); //prints second number entered
System.out.println("Third number entered: " + randomNumber3); //prints third number entered
System.out.println("Fourth number entered: " + randomNumber4); //prints fourth number entered
System.out.println();
System.out.println("The sum is: " + sum); //prints sum of four numbers
System.out.println("The average is: " + avg); //prints average of four numbers
System.out.println("The smallest number is: " + smallest); //prints smallest of the four numbers
System.out.println("The largest number is: " + largest); //prints largest of the four numbers
System.out.println();
}
}
Here is a transcript of my code:
my professor gave me this sample of a grouping program (below)
import java.util.Scanner;
public class Prog2 {
public static void main(String[] args){
Scanner in = new Scanner(System.in);// read a number
System.out.println("Enter a number: ");
int number = in.nextInt();
if (number < 0) {
System.out.println("Error: Sorry, no negative numbers allowed.");
System.exit(0);
}
int grp1 = (number / 100) + 1;
int grp2 = (number / 1000) + 1;
int grp3 = (number / 1000000) + 1;
switch (grp1){
case 1: // Group Tens
System.out.println(number + " belongs to Group Tens");
break;
default:
switch (grp2) {
case 1:// Group Hundreds
System.out.println(number + " belongs to Group Hundreds");
break;
default:
switch (grp3) {
case 1:// Group Thousands
System.out.println(number + " belongs to Group Thousands");
break;
default:// Group Others
System.out.println(number + " belongs to Group Others");
}
}
}
in.close();
}
}
Heres a transcript of his code:
I know his program is asking for the user to type in one number and the program groups it. I was wondering how to put something like this into my program. I am confused because I have four numbers that have to be grouped and I'm not sure if I have to repeat something similar to my professors program for all of my four numbers (randomNumber1, randomNumber2, randomNumber3, randomNumber4
Please no positing an entire corrected code! I want to fix it myself and learn!
Your professors program will work for all of your numbers. All you need to do is call the method 4 times. Once for each number. What you need to do is put his code into a method on it's own. (Remember, if he's given it to you as a guide, then he will probably want you to give a go at writing the logic yourself).
Let's say you put his code in a method that looks like:
public void displayNumberGroup(int number)
{
// Displays number group using your prof's code.
}
Then, next, all you need to do is pass each value that you've loaded, into that method. For example: displayNumberGroup(randomNumber1);. This will calculate the grouping for that number. I'll leave it up to you to put this stuff into context, since you've requested to not be spoonfed the answer (which is very commendable!).
Instead of doing randomNumber1, randomNumber2, ect you can make them into an array. By doing that, you can then put a for loop over the given switch and run it 4 times so all of your numbers have groups. If you need me to explain any part of this with a simple example I will, but I know you want to do most of this yourself so if you have any questions let me know.
Related
I've got an assignment that requires me to use a loop in a program that asks the user to enter a series of integers, then displays the smallest and largest numbers AND gives an average. I'm able to write the code that allows the user to enter however many integers they like, then displays the smallest and largest number entered. What stumps me is calculating the average based on their input. Can anyone help? I'm sorry if my code is a little janky. This is my first CS course and I'm by no means an expert.
import javax.swing.JOptionPane;
import java.io.*;
public class LargestSmallest
{
public static void main(String[] args)
{
int number, largestNumber, smallestNumber, amountOfNumbers;
double sum, average;
String inputString;
inputString = JOptionPane.showInputDialog("Enter an integer, or enter -99 to stop.");
number = Integer.parseInt(inputString);
largestNumber = number;
smallestNumber = number;
sum = 0;
for (amountOfNumbers = 1; number != -99; amountOfNumbers++)
{
inputString = JOptionPane.showInputDialog("Enter an integer, or enter -99 to stop.");
number = Integer.parseInt(inputString);
if (number == -99)
break;
if (number > largestNumber)
largestNumber = number;
if (number < smallestNumber)
smallestNumber = number;
sum += number;
}
average = sum / amountOfNumbers;
JOptionPane.showMessageDialog(null, "The smallest number is: " + smallestNumber + ".");
JOptionPane.showMessageDialog(null, "The largest number is: " + largestNumber + ".");
JOptionPane.showMessageDialog(null, "The average off all numbers is: " + average + ".");
}
}
The problem is that you do an extra
inputString = JOptionPane.showInputDialog("Enter an integer, or enter -99 to stop.");
number = Integer.parseInt(inputString);
at the beginning. You don't count that in a sum. That's why you get unexpected results.
