Question

Java programming language

Array - Single identifier which can store multiple values

Example initialized with values: int[] mySimpleArray = {4, 17, 99};

Example with fixed length but no values: int[] myFixedArray = new int[11];

The brackets identify the index. Each value has its own index number.
NOTE: First element is the zeroth element: mySimpleArray[0] is 4, [1] is 17

Make a new Netbeans project called ArraysAndLoops

Create the simple array with 4, 17, 99.

Use System.out.println with the variable with index literals to print out each value.

MORE LOOPS - Computing factorials

Show how factorial algorithm works, use FOR loop for factorials 0 to 10

Use i as index to store each factorial in an array

Use method Array.toString(myFactorials) to print out array at each step to check

          NOTE: requires import java.util.*

WRITING A FILE - requires import java.io.*

Step 1: Make an object for file output

Step 2: Use object, method println(...)

In-Class Active: Print the factorials array to a .txt file

          PrintWriter objectName = new PrintWriter(file path.filename);

Apply that structure to the array already made; use objectName factorialsTest

          Make a header statement for the first line of the file:

                   factorialsTest.println("Factorials 0 to 10");

Make the next line the array with all its values:

          factorialsTest.println(Arrays.toString(myFactorials));

These println method put the Strings in a buffer. Write to actual file by closing object.

          factorialsTest.close();

If time, print out all the array values using a FOR loop, System.out

Answer 1

Java Code:

package arrayprog;

//Imports
import java.io.FileNotFoundException;
import java.io.PrintWriter;
import java.util.*;

public class ArraysAndLoops {
   //Main method
   public static void main(String[] args) throws FileNotFoundException {
       //Initializing an array
       int arr[] = {4, 17, 99};
       //Printing the array using the index
       System.out.println(arr[0]);
       System.out.println(arr[1]);
       System.out.println(arr[2]);
      
       //Declaring an array to store factorials
       int myFactorials[] = new int[11];
       myFactorials[0] = 1; //0! is 1
       System.out.println("Factorial values: ");
       //Factorial algorithm
       for(int i = 1 ; i <= 10 ; i++) {
           myFactorials[i] = i * myFactorials[i-1]; //factorial(i) = i * factorial(i-1)
           System.out.println(Arrays.toString(myFactorials)); //printing the array at each iteration
       }
       //Writing to a file using a PrintWriter
       PrintWriter factorialsTest = new PrintWriter("C:\\Users\\vkanchan\\pro\\Ques\\src\\arrayprog\\factorials.txt");
       factorialsTest.println("Factorials 0 to 10");
       factorialsTest.println(Arrays.toString(myFactorials));
       //Closing the file
       factorialsTest.close();
   }

}

Sample Output:

4
17
99
Factorial values:
[1, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0]
[1, 1, 2, 0, 0, 0, 0, 0, 0, 0, 0]
[1, 1, 2, 6, 0, 0, 0, 0, 0, 0, 0]
[1, 1, 2, 6, 24, 0, 0, 0, 0, 0, 0]
[1, 1, 2, 6, 24, 120, 0, 0, 0, 0, 0]
[1, 1, 2, 6, 24, 120, 720, 0, 0, 0, 0]
[1, 1, 2, 6, 24, 120, 720, 5040, 0, 0, 0]
[1, 1, 2, 6, 24, 120, 720, 5040, 40320, 0, 0]
[1, 1, 2, 6, 24, 120, 720, 5040, 40320, 362880, 0]
[1, 1, 2, 6, 24, 120, 720, 5040, 40320, 362880, 3628800]

factorials.txt:

Factorials 0 to 10
[1, 1, 2, 6, 24, 120, 720, 5040, 40320, 362880, 3628800]