Develop Reference

Count How many number multiple by the number from input user between a range

again I have a problem with doing practice prepare for the exam.
Would everyone help me? Thanks a lot
write a program input an integer in the range 100 to 200 inclusive. If the user enters invalid input then your algorithm should re-prompt the user until the input is valid. Your algorithm should then count how many numbers between 500 and 1000 which are multiples of the number input. Finally, the count should be output to the user. You should make good use of sub-modules.
Here my code
import java.util.*;
public class Exam3
{
public static void main(String args[])
{
int count = 0;
int input = 0;
Scanner sc = new Scanner(System.in);
System.out.println("Enter number: ");
input = sc.nextInt();
while(input < 100 || input > 200)
{
System.out.println("Enter number between 100 to 200");
input = sc.nextInt();
count ++;
}
System.out.println("count is: " + count);
}
public static void int getCount(int input, int count)
{
for(int i = 499;i <= 1000; i++ )
{
if(i % input==0)
{
count++;
}
}
return count;
}
}

The algorithm should be:
Having correct input, find all multiples of it that are in range [500, 1000]. Count them.
It's a bad approach to check all the numbers, as we know from our math knowledge, that between k*a and k*a + a there is no number divisible by a.
Knowing that and having input we enlarge our temp initialized with value of input by input. If it's in range [500, 1000] we enlarge our counter. Simple as that.
public static void main(String args[]) {
int count = 0;
int input = 0;
Scanner sc = new Scanner(System.in);
System.out.println("Enter number: ");
input = sc.nextInt();
while (input < 100 || input > 200) {
System.out.println("Enter number between 100 to 200");
input = sc.nextInt();
count++;
}
System.out.println(input + " fits " + count(input) + " times");
}
private static int count(int input) {
int result = 0;
int temp = input;
while (temp <= 1000) {
if (temp >= 500) {
result++;
}
temp += input;
}
return result;
}
According to your code, I see some issues. I'll point them out, as it is important for practicing Java.
Method can be either void or return int. You can't have void int. In this case, we return int, so int is the return type,
It's important to stick to Java styling. Don't put too many empty lines, keep indents.
Use Eclipse or IntelliJ (IntelliJ is more pro). They will point unused code blocks, so you would know that that getCount wasn't called.

Using a for loop, display the number of entries and the sum in Java

so I was asked to create a program in which the user enters four integers and then displays the number of entries and the sum of the integers using a for loop. This is what I came up with.
import java.util.Scanner;
public class Program
{
public static void main(String[] args)
{
Scanner in = new Scanner(System.in);
int sum = 0;
int count = 0;
for (int i = 0; i != 4 ; i++)
{
System.out.println(" Enter an integer: ");
int num = in.nextInt();
sum = sum + num;
count = count + 1;
}
System.out.println("Number of entries: " + count);
System.out.println("Total sum of entries: " + sum);
}
}
I was wondering what a cleaner way was to ask the user for the four numbers using a for loop, and what other people might suggest be best for this situation. Thanks for any input, p.s. (I have just started learning!)

i think you are looking something like this
public static void main(String[] args) {
Scanner sc = new Scanner(System.in);
int sum=0;
for(int i=0;i<4;i++){
System.out.println("ENter Number"+(i+1));
sum += sc.nextInt();
}
System.out.println("the Sum is "+sum);
sc.close();
}

You can check with enter. If user presses enter, you can break.
enterkey = readinput.nextLine();
System.out.print(enterkey);
if(enterkey.equals("")){
break;
}

Have a look at this solution. I cleaned it up a bit. Maybe you will find some design decisions I made which will help you in the future:
public static void main(String[] args) {
try (Scanner scanner = new Scanner(System.in)) {
int sum = 0;
for (int count = 1; count <= 4; count++) {
System.out.print(String.format("Please enter %d. integer: ", count));
sum = sum + readNumber(scanner);
}
System.out.println("The sum of numbers entered is: " + sum);
}
}
private static int readNumber(Scanner scanner) {
do {
String input = scanner.nextLine();
try {
return Integer.parseInt(input);
} catch (NumberFormatException e) {
System.out.print(String.format("Input %s is not a valid integer. Try again: ", input));
}
} while (true);
}

As you're a beginner it's the best way for getting input from the user in console. But you are for the condition should be like:
for ( int i =0;i < 4 ; i ++){}

