This program I am writing is giving me fits. What I am trying to do is prevent a user from entering the same integer twice. The program takes 4 int inputs and compares them to an array of 4 random int's, searching for a match. Here is what I have thus far in my attempts to prevent multiple inputs.
for (int z = 0; z<4; z++){
System.out.println("Enter a number between 0-9. No duplicates please!");
temp[z] = inputDevice.nextInt();
for(int why = 0; why<temp.length; why++){
if(Arrays.asList(temp).contains(temp[z])){
System.out.println("Duplicate found! Please enter a non-repeating digit");
temp[z]=0;
z--;
}
}
}
The inputs are coming into the temp array just fine. And are being passed on to the other methods in the program, and that is working. I am guessing the issue is with my conditional statement - if(Arrays.asList(temp).contains(temp[z]))
Is there a better way to test to see if an array already contains a value?
Thanks in advance.
1) Since you are converting the array to a list, might as well use an ArrayList
2) Store your input in a variable and test if it is contained within the list already
List<Integer> my_list = new ArrayList<Integer>();
for (int z = 0; z<4; z++){
System.out.println("Enter a number between 0-9. No duplicates please!");
int input = inputDevice.nextInt();
if(my_list.contains(input)){
System.out.println("Duplicate found! Please enter a non-repeating digit");
z--;
}
else{
my_list.add(input);
}
}
When you check if temp contains z, it already contains z. Put the input in a temporary variable before you check it and only add it afterwards.
You're not using the why from your loop.
However if possible I would change temp to an ArrayList implementation. The problem with toList method. It's using the int[] array as a single object rather than treating it as an array of int objects. To do the latter you must use Integers.
Related
I am new to JAVA and this is what I have to do:
Accept a set of marks (out of 100). The user should press the Enter button after each mark is entered and the mark should then be added to an ArrayList of Integers.
This is what I have so far:
int score = Integer.parseInt(marksinput.getText());
ArrayList<Integer> marks = new ArrayList();
Collections.addAll(marks, score);
String out = "";
String Out = null;
int[] studentmarks = {score};
for (int item : studentmarks) {
marksoutput.setText(""+item);
}
if (score > 100) {
marksoutput.setText("Enter marks\n out of 100");
}
This only adds one mark in the arraylist and I need user to input as many marks he wants. I know that my arraylist is wrong, which is why it only takes 1 number but I do not know how to make all the input numbers go in arraylist. What I have is that it takes the number and if user inputs another number, it just replaces the older number. I want it to display both the numbers not just one. Any help is appreciated and thank you in advance!☻☻
(This is not a duplicate even though others have the same title)
In case what you are after is a program that adds any integer typed by the user into an ArrayList, what you would have to do is the following:
Scanner scanner = new Scanner(System.in);
List<Integer> ints = new ArrayList<Integer>();
while(true)
ints.add(scanner.nextInt());
What this program will do, is let the user input any number and automatically puts it into an ArrayList for the user. These integers can then be accessed by using the get method from the ArrayList, like so:
ints.get(0);
Where the zero in the above code sample, indicates the index in the ArrayList from where you would like to retrieve an integer.
Since this website is not there to help people write entire programs, this is the very basics of the ArrayList I have given you.
The ArrayList is a subclass of List, which is why we can define the variable using List. The while loop in the above example will keep on going forever unless you add some logic to it. Should you want it to end after executing a certain amount of times, I would recommend using a for loop rather than a while loop.
Best regards,
Since it seems you are really new,
What you are looking for is a for-loop
From the Java documentation, he is the syntax of a for-loop in Java
for (initialization; termination; increment) {
statement(s)
}
Initialization: Obviously you want to start from 0
Termination: you want to stop after 100 inputs, so that's 99 (starting from zero)
Increment: you want to "count" one by one so count++
for(int counter = 0; counter < 100; counter++) {
//Ask user for input
//read and add to the ArrayList
}
So before you enter the for-loop you need to initialize the ArrayList, and a Scanner to read input:
Scanner sc = new Scanner(System.in);
ArrayList<Integer> list = new ArrayList();
for(int counter=0; counter < 100; counter++) {
System.out.println("please enter the " + counter + " number");
int x = sc.nextInt();
list.add(x);
}
I have an issue for creating an array based on the total amount of numbers entered into the array.
Essentially the program is expected to work as the following: the user is prompted for n numbers to enter into an array. So until the user types '000' as their input, the user will be prompted for a new number.
Note: for this array, I do not want the user to input the amount of numbers they want to enter for the array size. Instead, I want the user to continue inputting random numbers until '000' has been inputted, then, the total amount of numbers that has been entered into the array, is the size of such array.