The fix would be:
replace the declarations line with:
int number = 0, largestNumber, smallestNumber, amountOfNumbers;
Remove
inputString = JOptionPane.showInputDialog("Enter an integer, or enter -99 to stop.");
number = Integer.parseInt(inputString);
That go before the loop
Replace for (amountOfNumbers = 0 with for (amountOfNumbers = 1
This is my first CS course
Then allow me to show you a different way to do your assignment.
Don't use JOptionPane to get input from the user. Use a Scanner instead.
Rather than use a for loop, use a do-while loop.
Usually you declare variables when you need to use them so no need to declare all the variables at the start of the method. However, be aware of variable scope.
(Notes after the code.)
import java.util.Scanner;
public class LargestSmallest {
public static void main(String[] args) {
Scanner stdin = new Scanner(System.in);
int largestNumber = Integer.MIN_VALUE;
int smallestNumber = Integer.MAX_VALUE;
int number;
double sum = 0;
int amountOfNumbers = 0;
do {
System.out.print("Enter an integer, or enter -99 to stop: ");
number = stdin.nextInt();
if (number == -99) {
break;
}
if (number > largestNumber) {
largestNumber = number;
}
if (number < smallestNumber) {
smallestNumber = number;
}
sum += number;
amountOfNumbers++;
} while (number != -99);
if (amountOfNumbers > 0) {
double average = sum / amountOfNumbers;
System.out.printf("The smallest number is: %d.%n", smallestNumber);
System.out.printf("The largest number is: %d.%n", largestNumber);
System.out.printf("The average of all numbers is: %.4f.%n", average);
}
}
}
largestNumber is initialized to the smallest possible number so that it will be assigned the first entered number which must be larger than largestNumber.
Similarly, smallestNumber is initialized to the largest possible number.
If the first value entered is -99 then amountOfNumbers is zero and dividing by zero throws ArithmeticException (but maybe you haven't learned about exceptions yet). Hence, after the do-while loop, there is a check to see whether at least one number (that isn't -99) was entered.
You don't need to use printf to display the results. I'm just showing you that option.
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Closed 2 years ago.
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So currently, I am working on a piece of code that will determine whether or not an integer is a prime number or not, and that works perfectly fine since I have tested it multiple times using different prime and non-prime integers. Now, I have to wrap it up by being able to list out all factors of any given integer and I just simply don't know what to do. Down below is my current program without the factors part that I need. I don't know where to start since I am not particularly good with "while loops" as we just learned about them today.
This is what I have to do, "The program should give the output of all factors of the integer using appropriate formatting so it the factors are clear.
It should output “The factors of (input) are:”
If the only factors of the integer input are 1 and itself, the program should state: “This is a prime number!” and if it is not
a prime number print nothing."
Any help with this would be greatly appreciated. Thanks!
import java.util.*;
public static void main(String[] args) {
Scanner console = new Scanner(System.in);
System.out.println("What is the number that you have chosen?");
int num = console.nextInt();
int div = 2;
boolean run = false;
System.out.println("The factors of " + num + " are:");
while (div <= Math.sqrt(num)) {
if (num % div == 0) {
System.out.println(div + " , " + num/div);
div++;
run = true;
} else {
div++;
}
}
if (run == false) {
System.out.print("This is a prime number!");
}
}
}
For starters, you can use this:
Scanner console = new Scanner(System.in);
int num = console.nextInt();
int factor = 1;
while(factor<=num) {
if(num%factor==0) {
System.out.println("Found factor: "+factor);
}
factor++;
}
console.close();
So what does it do?
What you want to do is loop through every single number from 1 all the way to the number. This is illustrated from the statement in the while loop while(factor<=num).
To check whether it is a factor, we can use the statement if(num%factor==0). What does this mean? % means modulus, and basically it returns the remainder after you divide a number by another number. If the remainder is 0, we know it is a factor (it can divide successfully. If you don't know what a factor is, I recommend you study mathematics first).
We then increment factor by 1 each time, and check every number smaller than the user input, since there is no use of checking larger numbers (a number is never a factor of another if it is larger).