How to find the average in a do-while loop

I have to write a program that asks the user to enter an integer value. After each value, the user has to respond with a "y" or a "n" if he/she wants to continue with the program, and each number the user enters is stated as either odd or even.
I have done this so far with a do-while loop, but I am confused on how to get the averages of the values the user enters. How would you get the average for all the numbers entered?
Here is my code so far:
import java.util.Scanner;
class ProgramTest {
public static void main(String[] args) {
String answer = "";
do {
int num, count = 0;
Scanner scan = new Scanner(System. in );
System.out.print("Enter any number : ");
num = scan.nextInt();
if ((num % 2) == 0) System.out.println(num + " is an even number.");
else System.out.println(num + " is an odd number");
System.out.println("do you want to continue?");
answer = scan.next();
count++;
} while (answer.equals("y"));
}
}

From the Question looks like following things need to handled,
haven't add mechanism for addition into single variable.
put all variable to out from do...while loop body...
created additional variable according to requirement.
see all this things covered by me with following code snippet.
do something likewise,
String answer = "";
double sum = 0; // use for storing addition to all entered values..
int num, count = 0;
Scanner scan = new Scanner(System.in);
do {
System.out.print("Enter any number : ");
num = scan.nextInt(); // getting input from user through console
sum = sum + num; // add every input number into sum-variable
if ((num % 2) == 0) System.out.println(num + " is an even number.");
else System.out.println(num + " is an odd number");
System.out.println("do you want to continue?");
answer = scan.next(); // ask for still want to repeat..
count++;
} while (answer.equals("y"));
System.out.println("Average is : " + sum + "/" + count + " = "+ (sum /count));

In order to calculate Average, you need 2 things: Sum of all numbers and Count of all numbers involved in the Average calculation.
Your sum and count which involved in the Average calculation needs to be out of the do..while scope in order for them to be known at the calculation stage.
I also took the liberty of fixing your code a little bit
import java.util.Scanner;
class ProgramTest {
public static void main(String[] args) {
Scanner scan = new Scanner(System. in );
int count = 0;
int sum = 0;
String answer = "";
do {
System.out.print("Enter any number : ");
int num = scan.nextInt();
boolean isEven = (num % 2 == 0);
System.out.println(num + " is an " + (isEven ? "even" : "odd") + " number.");
sum += num;
System.out.println("do you want to continue?");
answer = scan.next();
count++;
} while (answer.toLowerCase().equals("y"));
System.out.println("Average: " + (sum/count));
}
}

Change your code like this:
import java.util.Scanner;
class ProgramTest {
public static void main(String[] args) {
String answer = "";
int avr =0;
int num, count = 0;
do {
Scanner scan = new Scanner(System. in );
System.out.print("Enter any number : ");
num = scan.nextInt();
if ((num % 2) == 0) System.out.println(num + " is an even number.");
else System.out.println(num + " is an odd number");
System.out.println("do you want to continue?");
avr += num;
answer = scan.next();
count++;
} while (answer.equals("y"));
avr = avr /count;
System.out.println("The avreage of value is:" + avr );
}
}
avr is average. that means when you input an integer. we add num and avr . and when finish looping. we divideto count. like this:
1-5-9-11
avr = 1+5+9+11;
count = 4;
avr = avr/4;

Java scanner count numbers that are in an interval

I'm new with java and i have to write a code that asks the user two numbers an interval. Then the user must introduce n numbers and the program must return how many numbers belong to that interval.
I've tried to do this and this is what i have:
import java.util.*;
public class NumsInter {
public static void main(String[] args) {
Scanner sc;
int a,b,nums,count;
sc = new Scanner (System.in);
System.out.print ("Write two numbers a and b(a<=b)(interval): ");
a=sc.nextInt();
b=sc.nextInt();
count=0;
System.out.println("write a number: ");
while(sc.hasNextInt()){
nums=sc.nextInt();
if (a<=nums && nums>=b){
count= count + 1;
} else {
count= count;
}
}
System.out.println(count +" numbers are included in ("+a+","+b+")");
}
}
Example: If the user writes 2 and 6, and then 4,4,3,1 the output should be 3.
As I am a newbie i don't know how can i do this the good way, can someoen help?
PD: How can i break the loop so i can get the output?
Thank You!

