Develop Reference

How to randomise the characters '+' and '-' in java

I'm coding an arithmetic game where the user is asked a series of addition questions. I want to however randomly assign an operator for each question so that the question could be either:
Question 1: num1 + num2 =
or
Question 2: num1 - num2 =
I have been using the Math.random() method to randomise num1 and num2 the last thing I am struggling on is randomly generating '+' and '-'.
Is it something to do with the ASCII values of these two characters and then I can randomly pick between them? Thanks for the help!
As a side note, I want to ask the user to 'press enter' to start the game, but i'm not sure how to do it. Currently I've got the user to enter 'y' to start. Any ideas? Thanks so much.
//prompt user to start the game
System.out.println();
System.out.print("Press y to Start the Game: ");
String start_program = keyboard.next();
if (start_program.equals("y")) {
heres my code so far:
public static void main(String[] args) {
//mental arithmetic game
System.out.println("You will be presented with 8 addition questions.");
System.out.println("After the first question, your answer to the previous question will be used\nas the first number in the next addition question.");
//set up input scanner
Scanner keyboard = new Scanner(System.in);
//declare constant variables
final int min_range = 1, max_range = 10, Max_Number_of_Questions = 8;
long start_time, end_time;
//generate 2 random numbers
int random_number1 = (int) ((Math.random() * max_range) + min_range);
int random_number2 = (int) ((Math.random() * max_range) + min_range);
//declare variables
int question_number = 1;
int guess;
//prompt user to start the game
System.out.println();
System.out.print("Press y to Start the Game: ");
String start_program = keyboard.next();
if (start_program.equals("y")) {
//start timer
start_time = System.currentTimeMillis();
//ask the question
System.out.print("Question " + question_number + ": What is " + random_number1 + " + " + random_number2 + "? ");
//take in user input
guess = keyboard.nextInt();
while (guess == (random_number1 + random_number2) && question_number < Max_Number_of_Questions) {
System.out.println("Correct");
++question_number;
//generate a new question
//generate 2 random numbers
random_number1 = guess;
random_number2 = (int) ((Math.random() * max_range) + min_range);
//ask the question again
System.out.print("Question " + question_number + ": What is " + random_number1 + " + " + random_number2 + "? ");
//take in user input
guess = keyboard.nextInt();
}
end_time = System.currentTimeMillis();
int time_taken = (int) (end_time - start_time);
if (guess != (random_number1 + random_number2))
System.out.println("Wrong");
else {
System.out.println();
System.out.println("Well Done! You answered all questions successfully in " + (time_taken / 1000) + " seconds.");
}
}
}

You can use Random#nextInt to pick a random int from 0 to array.length - 1 which you can use as the index of an array of operators.
import java.util.Random;
public class Main {
public static void main(String[] args) {
char[] operators = { '+', '-', '*', '/' };
// Pick a random operator
Random random = new Random();
char op = operators[random.nextInt(operators.length)];
System.out.println(op);
}
}
A sample run:
/

I think for the random - and + characters you could use boolean like so:
Random rd = new Random(); // creating Random object
if(rd.nextBoolean()) {
//Do something
} else {
//Do Something else
}
For the enter, i think this is a game that is played in the console of the ide? Because then you can use a Scanner to track when enter is being pressed.
This will help you i think:
Java using scanner enter key pressed

The thing with the "Enter 'y' to start the game" is totally superfluous, as evidenced by the fact that you obviously don't have sensible things to do when the user does not enter 'y'.
So, since this is a command line application, why would anyone start it and then not want to play the game? Just go ahead and ask the first question! If the user did start that program by accident somehow, there will be no harm whatsoever, it's not that you're going to overwrite important files, start missiles or something like that.

You could try something like this.
Random r = new Random();
int[] signs = { 1, -1 };
char[] charSigns = { '+', '-' };
int a = r.nextInt(20);
int b = r.nextInt(20);
int sign = r.nextInt(2);
System.out.printf("%s %s %s = ?%n", a, charSigns[sign], b);
// then later.
System.out.printf("The answer is " + (a + signs[sign] * b));

How do i put the total sum of my input on top of my codes?

