Develop Reference

Infinite multiplication questions

I am trying to make a program that randomly generates two single digit numbers, creates a multiplication question, asks the user for the answer, counts the amount of questions and correct answers, and after every question the user is able to stop the loop to see how many he got correct out of the number of questions that were given.
I believe that I should be using a while loop (probably the easiest way) but I don't know exactly how to go about doing that. Here is what I currently have:
int number = 0;
int number1 = (int)(Math.random() * 10); //Produce two single digit numbers
int number2 = (int)(Math.random() * 10);
Scanner input = new Scanner(System.in); //Create Scanner
System.out.print("What is " + number1 + " + " + number2 + "? ");
int answer = input.nextInt();
while (number <= 10) {
if (number1 + number2 != answer ) {
System.out.println(" Incorrect!\n Would you like to see your overall result? (yes or no)");
}
else {
System.out.println(" Correct, great job!\n Would you like to see your overall result? (yes or no)");
}
}

Since this seems like an assignment I'll just give you pseudocode
MainMethod
{
//Create a new Random to generate random numbers
//(Import java.util.random)
//You need variables for:
//Total number of questions asked
//Total number of correct answers
//Start the question loop
while(true){
//Generate your two random numbers
//Ask the question
//Index the total number of questions
//Get their answer
//Check their answer
if(answer is correct){
//Index correct answers
}
//Ask whether they want to continue
//Check whether they want to stop
if(they want to quit){
//Break out of the while loop (break;)
}
}
//Tell them how many they got correct out of the total
}
Maybe I gave a little too much, but I hope this helps.

How can I input an if statement inside a while loop?

import java.util.Scanner;
public class ex11
{
static Scanner type=new Scanner(System.in);
public static void main(String args[])
{
int fact=1;
System.out.println("Enter a natural number ");
int num=type.nextInt();
int i=1;
while(i<=num)
{
fact*=i;
i++;
}
System.out.println("Factorial of number " + num + " is " + fact);
}
}
I'm trying to place a conditional statement inside the while loop. The condition is to test for would be that of, if num is a negative number, S.O.P.("You entered a negative #"); in other words,
if(num<0)
S.O.P.("You entered a negative #");
However it doesn't print it properly.

If you check inside the loop then it will not work it will still multiply the fact. You need to make sure that the num is not negative before you start the while loop.
int num = 0;
do {
if (num<0){
System.out.println("You printed out a negative number");
}
System.out.println("Enter a natural number ");
int num=type.nextInt();
} while (num<0);
Also on a side note you should probably close your scanners when you are done using them.

The question is hard to understand but from what i read it appears you want a loop to run until a value is entered that meets your pre-condition of being positive
System.out.println("Enter a non negative number :: ");
int num = type.nextInt();
while(num < 0){
System.out.println("The number you entered was negative!");
System.out.println("Enter a non negative number :: ");
num = type.nextInt();
}
Loops like this are crucial to making sure the data that you are using is within the pre-condition of your operation which could cause DivideByZero errors or other problems. This loop should be placed before you ever use the value of num so you can make sure it is within context of your program.

The problem is that if the num is negative, it won't go inside the while loop that is because before the while loop you have initialize i=1, since any negative number is lesser than 1 the condition for while loop become false. If you want to check whether num is negative insert the if condition before the while loop as follows
import java.util.Scanner;
public class ex11
{
static Scanner type=new Scanner(System.in);
public static void main(String args[])
{
int fact=1;
System.out.println("Enter a natural number ");
int num=type.nextInt();
int i=1;
if(num < 0) {
System.out.println("You entered a negative #");
}
else{
while(i<=num)
{
fact*=i;
i++;
}
System.out.println("Factorial of number " + num + " is " + fact);
}
}
}

To answer your question .... like this:
int i = 1; // HERE
while (i <= num) {
if (num < 0) {
System.out.println("You entered a negative #");
}
fact *= i;
i++;
}
However that is not going to work.
Suppose that "num" that you read is less than zero.
At the statement labeled "HERE", we set "i" to one.
In the next statement, we test "i < num".
Since "num" is less than zero, that test gives "false" and we skip over the entire loop!
That means that your conditional statement in the loop body would not be executed ... if "num" is less than zero.
Since this is obviously homework, I will leave it to you to figure out what you should be doing here. But (HINT!) it is not putting the conditional inside the loop.
(Please note: I have corrected a number of style errors in your code. Compare your original version with mine. This is how you should write Java code.)