Test Run
10
Found factor: 1
Found factor: 2
Found factor: 5
Found factor: 10
If you want to implement prime number verification, you can do:
Scanner console = new Scanner(System.in);
int num = console.nextInt();
int factor = 1;
int factors=0;
while(factor<=num) {
if(num%factor==0) {
System.out.println("Found factor: "+factor);
factors++;
}
factor++;
}
if(factors==2) {
System.out.println("This is a prime number!");
}
console.close();
FINAL VERSION (according to your requirements)
Scanner console = new Scanner(System.in);
int num = console.nextInt();
int factor = 1;
int factors=0;
System.out.print("The factors of "+num+" are: ");
while(factor<=num) {
if(num%factor==0) {
System.out.print(factor+" ");
factors++;
}
factor++;
}
if(factors==2) {
System.out.println("This is a prime number!");
}
console.close();
Test Case
2
The factors of 2 are: 1 2
This is a prime number!
boolean isPrime = true;
for(int i = 2; i <= num/2; i++){
if(num % i == 0) {
System.out.println("The factors of " + num + " are:" + i);
isPrime = false;
}
}
if(isPrime) {
System.out.print("This is a prime number!");
}
Something I want you to think is why I am running the loop only till num/2 and not till num? Let me know if you can figure it out.
Change your while loop a bit to store the factors.
List<Integer> factors = new Arraylist<>();
int upperLimit = num/2
while (div <= upperLimit) {
if (num % div == 0) {
factors.add(div);
}
}
If you do this at the end of the loop, the factors variable which is a list will have all the factors fo the numebr in it. Now you can check if there are numbers in the list other than 1 or itself and if so, its not a prime.
Note: Instead of a list you can also have an array if you are not aware if what lists are in java.
I just did small changes to your code. This will give the answer in the best time complexity possible.
import java.util.*;
public class myClass{
public static void main(String[] args) {
Scanner console = new Scanner(System.in);
System.out.println("What is the number that you have chosen?");
int num = console.nextInt();
int div = 2;
boolean run = false;
System.out.println("The factors of " + num + " are:");
System.out.print("1");
while (div <= Math.sqrt(num)) {
if (num % div == 0) {
System.out.print(" , "+div + " , " + num/div);
div++;
run = true;
} else {
div++;
}
}
System.out.print(" , "+num);
if (run == false) {
System.out.print("\nThis is a prime number!");
}
}
}
Test Cases
What is the number that you have chosen?
The factors of 10 are:
1 , 2 , 5 , 10
What is the number that you have chosen?
The factors of 5 are:
1 , 5
This is a prime number!
Hope this helps you out.
Write a program that reads integers, finds the largest of them, and counts its occurrences. Assume that the input ends with number 0. Suppose that you entered 3 5 2 5 5 5 0; the program finds that the largest is 5 and the occurrence count for 5 is 4.
Design the program such it allows the user to re-run the
program with a different inputs in the same run.
public void findLargestInteger(){
//create Scanner object
Scanner input = new Scanner(System.in);
int x;
do {
//prompt user input
System.out.print("Enter an integer, the input ends if it is 0:");
//declare variables
int n, countNeg = 0, countPos = 0;
float sum = 0;
//calculate how many positive and negative values, total, and average
while ((n = input.nextInt()) != 0) {
sum = sum + n;
if (n > 0) {
countPos++;
}
else if (n < 0) {
countNeg++;
}
}
//display results
if (countPos + countNeg == 0) {
System.out.println("No numbers are entered except 0");
System.exit(0);
}
System.out.println("The number of positives is " + countPos);
System.out.println("The number of negatives is " + countNeg);
System.out.println("The total is " + sum);
System.out.println("The average is " + (sum / (countPos + countNeg)));
}while ((x = input.nextInt()) != 0);
}
How can I get the prompt to display correctly at the end and keep it
running?
Output:
Enter an integer, the input ends if it is 0:
1 2 3 0
The number of positives is 3
The number of negatives is 0
The total is 6.0
The average is 2.0
1
Enter an integer, the input ends if it is 0:
1 2 3 0
The number of positives is 3
The number of negatives is 0
The total is 6.0
The average is 2.0
1
Enter an integer, the input ends if it is 0:
2 3 4 0
The number of positives is 3
The number of negatives is 0
The total is 9.0 The average is 3.0
1
Enter an integer, the input ends if it is 0:
2 3 4 0
The number of positives is 3
The number of negatives is 0
The total is 9.0
The average is 3.0
You could change while((x = input.nextInt()) != 0); to while(true); if you really want to keep repeating your program.
That IS an infinite loop though which is not really a good way to go.
So instead of looking for the next integer and compare with 0, maybe you should write something like
System.out.print("Do you want to quit? (y/n): ");
at the end of your loop (right before the while((x = input.nextInt()) != 0) line).