First of all here is my code
import java.util.Scanner;
public class Pengulangan {
public static void main(String[] args) {
Scanner sc = new Scanner (System.in);
int i, number, line, total;
int even, b = 0;
double rat;
System.out.print("Input number: ");
number = sc.nextInt();
even = number/2;
System.out.print("Total sum of number from 1 to number " + number + " is " + even + "\n");
i = 2;
line = 1;
while (i <= number) {
System.out.println("Even number-" + line + " is " +i);
line = line+1;
i = i +2;
}
total = ((number/2) * (even+1));
System.out.printf("Total sum of even number from the number " + number + " = " + total + "\n");
rat = 2*(total/number);
System.out.printf("Sum of average number from the number " + number + " = " + rat + "\n");
}
}
On this specific line on top of the second S.O.P
even = number/2;
i would like to put a loop there to find out how many Even numbers are on the input (ex- 10)
So i tried this code
int i = 1;
while (i <= number) {
if (i%2 == 0)
even = even + 1;
else
odd = odd + 1; //Not going to use this..
i++;
}
System.out.println("Total sum of even number is : ")
I tried putting that code in but i can't make it work, i tried it myself with only the code above and the results are exactly what im looking for but i can't put that in my first code ( the top one ), so i ended up using a sneaky way to get the even numbers.
I need help putting that total sum code to my main code

Sounds like a homework. You don't need loops or anything fancy, if you just want to get the sum of even numbers up to the number you input. Let n be the input number from your program and
class Main {
public static void main(String[] args) {
int n = 10;
//This is the math forumla
int total_sum_math = (((n/2)*((n/2)+1)));
System.out.println("Total sum of even number is : "+total_sum_math+"");
}
}
Reference: https://math.stackexchange.com/questions/3285727/sum-of-even-numbers-n

cannot find symbol error in condition of while loop

I'm writing a program for an assignment that should give random problems for the user to solve. what I am attempting to make it do is after selecting a problem type and answering one question the program should load the menu up again.
Originally I wrote a method that would be called in the else statement on line 147. The method successfully looped however the assignment specifically asks for a loop to make it happen. I've tried several different ways to change the loops condition statement but I'm not sure where I went wrong? any help would be appreciated.
I want very badly to use a switch statement but I can't as we haven't learned that in class.
// Importing Scanner and Random class for later.
import java.util.Scanner;
import java.util.Random;
class AlgebraTutor {
// Solve for Y method.
public static void solve_for_y() {
// Creation of a random number generator.
Random number_gen = new Random();
// Generates random integers from -100 to 100.
int var_m = number_gen.nextInt(101) - 100;
int var_x = number_gen.nextInt(101) - 100;
int var_b = number_gen.nextInt(101) - 100;
// Print problem out for student to see
System.out.println("Problem: y = " + var_m + "(" + var_x +")" + "+" + var_b);
System.out.println(" m =" + var_m);
System.out.println(" x =" + var_x);
System.out.println(" b =" + var_b);
// This formula will calculate the value of y.
float var_y = (var_m * var_x) + var_b;
// Using the scanners class a scanner object called userInput was created to record students answer. Answer was taken as a string and converted to an integer.
Scanner user_input = new Scanner(System.in);
System.out.println("Please solve for y:");
String user_answer = user_input.nextLine();
int answer = Integer.parseInt(user_answer);
if (answer == var_y){
System.out.println("correct");
}else{
System.out.println("incorrect, The answer is:" + var_y);
}
}
// -------------------------------------------------------------------------
// Solve for M method.
public static void solve_for_m() {
// Creation of a random number generator.
Random number_gen = new Random();
// Generates random integers from -100 to 100.
int var_y = number_gen.nextInt(101) - 100;
int var_x = number_gen.nextInt(101) - 100;
int var_b = number_gen.nextInt(101) - 100;
// Print problem out for student to see.
System.out.println("Problem: " + var_y + " = m (" + var_x +") + " + var_b);
System.out.println(" y =" + var_y);
System.out.println(" x =" + var_x);
System.out.println(" b =" + var_b);
// This formula will calculate the value of m.
float var_m = (var_y - var_b) / var_x;
// Using the scanners class a scanner object called userInput was created to record students answer. Answer was taken as a string and converted to an integer.
Scanner user_input = new Scanner(System.in);
System.out.println("Please solve for m:");
String user_answer = user_input.nextLine();
int answer = Integer.parseInt(user_answer);
if (answer == var_m){
System.out.println("correct");
}else{
System.out.println("incorrect, The answer is:" + var_m);
}
}
// -------------------------------------------------------------------------
// Solve for B method
public static void solve_for_b() {
// Creation of a random number generator.
Random number_gen = new Random();
// Generates random integers from -100 to 100.
int var_y = number_gen.nextInt(101) - 100;
int var_x = number_gen.nextInt(101) - 100;
int var_m = number_gen.nextInt(101) - 100;
// Print problem out for student to see.
System.out.println("Problem: " + var_y + " = " + var_m + " (" + var_x +") " + "+ b");
System.out.println(" y =" + var_y);
System.out.println(" x =" + var_x);
System.out.println(" m =" + var_m);
// This formula will calculate the value of m.
float var_b = var_y / (var_m * var_x);
// Using the scanners class a scanner object called userInput was created to record students answer. Answer was taken as a string and converted to an integer.
Scanner user_input = new Scanner(System.in);
System.out.println("Please solve for b:");
String user_answer = user_input.nextLine();
int answer = Integer.parseInt(user_answer);
if (answer == var_b){
System.out.println("correct");
}else{
System.out.println("incorrect, The answer is:" + var_b);
}
}
// -------------------------------------------------------------------------
public static void main(String[] args) {
do{
System.out.println("Which type of problem would you like to practice?");
System.out.println("1) Solve for y");
System.out.println("2) Solve for m");
System.out.println("3) Solve for b");
System.out.println("4) To quit");
Scanner selection_input = new Scanner(System.in);
String user_selection = selection_input.nextLine();
if ( user_selection.equals("1")){
solve_for_y();
} else if (user_selection.equals("2")){
solve_for_m();
} else if (user_selection.equals("3")){
solve_for_b();
} else if (user_selection.equals("4")){
System.out.println("Quitting Program");
System. exit(0);
} else{
System.out.println("Please choose from the given options");
}
} while(user_selection.equals("1") &&
user_selection.equals("2") &&
user_selection.equals("3") &&
user_selection.equals("4"));
}
}