For example: this would work if we have int array[] = {1, 2, 4, 6}, this will automatically set array size to 4, without actually explicitly declaring the array size as 4 elements. Similarly, with my code, I want it where the numbers that the user enters is added to the array, and then the array size is automatically given from the amount of numbers the user has entered like above.
It is important to note that we do not know the length of the array until the user has entered all n numbers.
I have attempted a skeleton, but it returns a cannot find symbol error:
Code:
//Array Code
import java.util.*;
class setArray {
public static void main(String[] args) {
Scanner input = new Scanner(System.in);
int stopInput = 000;
int number;
System.out.print("Enter a number: ");
number = input.nextInt();
while(number != stopInput) {
System.out.print("Enter a number: ");
number = input.nextInt();
int array[] = {number};
}
System.out.print("Array size: " + array.length);
} // Main brace
} // Class brace
setArray.java:19: error: cannot find symbol
System.out.print("Array Size: " + array.length);
symbol: variable array
location: class setArray
1 error
You have a few errors here. The first is understanding why you get your immediate error. The variable array is declared within the scope of the while loop. It can not be seen outside of this loop. That is why the compiler is complaining.
The second is that the size of the array (if declared outside of the loop) will always be 1. From my understanding of what you have written as an attempt to solve the problem you have describe shows that you are not tackling the problem correctly.
While you don't known the the final length of the array to be entered; you do need to store the values entered (my inference) to populate the final array. To store the value entered by the user you need a list that will grow with the input.
List<Integer> values = new ArrayList<>();
while (number != stopInput) {
System.out.print("Enter a number: ");
values.add(Integer.valueOf(input.nextInt()));
}
Integer[] array = values.toArray(new Integer[values.size()]);
Firstly, the compilation error is because the array variable is not visible from the System.out.println line. This is because it's declared inside the while loop, so is only visible inside the while loop.
To make it visible to the whole method, declare it before the while loop.
Secondly, arrays cannot be resized. You declare an array to be a certain size, and you cannot add or remove elements.
My suggestion would be to use an ArrayList. Declare one before your loop, and add the new number inside the loop. After the loop, the size should be how many numbers were entered.
Finally, there's no difference between 000 and 0. Is 0 a valid input number?
You can use
List<Integer> array=new ArrayList<Integer>();
while(number != stopInput) {
System.out.print("Enter a number: ");
number = input.nextInt();
array.add(number);
}
This sounds like a job for java.util.ArrayList - this is the array that doesn't have a fixed size and is growing as you add values to it automatically under the covers.
The error is caused because you are creating the array only within the scope of the while loop. You need to create it outside the loop. Secondly, standard arrays are not dynamic, so you would need to either set the size and increase it as needed, or just simply use an ArrayList.
Psuedo:
ArrayList<Integer> list = new ArrayList<Integer>()
...
while(not stop number)
list.add(number)
...
print(list.size())
If you really want to use an Array, here is how you can do it
public static void main(String[] args){
STOP_ENTRY = "000";
scan = new Scanner(System.in);
entry = "";
while(true){
System.out.print("Enter #: ");
String tempS = scan.nextLine();
if(tempS.equals(STOP_ENTRY)) break;
else entry += tempS + ":";
}
String[] split = entry.split(":");
int[] intArray = new int[split.length];
System.out.println("Length of created intArray = " + intArray.length); //length of created array
for(int i = 0; i < intArray.length; i++){
intArray[i] = Integer.parseInt(split[i]);
System.out.println("intArray[" + i + "] => " + String.valueOf(intArray[i]));
}
}
I would recommend an ArrayList, as it dynamically changes is size when you add an element, but do whatever you'd like.
An important note, this does not handle any malicious entry that you might not want (characters, symbols), and will error if they are entered, something you can easily add if you need
I am making a program that prompts the user for 3 integers and prints out the biggest one chosen. I am stuck with 2 problems at the moment. I would like to know how I can make the program so that the user can only choose integers from the array. I would also like to know how to find and print out the biggest integer from the ones that the user chose. I'm quite new to programming so all feedback is appreciated.