And then not check for 0 but for the y. At least then you don't have the program waiting for the user to input something without knowing what's happening.
Edit: Or you can just use a counter if you want to run it like twice or three times before it terminates ;)
Have you tried just calling your function inside a while loop?
public void findLargestInteger() {
// Your code
}
public static void main(String[] args) {
do {
findLargestInteger();
Scanner reader = new Scanner(System.in); // Reading from System.in
System.out.println("Would you like to continue? (0/1) ");
int n = reader.nextInt();
} while(n == 1);
}
This code seems to run well, but am getting error message regarding calculating the sum of the integers entered.
The point of the exercise is to input a series of numbers, and after the value -1 is entered, calculate the sum of the numbers, how many numbers were entered, the mean value, and the number of odd and even numbers.
The output I get suggests the program is running fine, but still get an eror message.
With input 1 17 2 18 17 -1 should print "sum: 55" expected:<55> but was: <0>
Apologies in advance if my Java syntax is a bit inelegant. I'm fairly new at this! Code below.
import java.util.Scanner;
public class LoopsEndingRemembering {
public static void main(String[] args) {
Scanner reader = new Scanner(System.in);
System.out.print("Type numbers: ");
int n;
double sum = 0.0;
int i = 0;
double average = 0.0;
int odd = 0;
int even = 0;
while (true) {
n = Integer.parseInt(reader.nextLine());
if (n != -1) {
System.out.print("Type numbers: ");
sum += n;
i++;
average = sum / i;
if (n % 2 == 0) {
even++;
} else {
odd++;
}
} else {
System.out.println("Thank you and see you later!");
System.out.println("The sum is " + sum);
System.out.println("How many numbers: " + i);
System.out.println("Average: " + average);
System.out.println("Even numbers: " + even);
System.out.println("Odd numbers: " + odd);
break;
}
}
}
}
You're printing 55.0. It seems you're getting this program tested by another program which you don't have access to the source code of.
Issue 1
You probably want to print 55 specifically.
Instead of:
double sum = 0.0;
Do:
int sum = 0;
Issue 2
Use int over double. Cast to double for the average value.
Then instead of this:
average = sum / i;
Do something like:
average = (double)sum / i;
Issue 3
Also, it seems the error message wants you to print as sum: 55.
So change this:
System.out.println("The sum is " + sum);
To:
System.out.println("sum: " + sum);
Beginner here. So I want to write a program that prints out all the prime numbers up to the number the user entered. E.g., user enters 5, program prints out 2 and 3. That part I understand, however what I am struggling with, is what if I want the program to print out whether the number the user entered is a prime or not (simple yes or no) IF the entered number is bigger than, let's say, 50. Here is code for first part:
public class Primes {
public static void main(String args[]) {
System.out.println("All primes up to: ");
int num = new Scanner(System.in).nextInt();
System.out.println("Prime numbers from 1 to " + num + " are: ");
for(int number = 2; number<=num; number++){
if(isPrime(number)){
System.out.println(number);
}
}
}
public static boolean isPrime(int number){
for(int i=2; i<number; i++){
if(number%i == 0){
return false;
}
}
return true;
}
}
I honestly can't wrap my around as to what I should be doing next. My first program ever ("Hello world" does not count ;P).
Edit :
Your current code seems to work fine.
As per your doubt as mentioned in one of the comments : Yes, but where do I add if statement that does the following: if the number entered is below 50, then the program prints out all the prime numbers up to the entered number. If the number the user entered is bigger than 50, it tells only whether the entered number is prime or not ( simply "It's a prime" or "No, it's not a prime"). Hope that made things clearer
The check you need to put is after you take the input :
int num = new Scanner(System.in).nextInt();
if( number > 50 )
{
if(isPrime(number))
{
// print out is prime
}
// print out it is not prime
}
else
{
System.out.println("Prime numbers from 1 to " + num + " are: ");
for(int number = 2; number<=num; number++){
if(isPrime(number)){
System.out.println(number);
}
}
}
SUGESTIONS :
However, just to touch upon the algorithmic part, I would recommend using Sieve of Eratosthenes for picking out all the prime numbers within a given range, as you need in your case.