You must declare the user_inpout variable outside the do...while loop, then you can check its value in the while() expression. Also you should initialize the scanner only once at the beginning of your program.
public static void main(String[] args)
{
Scanner selection_input = new Scanner(System.in);
String user_selection=null;
do
{
System.out.println("Which type of problem would you like to practice?");
System.out.println("1) Solve for y");
System.out.println("2) Solve for m");
System.out.println("3) Solve for b");
System.out.println("4) To quit");
user_selection = selection_input.nextLine();
if (user_selection.equals("1"))
{
solve_for_y();
}
else if (user_selection.equals("2"))
{
solve_for_m();
}
else if (user_selection.equals("3"))
{
solve_for_b();
}
else if (user_selection.equals("4"))
{
System.out.println("Quitting Program");
System.exit(0);
}
else
{
System.out.println("Please choose from the given options");
}
}
while (!user_selection.equals("4"));
}
For the case "4" you have two exists now:
else if (user_selection.equals("4"))
{
System.out.println("Quitting Program");
System.exit(0);
}
and:
while (!user_selection.equals("4"));
Only one of both is needed. So you may either remove the first one or replace the while statement by while(true).

Java Powers display table

I need to display an output like this:
Enter an integer: 3
Number Squared Cubed
====== ======= =====
1 1 1
2 4 8
3 9 27
But instead, when I run the code, I get this output:
Number Squared Cubed
====== ======= =====
3 9 27
In other words, I need to display the powers of an integer,including the powers of the numbers less than or equal to the integer. The numbers of the lesser integers need to be listed but are not displayed along with the integer being entered. How do I fix the code to make sure it outputs all of the integers that are less than or equal to the integer being entered? There are no errors (i.e. red exclamation mark circles) but I need to figure out the proper calculation.
Here is the code:
====================
import java.util.Scanner;
public class Powers
{
public static void main(String[] args)
{
System.out.println("Welcome to the Squares and Cubes Table");
System.out.println();
Scanner sc = new Scanner(System.in);
String choice = "y";
while(choice.equalsIgnoreCase("y"))
{
// get the input from the user
System.out.println("Enter an Integer: ");
int integerNext = sc.nextInt();
System.out.println("Number" + " " + "Squared" + " " + "Cubed");
System.out.println("======" + " " + "======" + " " + "======");
for(int i = 1; i <= integerNext; i++)
{
i = integerNext;
int numberSquared = (int) Math.pow(i, 2);
int numberCubed = (int) Math.pow (i, 3);
String message = "\n" + i + " " + numberSquared + " " + numberCubed;
System.out.println(message);
System.out.println();
// see if the user wants to continue
System.out.print("Continue? (y/n): ");
choice = sc.next();
System.out.println();
}
}
}
}
Help is always appreciated. Thanks.

