I need to insert randomly generated numbers into an array

Question

I've looked through the questions with similar words or intent, but can't seem to find one that would help me.

I have created an array using user input, I need to generate numbers between 100 and 10000 and insert it into the array. I have created the array, it shows as filled with zeroes, and I have generated the random numbers, but I can't seem to insert the randomly generated numbers into the array.

Here's my code so far.

import java.util.*;

public class Print2DArray {

    public static void main(String[] args) {

        System.out.println();
        Scanner userInput = new Scanner(System.in);

        System.out.println("Enter the number of rows");
        int rows = userInput.nextInt();

        System.out.println("Enter the number of columns");
        int columns = userInput.nextInt();

        int[][] array = new int[rows][columns];
        for (int a = 0; a < rows; a++)
            for (int b = 0; b < columns; b++)
                array[a][b] = 0;

        for (int i = 0; i < rows; i++) {
            for (int j = 0; j < columns; j++) {
                System.out.print(array[i][j]);
                {
                    Random r = new Random();
                    int rand = r.nextInt(10000 - 100) + 100;
                }
            }
            System.out.println();
        }
    }
}

Answer 1

import java.util.Random;
import java.util.Scanner;

public class QuickTester {

    public static void main(String[] args) {

        Scanner userInput = new Scanner(System.in);

        System.out.print("Enter the number of rows: ");
        int rows = userInput.nextInt();

        System.out.print("Enter the number of columns: ");
        int columns = userInput.nextInt();

        // Create the Random instance once here!
        Random rand = new Random();
        int[][] array = new int[rows][columns];
        for (int a = 0; a < rows; a++)
            for (int b = 0; b < columns; b++)
                array[a][b] = rand.nextInt(10000 - 100) + 100;

        for (int i = 0; i < rows; i++) {
            for (int j = 0; j < columns; j++) {
                System.out.print(array[i][j] + " ");
            }
            System.out.println();
        }   
    }
}

Input/Output:

Enter the number of rows: 3
Enter the number of columns: 2
574 5286 
1550 5259 
8343 4877

Note:

• Create the Random only once, not in every iteration of the double for loop
• If you want 100 to 10000 (inclusive), it needs to be nextInt(10000-100+1) + 100
• Random#nextInt(int n) gives you [0, 9990) or [0, 9989] so the biggest value you will get from your expression is 9999, and not 10000

Answer 2

array[i][j] = r.nextInt(10000 - 100) + 100;

Answer 3

You are not assigning rand to array element. Your 2nd for loop should be

Random r = new Random();
for(int i = 0; i<rows; i++)
{
    for(int j = 0; j<columns; j++)
    {

        array[i][j] = r.nextInt(900) + 100;
        System.out.print(array[i][j] + " ");
    }
    System.out.println();
}

Answer 4

You need 3 things to do,

• Assign the random value into the array.

• Use only one nested for loop 's.

• Do not initialize Random r inside the loop.

Try this:

int[][] array = new int[rows][columns];
Random r = new Random();    
for (int a = 0; a < rows; a++)
    for (int b = 0; b < columns; b++) {
        array[a][b] = r.nextInt(10000 - 100) + 100;
        System.out.print(array[a][b]);
    } 
    System.out.println();
}