Thanks!
import java.util.Scanner;
public class Lab14C // name of class file
{
public static void main(String [] args)
{
int[] array = {0,1,2,3,4,5,6,7,8,9};
for(int i=0; i<array.length; i++)
{
System.out.print(array[i] + " ");
}
System.out.println("\n");
Scanner array1 = new Scanner(System.in);
System.out.println("What is your first integer? ");
double array11 = array1.nextInt();
Scanner array2 = new Scanner(System.in);
System.out.println("What is your second integer? ");
double array22 = array2.nextInt();
Scanner array3 = new Scanner(System.in);
System.out.println("What is your third integer? ");
double array33 = array3.nextInt();
System.out.println("\n");
}
}
I don't think there is a way to force a user to input an element. Few things you could do is :
Tell the user he has to select a number in a particular range.
Keep the input statement in a loop. If the entered element exists in array , go ahead. Else tell the user to enter again.
Printing the biggest integer can be done using Math.max(double,double) function. For three elements you can try System.out.println("Max of three is "+Math.max(array11,Math.max(array22,array33)))
You can do it yourself if you want instead of built in function like:
if(array1>array2&&array1>array3)
//print max as array1
else if(array2>array1&&array2>array3)
//print max as array2
else //print array3 as max
Also change your element types to int as you are reading integer.
1) There is no need to create a new Scanner all the time.
Just create one Scanner (which I would just call input or scanner or something that makes sense).
2) If you're reading int's why are you storing them in doubles?
3) To check for a certain condition you use if(*condition*) { /*do something */ }. So if you want to check if x is smaller than y you do if(x < y) { /* do something */ }. (In your case you'll want to check if current input is greater than biggest input and if so set the biggest input to current input.)
4) For a sorted array you can use Arrays.binarySearch(array, elementToSearch) which will return the index of the element when found, or a negative number if not found (the negative number is (-(insertionPoint)-1)). (So you can check if the number entered by the user is in the array and keep asking for a new number if is not.)
1) How I can make the program so that the user can only choose integers from the array.?
You are declaring array variable as int[] so it stores only integer values. Whenever you retrives the value from this array, it returns int value only so you don't have to worry about it.
2)how to find and print out the biggest integer from the ones that the user chose.?
To find the maximum or minimum from a set of values, Java provide a function name Math#max(). You can use it like this :
int maxValue = Math.max(Math.max(array11,array22),array33);
Here is the doc for Math library.
I am making an inefficient calculator type of program that takes values from user defined arrays and plugs them into an equation that the user also defines. To do this I needed to make my program change my string to a char array, the problem? I have it so that users must use A1-10 to reference the definded index and I cannot find a way to make the program search the next array for the number to specify what array the program is accessing.
out.println("Please input a string of commands in a format similar to this: ");
out.println("([A1]-[A2]=) or ([A8]+[A6]=) or ([A1]-[A4]+[A7]*[A10]/[A3]=)");
out.println("Use only the numbers 1-10 when referencing an array. \n You may always type in 'Help' if you need help. ");
String eString = scn.nextLine();
if ("help".equals(eString)) {
out.println("Figure it our yourself...");
} else {
for (char c: eString.toCharArray()) {
if (c == 'A') {
}
}
the code got a little jumbled up while changing code and I haven't taken the time to make it look nice and pearly again.
If you need the index you should just use a normal for loop instead of an enhanced for loop.
char[] input = eString.toCharArray();
for(int i = 0; i < input.length; i++) {
if(input[i] == 'A'){
// You know the index of A here.
}
}
You should also use "help".equalsIgnoreCase(eString) when comparing with help so that they can enter either "Help" or "help" (link to doc)
i am trying to run a very simple java program. i want to write a program that reads 10 integers and that the programs finds witch one is the maximum of them.
i wonder if is possible that inside a loop i can read the 10 values.
Scanner input = new Scanner (System.out);
int num1, num2, num3, num4, num5, num6, num7, num8, num9, num10;
System.out.print(" please enter the numer " +i);
===>num[i] = input.nextInt();//
i am trying to find the way to do it without using an array, since i haven't see this in school yet.
any idea how to do it inside a loop? or is just no possible to do?
Sure it's possible.
All you have to do is keep the current maximum value, and then compare it to the value entered by the user for every new value he enters.
You can use the for loop to make sure it runs exactly 10 times.
For that you will have to create int array of 10 length and then read that intvalues in loop and process further.
Example :-
Scanner input = new Scanner (System.out).useDelimiter("\n");
int values[] = new int[10];
.
.
.
for ( int i = 0 ; i < values.length ; i++ ){
System.out.print(" please enter the numer " +i);
values[i] = input.nextInt();
}
If all you need is the maximum value, you don't need to store all ten inputs. So yes, this is possible without an array, and you don't need 10 integer variables either.
(Think about it a bit, you'll see that you can find the maximum in an array by scanning it once. Then you don't need the array anymore.)