Firstly, as Nikhil said: "Remove the line i = integerNext; It is resetting the value of I and therefore only last row is printed".
Secondly, move the first closing curly brace to before getting user input - you want to run the loop, and only ask about continuing when that's finished, if I understand correctly.

Remove the line i = integerNext; It is resetting the value of I and therefore only last row is printed

Your are almost there. Since you are looping from 1 to integerNext (which is 3 in your text), the looping variable i will get the values [1,2,3] each iteration, so you don't have to set i manually. When you do:
i = integerNext;
you are setting i to 3, so the loop will finish when it reaches the loop condition.
You may also want to put the "Continue?" check outside the loop:
for (int i = 1; i <= integerNext; i++) {
int numberSquared = (int) Math.pow(i, 2);
int numberCubed = (int) Math.pow(i, 3);
String message = "\n" + i + " " + numberSquared + " " + numberCubed;
System.out.print(message);
}
// see if the user wants to continue
System.out.print("\nContinue? (y/n): ");
choice = sc.next();
System.out.println();

import java.util.Scanner;
public class SquaresAndCubes {
public static void main(String[] args)
{
// Welcome the user
System.out.println("Welcome to the Squares and Cubes table");
System.out.println();
Scanner sc = new Scanner(System.in);
String choice = "y";
do
{
// Get input from the user
System.out.print("Enter an integer: ");
int integer = sc.nextInt();
// Create a header
String header = "Number " + "Squared " + "Cubed " + "\n"
+ "====== " + "======= " + "===== ";
System.out.println(header);
int square = 0;
int cube = 0;
String row = "";
for (int i = 1; i <= integer; i++)
{
square = i * i;
cube = i * i * i;
row = i + " " + square + " " + cube;
System.out.println(row);
}
// See if the user wants to continue
System.out.print("Continue? (y/n): ");
choice = sc.next();
System.out.println();
}
while (!choice.equalsIgnoreCase("n"));
}
}

Basic way to do it with foor loop and some printlines
Scanner sc = new Scanner(System.in);
System.out.print("What number would you like to go up to? ");
int userInt = sc.nextInt();
System.out.println("");
System.out.println("Here is your table!");
System.out.println("");
System.out.println("number | squared | cubed");
System.out.println("------ | ------- | -----");
for (int i = 1; i <= userInt; i++){
System.out.println(i + " | " + (i * i) + " |" + " " +(i * i * i));
}