Example :
To find all the prime numbers less than or equal to 30, proceed as follows:
First generate a list of integers from 2 to 30:
2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30
Strike (sift out) the multiples of 2 resulting in:
2 3 5 7 9 11 13 15 17 19 21 23 25 27 29
The first number in the list after 2 is 3; strike the multiples of 3 from the list to get:
2 3 5 7 11 13 17 19 23 25 29
The first number in the list after 3 is 5; strike the remaining multiples of 5 from the list:
2 3 5 7 11 13 17 19 23 29
The first number in the list after 5 is 7, but 7 squared is 49 which is greater than 30 so the process is finished. The final list consists of all the prime numbers less than or equal to 30.
Here's the code attached for reference ( Disclaimer : I'm picking up this code here from this site. Just pasted it here for more immediate visibility).
Code :
public class PrimeSieve {
public static void main(String[] args) {
int N = Integer.parseInt(args[0]);
// initially assume all integers are prime
boolean[] isPrime = new boolean[N + 1];
for (int i = 2; i <= N; i++) {
isPrime[i] = true;
}
// mark non-primes <= N using Sieve of Eratosthenes
for (int i = 2; i*i <= N; i++) {
// if i is prime, then mark multiples of i as nonprime
// suffices to consider mutiples i, i+1, ..., N/i
if (isPrime[i]) {
for (int j = i; i*j <= N; j++) {
isPrime[i*j] = false;
}
}
}
// count primes
int primes = 0;
for (int i = 2; i <= N; i++) {
if (isPrime[i]) primes++;
}
System.out.println("The number of primes <= " + N + " is " + primes);
}
}
Try this..
int j = 2; //variable
int result = 0; //variable
int number = 0; //variable
Scanner reader = new Scanner(System.in); //Scanner object
System.out.println("Please enter a number: "); //Instruction
number = reader.nextInt(); //Get the number entered
while (j <= number / 2) //start loop, during loop j will become each number between 2 and
{ //the entered number divided by 2
if (number % j == 0) //If their is no remainder from your number divided by j...
{
result = 1; //Then result is set to 1 as the number divides equally by another number, hergo
} //it is not a prime number
j++; //Increment j to the next number to test against the number you entered
}
if (result == 1) //check the result from the loop
{
System.out.println("Number: " + number + " is Not Prime."); //If result 1 then a prime
}
else
{
System.out.println("Number: " + number + " is Prime. "); //If result is not 1 it's not a prime
}
this is more efficient way tough:-
public boolean isPrime(int n) {
// fast even test.
if(n > 2 && (n & 1) == 0)
return false;
// only odd factors need to be tested up to n^0.5
for(int i = 3; i * i <= n; i += 2)
if (n % i == 0)
return false;
return true;
}
however what I am struggling with, is what if I want the program to print out whether the number the user entered is a prime or not (simple yes or no).
Your current isPrime function seems to work, so just ask for a number and test it.
Scanner scanner = new Scanner(System.in);
while (scanner.hasNextInt()) {
System.out.println("Enter a number (is it prime): ");
int num = scanner.nextInt();
if (isPrime(num)) {
System.out.printf("%d yes%n", num);
} else {
System.out.printf("%d no%n", num);
}
}
Or with a ternary,
Scanner scanner = new Scanner(System.in);
while (scanner.hasNextInt()) {
System.out.println("Enter a number (is it prime): ");
int num = scanner.nextInt();
System.out.printf("%d %s%n", num, isPrime(num) ? "yes" : "no");
}
Edit Based on your comment, move your print up sequence to a method
public static void primesUpTo(int num) {
System.out.println("Prime numbers from 1 to " + num + " are: ");
for (int number = 2; number <= num; number++) {
if (isPrime(number)) {
System.out.println(number);
}
}
}
Then
Scanner scanner = new Scanner(System.in);
while (scanner.hasNextInt()) {
System.out.println("Enter a number (is it prime): ");
int num = scanner.nextInt();
if (num > 50) {
System.out.printf("%d %s%n", num, isPrime(num) ? "yes" : "no");
} else {
primesUpTo(num); // <-- call the method above.
}
}
If i understand the question right:
If user enteres number lesser than or equal to 50, then print all primes that are lesser than that number.
Otherwise, just write if inputted number is a prime.
With already existing isPrime() method:
int num = new Scanner(System.in).nextInt();
if (num <= 50) {
System.out.println("Prime numbers from 1 to " + num + " are: ");
for (int number = 2; number <= num; number++) {
if (isPrime(number)) {
System.out.println(number);
}
}
} else { //num > 50
if(isPrime(num)) {
System.out.println(num + " is prime.");
} else {
System.out.println(num + " isn't prime.");
}
}