You basically have to check whether the number is less than 0. This is to be done while taking the input. You can just take the input inside a while loop in this manner:
System.out.println("Enter a natural #");
while(true){ //loop runs until broken
num = type.nextInt();
if(num>=0)
break;
System.out.println("Wrong input. Please enter a positive number");
}
The program control breaks out of the loop if num>=0, i.e., positive, else, it continues to the next part of the loop and displays the error message and takes the input again.
Please note that natural numbers are the ones >= 1. In your program, you are actually trying to input a whole number which is >= 0.

How to input a lot of data until you type in an invalid number in java

User inputs numbers one by one and then once they type in an invalid number (has to be from 1-200) the program calculates the average of the numbers that were inputted.
I'm just wondering what would the code be for this. I know the one for inputting one piece of data. Example would be:
`Scanner in = new Scanner(System.in);
String numberOfShoes = "";
System.out.println("Enter the number of shoes you want: (0-200) ");
numberOfShoes = in.nextLine();`
this is just an example, but this time I want the user to input a lot of numbers. I know I'm going to include a loop somewhere in this and I have to stop it once it contains an invalid number (using a try catch block).
* I would also like to add that once the user inputs another number it always goes to the next line.

Just use a while loop to continue taking input until a condition is met. Also keep variables to track the sum, and the total number of inputs.
I would also suggest having numberOfShoes be an int and use the nextInt() method on your Scanner (so you don't have to convert from String to int).
System.out.println("Enter your number of shoes: ");
Scanner in = new Scanner(System.in);
int numberOfShoes = 0;
int sum = 0;
int numberOfInputs = 0;
do {
numberOfShoes = in.nextInt();
if (numberOfShoes >= 1 && numberOfShoes <= 200) { // if valid input
sum += numberOfShoes;
numberOfInputs++;
}
} while (numberOfShoes >= 1 && numberOfShoes <= 200); // continue while valid
double average = (double)sum / numberOfInputs;
System.out.println("Average: " + average);
Sample:
Enter your number of shoes:
5
3
7
2
0
Average: 4.25
It added 5 + 3 + 7 + 2 to get the sum of 17. Then it divided 17 by the numberOfInputs, which is 4 to get 4.25

you are almost there.
Logic is like this,
Define array
Begin Loop
Accept the number
check if its invalid number [it is how u define a invalid number]
if invalid, Exit Loop
else put it in the array
End Loop
Add all numbers in your array

I think you need to do something like this (which #Takendarkk suggested):
import java.util.Scanner;
public class shoes {
public void main(String[] args){
int input = 0;
do{
Scanner in = new Scanner(System.in);
String numberOfShoes = "";
System.out.println("Enter the number of shoes you want: (0-200) ");
numberOfShoes = in.nextLine();
input = Integer.parseInt(numberOfShoes);
}while((input>=0) && (input<=200));
}
}

you can use for loop like this
for(::)
{
//do your input and processing here
if(terminating condition satisified)
{
break;
}
}

Checking for negative values with scanner in

I have just written my first java program for a class I am taking which is used to give a student graduation information based on the credits for each class remaining. I have gotten everything to work except the required entry to check for negative values. Please see below and let me know if you have any ideas. Thanks in advance.
package txp1;
import java.util.ArrayList;
import java.util.Scanner;
public class txp1 {
public static void main(String[] args) {
// TODO code application logic here
System.out.println("Welcome to the University Graduation Calculator!");
System.out.println();
System.out.println("This calculator will help determine how many terms "
+ "you have remaining and your tuition total based upon credits"
+ " completed per semester.");
System.out.println();
double tuitionpersem = 2890;
System.out.println("We will begin by entering the number of credits for"
+ " each class remaining toward your degree.");
double sum = 0;
ArrayList<Double> credit = new ArrayList<>();
{
System.out.println("Please enter the number of credits for each individual class on a separate line and then press enter, Q to quit:");
Scanner in = new Scanner(System.in);
double number = 0;
number = Integer.parseInt(in.nextLine());
if (number <= 0);
{
System.out.println("The number of credits must be greater than zero!");
}
while (in.hasNextDouble()) {
credit.add(in.nextDouble());
}
for (int i = 0; i < credit.size(); i++) {
sum += credit.get(i);
}
System.out.println("Total credits remaining: " + sum);
}
int perterm = 0;
System.out.println("How many credits do you plan to take per term? ");
Scanner in = new Scanner(System.in);
perterm = Integer.parseInt(in.nextLine());
if (perterm <= 0);
{
System.out.println("The number of credits must be greater than zero!");
}
double totterms = sum / perterm;
totterms = Math.ceil(totterms);
System.out.print("Your remaining terms: ");
System.out.println(totterms);
double terms = (totterms);
System.out.print("The number of months to complete at this rate is: ");
System.out.println(6 * terms);
double cost = terms * 2890;
System.out.println("The cost to complete at this rate is: " + cost);
}
}

