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Do-While Loop not looping - Java

I am having a problem with my java code below. I want the loop to stop when the number "-100" but it stops as soon as you enter any number. I'm just learning how to use java so there could be plenty of mistakes here.
public static void main(String[] args){
Scanner keyboard = new Scanner (System.in);
String num = "";
do {
System.out.println("Enter a number: ");
int n = keyboard.nextInt();
System.out.println("The number you entered is: " +n);
System.out.println("------------------------");
} while ("-100".equals(num));
}
}

num is always the empty string, because you never change the value of num. You update n. Which is what I would base the loop on. Like,
Scanner keyboard = new Scanner(System.in);
int n;
do {
System.out.println("Enter a number: ");
n = keyboard.nextInt();
System.out.println("The number you entered is: " + n);
System.out.println("------------------------");
} while (n != -100);
That is, do loop while n is not -100.

Reading multiple inputs from Scanner

(I'm a beginner at Java)
I am trying to write a program that asks for 6 digits from the user using a scanner, then from those 6 individual digits find the second highest number. So far this works however I'd like to have the input read from a single line rather than 6 separate lines. I've heard of delimiters and tokenisation, but have no idea how to implement it. I'ld like to have it read like "Enter 6 digits: 1 2 3 4 5 6" and parsing each digit as a separate variable so i can then place them in an array as shown. If anyone could give me a run-down of how this would work it would be much appreciated. Cheers for your time.
public static void main(String[] args)
{
//Ask user input
System.out.println("Enter 6 digits: ");
//New Scanner
Scanner input = new Scanner(System.in);
//Assign 6 variables for each digit
int num1 = input.nextInt();
int num2 = input.nextInt();
int num3 = input.nextInt();
int num4 = input.nextInt();
int num5 = input.nextInt();
int num6 = input.nextInt();
//unsorted array
int num[] = {num1, num2, num3, num4, num5, num6};
//Length
int n = num.length;
//Sort
Arrays.sort(num);
//After sorting
// Second highest number is at n-2 position
System.out.println("Second highest Number: "+num[n-2]);
}
}

Your solution does this allready!
If you go through the documentation of scaner you will find out that your code works with different inputs, as long they are integers separated by whitespace and/or line seperators.
But you can optimice your code, to let it look nicer:
public static void main6(String[] args) {
// Ask user input
System.out.println("Enter 6 digits: ");
// New Scanner
Scanner input = new Scanner(System.in);
// Assign 6 variables for each digit
int size=6;
int[] num=new int[size];
for (int i=0;i<size;i++) {
num[i]=input.nextInt();
}
Arrays.sort(num);
// After sorting
// Second highest number is at n-2 position
System.out.println("Second highest Number: " + num[size - 2]);
}
As an additional hint, i like to mention this code still produces lot of overhead you can avoid this by using:
public static void main7(String[] args) {
// Ask user input
System.out.println("Enter 6 digits: ");
// New Scanner
Scanner input = new Scanner(System.in);
// Assign 6 variables for each digit
int size=6;
int highest=Integer.MIN_VALUE;
int secondhighest=Integer.MIN_VALUE;
for (int i=0;i<size-1;i++) {
int value=input.nextInt();
if (value>highest) {
secondhighest=highest;
highest=value;
} else if (value>secondhighest) {
secondhighest=value;
}
}
//give out second highest
System.out.println("Second highest Number: " + secondhighest);
}
if you do not like to point on highest if there are multiple highest, you can replace the else if:
public static void main7(String[] args) {
// Ask user input
System.out.println("Enter 6 digits: ");
// New Scanner
Scanner input = new Scanner(System.in);
// Assign 6 variables for each digit
int size = 6;
int highest = Integer.MIN_VALUE;
int secondhighest = Integer.MIN_VALUE;
for (int i = 0; i < size - 1; i++) {
int value = input.nextInt();
if (value > highest) {
secondhighest = highest;
highest = value;
} else if (secondhighest==Integer.MIN_VALUE&&value!=highest) {
secondhighest=value;
}
}
// give out second highest
System.out.println("Second highest Number: " + secondhighest);
}

Of course, there are many ways to do that. I will give you two ways:
1. Use lambda functions - this way is more advanced but very practical:
Integer[] s = Arrays.stream(input.nextLine().split(" ")).map(Integer::parseInt).toArray(Integer[]::new);
first create a stream, you can read more about streams here
than read the whole line "1 2 3 ...."
split the line by space " " and after this point the stream will look like ["1", "2", "3" ....]
to convert the strings to int "map" operator is used
and finally collect the stream into Integer[]
You can use an iterator and loop as many times as you need and read from the console.
int num[] = new int[6];
for (int i = 0; i < 6; i++) {
num[i] = input.nextInt();
}

There are several ways to do that:
take a single line string, then parse it.
Scanner input = new Scanner(System.in);
....
String numString = input.nextLine();
String[] split = numString.split("\\s+");
int num[] = new int[split];
// assuming there will be always atleast 6 numbers.
for (int i = 0; i < split.length; i++) {
num[i] = Integer.parseInt(split[i]);
}
...
//Sort
Arrays.sort(num);
//After sorting
// Second highest number is at n-2 position
System.out.println("Second highest Number: "+num[n-2]);

Creating a run time array that takes user input and creates array at run time & accepts 3 variables to calculate sum and average