Need help for my raffle program in java netbeans

I'm new to java programming and currently making this raffle program. Here is the sample output of the program.
Welcome to raffle 2013!
The Prize is <10 million - 100 million> //this is random. I already made.
Ticket number: <Generating unique 10 digits numbers>
//these are the required information for the user.
Name:
Address:
Contact:
Birthday:
//The final output
The winner of <PRIZE> is <NAME>, Ticket number.
I already have written some source code and I think I'm almost there. Unfortunately, I encountered a problem with the ticket number. The ticket number must generate 5 times with 10 digits number. The output must show the winner name together with his/her ticket number but the ticket number wasn't show and state that it is null. Here are the syntax I already made.
public class raffle2013 {
//Title: Raffle 2013
public static final int SIZE = 5;
public static final int SIZE1 = 5;
private static short x;
private static String randomNumber;
public static void main(String[] args) {
String[] names;
names = new String[SIZE];
String[] winner;
winner = new String[SIZE1];
System.out.println("Welcome To Raffle 2013");
long Low = 10000000;
long High = 100000000;
long randomPrize = (long) (Math.random() * High - Low) + Low;
System.out.println("The Prize is " + " " + randomPrize);
for (int a = 0; a < winner.length; a++) {
long randomNumber = (long) (Math.random() * 9000000000L);
System.out.println("Ticket number: " + randomNumber);
Scanner scan = new Scanner(System.in);
System.out.print("Name " + ":");
winner[a] = scan.nextLine();
Scanner scan2 = new Scanner(System.in);
System.out.print("Address" + ":");
names[x] = scan.nextLine();
Scanner scan3 = new Scanner(System.in);
System.out.print("Contact" + ":");
names[x] = scan.nextLine();
Scanner scan4 = new Scanner(System.in);
System.out.print("Birthday" + ":");
names[x] = scan.nextLine();
System.out.println(" ");
}
Random random = new Random();
int w = random.nextInt(SIZE1);
System.out.println("The winner of" + " " + randomPrize + " " + "Million Peso(s)" + "is" + " " + winner[w] + "," + " " + "Ticket Number:" + " " + randomNumber);
}
}
Note: the program can generate 10 digits unique numbers for the ticket number and generate it 5 times together with the names, however I have a problem of choosing the ticket number winner.
Here is the output in java netbeans:
run:
Welcome To Raffle 2013
The Prize is 38375493
Ticket number: 1991318978
Name :a
Address:a
Contact:a
Birthday:a
Ticket number: 194313423
Name :b
Address:b
Contact:b
Birthday:b
Ticket number: 6017170047
Name :c
Address:c
Contact:c
Birthday:c
Ticket number: 274411236
Name :d
Address:d
Contact:d
Birthday:d
Ticket number: 6183250376
Name :e
Address:e
Contact:e
Birthday:e
The winner of 38375493 Million Peso(s)is a, Ticket Number: null<--- bug
BUILD SUCCESSFUL (total time: 18 seconds)
the last output must show the winner name together with his/her ticket number. I hope you could help me. Please :)

Actually you have created randomNumber of String type outside the loop , while inside you have created randomNumber of type long...this long type is only accessible within the loop and the randomNumber you are calling is the one which is string type and it is null because you havent assigned any value to it..
What you have to do is to have an array of the randomNumber and save the ticket numbers as well and in the last as you are getting the winner[w] the same way you get randomNumber[w]

Looks like you're running into an issue with scope. You may also be slightly confused about data types, but let's see...
randomNumber is assigned as a long inside of your loop, but it is declared as a static String inside your class. The declaration inside of the loop is not applicable when coming to a wider scope (that is, inside of your main method), so you won't get any pertinent values from randomNumber.
That's weird in and of itself - the different data types don't make sense to me. You also don't need the static declaration of randomNumber either - it's only ever used in main, so you could just declare it there.
To get around that, you have to wrap the output from your random input instead, and drop the declaration:
randomNumber = Long.toString(Double.valueOf(Math.random() * 9000000000L).longValue());
Also, as a code smell, you've got too many Scanner instances; you should only really need one. I leave that as an exercise to the reader to clean up and refactor.

Similar to storing the winner, the ticket number has to be stored as well, and recalled when the output is printed
import java.util.Random;
import java.util.Scanner;
public class raffle2013 {
// Title: Raffle 2013
public static final int SIZE = 5;
public static final int SIZE1 = 5;
private static short x;
private static String randomNumber;
public static void main(String[] args) {
String[] names;
names = new String[SIZE];
String[] winner;
winner = new String[SIZE1];
long[] ticketNumber = new long[SIZE1];
System.out.println("Welcome To Raffle 2013");
long Low = 10000000;
long High = 100000000;
long randomPrize = (long) (Math.random() * High - Low) + Low;
System.out.println("The Prize is " + " " + randomPrize);
for (int a = 0; a < winner.length; a++) {
long randomNumber = (long) (Math.random() * 9000000000L);
System.out.println("Ticket number: " + randomNumber);
Scanner scan = new Scanner(System.in);
System.out.print("Name " + ":");
winner[a] = scan.nextLine();
ticketNumber[a] = randomNumber;
Scanner scan2 = new Scanner(System.in);
System.out.print("Address" + ":");
names[x] = scan.nextLine();
Scanner scan3 = new Scanner(System.in);
System.out.print("Contact" + ":");
names[x] = scan.nextLine();
Scanner scan4 = new Scanner(System.in);
System.out.print("Birthday" + ":");
names[x] = scan.nextLine();
System.out.println(" ");
}
Random random = new Random();
int w = random.nextInt(SIZE1);
System.out.println("The winner of" + " " + randomPrize + " "
+ "Million Peso(s)" + "is" + " " + winner[w] + "," + " "
+ "Ticket Number:" + " " + Long.toString(ticketNumber[w]));
}
}