Try something like this
ArrayList<Integer> numbers = new ArrayList<Integer>();
System.out.println("Enter the numbers you want to test, enter 'stop' to stop");
boolean userInput = true;
while(input.hasNextInt() && userInput){
if(input.hasNext("stop")){userInput = false;}
numbers.add(input.nextInt());
}
Where you have a loop that checks if there is a next int while at the same time checking to see if the user is done or not.
And them something like this to print your answer
for(int i =0; i < numbers.size(); i++){
testNum = numbers.get(i);
if(testNum > lowerLimit && testNum < upperLimit){
count++;
}
}
System.out.println(count + " valid numbers have been entered!");

take an int [] no_between_max&min after take the input from user and store in this array. after that take a for loop and compare the value of array with max and min ant increase the count variable.
int noOfItem=sc.nextInt();
int [] no_between_max_min = new int[noOfItem];
for(int i=0;i<noOfItem;i++){
no_between_max_min[i]=sc.nextInt();
}
for(int i=0;i<no_between_max_min.length;i++){
if(no_between_max_min[i]>=a&&no_between_max_min[i]<=b){
count++;
}
}

Average user inputted numbers in Java

I am trying to get the average of user inputted numbers. Every time I input numbers the output is always-
The sum is 6
How many numbers: 4
Average: 2.0
A while loop is required, unfortunately for loops are not allowed. I am pretty new to Java so my formatting is sloppy. Where in my code are my problems?
import java.util.Scanner;
public class LoopsEndingRemembering {
public static void main(String[] args) {
// program in this project exercises 36.1-36.5
// actually this is just one program that is split in many parts
Scanner reader = new Scanner(System.in);
int count = 0;
int sum = 0;
int endingVariable = -1;
int input = 0;
double average;
while (input >= endingVariable) {
System.out.println("Type numbers: ");
input = Integer.parseInt(reader.nextLine());
sum += count;
average = (double)sum / count;
count++;
if (input == endingVariable) {
System.out.println("Thank you and see you later!");
System.out.println("The sum is " + sum);
System.out.println("How many numbers: " + count);
System.out.println("Average: " + average);
break;
}
}
}
}

You have several errors here.
The main one that causes your error is sum += count. Instead of adding what the user has entered, you are adding the number that shows how many numbers there are. So it will always add 0+1+2+3 etc.
Another problem is that, once you change the above, you have to check whether the input == endingVariable before you add the input to the sum. So you have to write the if first, and then calculate the average inside it. Otherwise it will treat your -1 as part of the sequence of numbers to calculate.
You only need to add the input to the sum and increment the count if you find out that the input is not yet the same as endingVariable.
So:
Add the input, not the count, to the sum.
Calculate the average only when you have reached the final item.
Add the input to the sum and increment the counter only if your input is not endingVariable.

Try this one...
import java.util.Scanner;
public class LoopsEndingRemembering {
public static void main(String[] args) {
// program in this project exercises 36.1-36.5
// actually this is just one program that is split in many parts
Scanner reader = new Scanner(System.in);
int count = 0;
int sum = 0;
int endingVariable = -1;
int input = 0;
double average;
while (input >= endingVariable) {
System.out.println("Type numbers: ");
input = Integer.parseInt(reader.nextLine());
sum += input; // you were doing mistake here.
average = (double)sum / count;
count++;
if (input == endingVariable) {
System.out.println("Thank you and see you later!");
System.out.println("The sum is " + sum);
System.out.println("How many numbers: " + count);
System.out.println("Average: " + average);
break;
}
}
}
}

Two big issues with your code. First, this line:
sum += count;
It's probably just a typo, but it should be obviously:
sum += input;
Second, once you fix that, you will notice you are including the -1 in your sum. You probably want something like this:
System.out.println("Type numbers: ");
input = Integer.parseInt(reader.nextLine());
if (input == endingVariable) {
average = (double) sum / count;
System.out.println("Thank you and see you later!");
System.out.println("The sum is " + sum);
System.out.println("How many numbers: " + count);
System.out.println("Average: " + average);
break;
} else {
sum += input;
count++;
}

Thank you for explaining in detail. It works fine now, all I had to do was what you said is change the input, and move the sum += input and count after the final item in an else. I was having the hardest time trying to figure out why my -1 was being included