I keep getting the error "cannot find symbol 'arr' " How do I accept both the array as a user input (being a float not a double) and 3 float variables as elements in the array?
import java.util.Scanner;
public class runtime_array
{
public static void main(String[] args){
System.out.println("Program creates array size at run-time");
System.out.println("Program rounds sum and average of numbers to two decimal places");
System.out.println("Note: numbers *must* be float data type");
System.out.println(); //blank line
// taking String array input from user
Scanner input = new Scanner(System.in);
System.out.println("Please enter length of String array");
int length = input.nextInt();
arr[i] = input.nextInt();
// create an array to save user input
float[] input = new float[length];
float[] input = new float[arr];
// loop over array to save user input
System.out.println("Please enter array elements");
for (int i = 0; i < length; i++) {
}
float sum = 0;
System.out.println("The array input from user is : ");
for(int i = 0; i < arr.length; i++){
System.out.println(String.format("%.2f", Float.valueOf(arr[i])));
sum += Float.valueOf(arr[i]);
}
System.out.println("The sum is: " + String.format("%.2f",sum));
System.out.println("The average is: " + String.format("%.2f",(sum/length)));
}
}

You've got a couple issues here
First, you cannot declare float[] input because you've already given Scanner to the reference for input. You need to name your float[] something different. Let's go with userInput.
Scanner input = new Scanner(System.in);
System.out.println("Please enter length of String array");
int length = input.nextInt();
float[] userInput = new float[length];
Next, you are trying to do things with arr before you have declared it. However, I don't even think you need a reference to arr. You should remove this line.
arr[i] = input.nextInt();
Furthermore, you need to prompt your user during each loop iteration, as well as append the Scanner input to float[] userInput.
for (int i = 0; i < length; i++) {
System.out.println("Please enter array elements");
userInput[i] = input.nextInt();
}

Creating if statement for the small program [closed]

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I am currently struggling with my first java program.
The question's task was to create a program that prompts the user to enter 5 numbers and store them in an array. Then the array should be printed, after that's done the program prompts the user to enter a number to search. Depending on the number the program should print "(display number) is on the list" or "(display number) is not on the list"
I have been struggling with this for quite a while now not fully understanding the conditional task.
Here is what my code looks like:
public class NewClass {
public static void main(String[] args) {
java.util.Scanner input = new java.util.Scanner(System.in);
// Enter three numbers
System.out.print("Enter five numbers: ");
int number1 = input.nextInt();
int number2 = input.nextInt();
int number3 = input.nextInt();
int number4 = input.nextInt();
int number5 = input.nextInt();
System.out.println("The sorted numbers are "
+ number1 + ", " + number2 + ", " + number3 + ", " + number4 + ", " + number5);
System.out.println("Enter a number to search: ");
}

I added comments to document what the code was doing. This should hopefully help you grasp the concept.
public class NewClass {
public static void main(String[] args) {
Scanner input = new Scanner(System. in );
//Create an array of integers to store user input
int[] userNumbers = new int[5];
System.out.print("Enter " userNumbers.length + " numbers: ");
//Goes into a loop, and sets each array index to the user inputted integer
for (int i = 0; i < userNumbers.length; i++) {
userNumbers[i] = input.nextInt();
}
System.out.println("Enter a number you would like to search for");
boolean exists = false;
int numToSearch = input.nextInt();
//for each number in the user numbers array, check to see if that number matches the number to search. If so, set exists = true and break out of the loop to check no further.
for (int num: userNumbers) {
if (numToSearch == num) {
exists = true;
break;
}
}
//if else to decide which output to show the user.
if (exists) {
System.out.println(numToSearch + " is in the list");
} else {
System.out.println(numToSearch + " is not in the list");
}
}
}

At first instead of storing your numbers in single variables, you store them in an array.
The next thing you'll do is use
boolean tmp = false;
int search = input.nextInt();
This will give you the number the user is searching for.
When you have it (the program will wait at the instruction until there's input), you loop over your array and in each iteration you compare it to the given number. You do this by using
if (array[i] == search) {
tmp = true}
With i being your iteration variable.
After the end of the for loop, you'll do another if where you, depending on the state of the tmp variable either print that the number exists or it doesn't.
Sorry for short explanation.

Try following....
public class NewClass {
public static void main(String[] args) {
java.util.Scanner input = new java.util.Scanner(System.in);
List<Integer> integers = new ArrayList<Integer>();
// Enter three numbers
System.out.print("Enter five numbers: ");
int number1 = input.nextInt();
int number2 = input.nextInt();
int number3 = input.nextInt();
int number4 = input.nextInt();
int number5 = input.nextInt();
integers.add(number1);
integers.add(number2);
integers.add(number3);
integers.add(number4);
integers.add(number5);
System.out.println("The sorted numbers are "
+integers);
System.out.println("Enter a number to search: ");
int searchNum = input.nextInt();
if(integers.contains(seacrchNum)){
System.out.println(searchNum+" is on the list");
}else{
System.out.println(searchNum+" is not on the list");
}
}
Explainations :
Placed all the entered numbers into an arrayLists and then prompt for the search Number to be entered. and Check wheather the search number is der in the ArrayLists or not. Based on the condition display the Message

"exception in thread main java.lang.arrayindexoutofboundsexception" when using an array + for loop

when I wrote this code to prompt the user for how many numbers are going to be entered, I got an error saying: "exception in thread main java.lang.arrayindexoutofboundsexception"
PS: note that I used an array of int + for loop to write it.
import java.util.*;
public class Pr8{
public static void main(String[] args){
Scanner scan = new Scanner (System.in);
//Prompt the user for how many numbers are going to be entered.
System.out.print("*Please write how many numbers are going to be entered: ");
int a = scan.nextInt();
int[] n = new int[a];
for (int i = 0; i < a; i++){
System.out.print("*Please enter an enteger: ");
n[a] = scan.nextInt();
}//for
}//main
}//Pr8

Change
n[a] = scan.nextInt();
to
n[i] = scan.nextInt();
a is not a valid index in an array that only has a elements. The valid indices are 0 to a-1.