double number = 0;
number = Integer.parseInt(in.nextLine());
if (number <= 0);
The ";" at the end of if statement is the end of it. You are not doing anything with the result of number <=0. I believe you meant it to be like:
if (number <= 0){
//operations….
}
Notice that you create number of type double, then assign an int (parsed from String) to it. You can use nextDouble method to get a double directly, and if you plan this number to be an Integer anyway then use type int instead of double and nextInt instead of parsing. For more information about parsing from input, check Scanner documentation.

Your if statements terminate if you put a semi colon at the end of them. Effectively ending your logic right there. The program basically checks the condition and then moves on. Which in turn executes your second statement regardless of what number <= 0 resolves to.
//Does not get expected results
if (number <= 0);
{
//Gets executed regardless of condition
System.out.println("The number of credits must be greater than zero!");
}
//Gets expected results
if (number <= 0)
{
//Gets executed only if the condition returns true
System.out.println("The number of credits must be greater than zero!");
}
Edit: Changed due to some helpful input.
2nd Edit: I would also consider putting a loop in your code that makes the user re-enter input to get the desired value. If you put in a negative value your code will just spit the error message and keep running which can make you scratch your head. Unless your teacher isn't grading on that then forget all of what I just said. =p

Finding the Average from a list of numbers in Java

This is my first attempt at java problem I have been given as part of my Programming assignment.
I must make a program which calculates the average of a list of numbers that a user enters. the data enty should be terminated when 0 is entered. my problem is with this "ALL NEGATIVE NUMBERS SHOULD BE IGNORED"
for some reason the following code does not work, when I enter a negative number it should be ignored but for some reason it terminates the data enty
import java.util.*;
class Task_8
{
public static void main()
{
Scanner inputLine = new Scanner(System.in);
float row, numberentered, numbersum = 0, negativenumber = 0;
double result, count = 0;
System.out.println ("Welcome to Task 8 of 10 of my Programming Assignment... Nearly There!");
System.out.println ("_____________________________________________________________________");
System.out.println ();
System.out.println ("Enter as many numbers as you like and this program will tell you the arithmatic mean");
System.out.println ("Terminate data entry by entering 0");
do{
System.out.print ("Please enter a number: ");
numberentered = inputLine.nextInt();
count++;
if (numberentered < 0)
{
numberentered = negativenumber;
}
numbersum = ( numberentered + numbersum ) - negativenumber;
}
while ( numberentered !=0 );
result = numbersum/count;
System.out.println ();
System.out.println ("*************************************");
System.out.println ();
System.out.println ("The sum of all of the numbers you entered is " +numbersum);
System.out.println ("You entered " + count + " numbers");
System.out.println ("The Average/mean of the numbers that you entered is " + result);
System.out.println ();
System.out.println ("*************************************");
}
}
any Ideas guys?
Thank you

The variable negativenumber always has the value zero. When you set numberentered to negativenumber the "while" condition is met, and the loop exits. A better strategy would be to us "continue" to skip the rest of the loop body when a negative number was entered.

If you want to ignore the negative number, then don't include it in your calculation. Instead do something like:
if (numberentered > 0)
{
numbersum += numberentered;
}

Examine the following block of code:
if (numberentered < 0)
{
numberentered = negativenumber;
}
What this is doing is setting numberentered to 0. Then, at the end of your do-while loop, you have this:
while(numberentered != 0);
So, whenever the user types in a negative number, you set numberentered to zero. When you reach the end of the loop, numberentered != 0 is false, so the loop exits.
The simpler solution, and something more akin to what you will learn to do on a regular basis in the future, is to simply check the value of the number in an if statement and then add it or not based on its value.
if(numberentered > 0)
numbersum += numberentered;
This is clean, concise, and removes the need for the negativenumber variable which is superfluous and could be confusing. If you were looking at this code a year from now, would you remember what negativenumber meant, or why it was set to zero? Write your code as if somebody else will have to read it and understand it. Your professors will, and, in the future, your colleagues will.
On another note, you are reading in integers (with inputLine.nextInt()) but storing them in a float. You've also declared count as a double. You most likely will want to declare count, numberentered, and numbersum as an int.

You never assign a value other than 0 (in initialization) to negativenumber, then you do
if (numberentered < 0)
{
numberentered = negativenumber;
}
and the do...while-loop terminates because numberentered is 0.