Java: How do I store a vector in another vector and using Math library

Question

my doubt is the following, I have to read 20 integer numbers in one vector and then I have to compute the square of that vector and store in another and then display the two.

But when it comes to square I use a java library that is Math the code is like this at the time of calculating:

import java.util.Scanner;

public class Exercicio01Lista { 
   public static void main(String[] args) { 
      int [] num = new int[5]; 
      int [] num2 = new int[5]; 
      Scanner entrada = new Scanner(System.in); 
      for (int c = 0; c<num.length; c++) { 
         System.out.println("Numero: "); 
         num[c] = entrada.nextInt(); 
      } 
      for (int i = 0; i<num2.length; i++) { 
         num2[i] = Math.sqrt(num[c]); 
      } 
   } 
}

only that it is giving error.

Answer 1

You can do a for that traverses your array and stores n² in the new array like this:

for (int i = 0; i<arrayValores.length, i++){
   int arrayQuadrado[i] = pow(arrayValores[i],2);
}

Answer 2

The variable c is only visible in the first for, but since arrays have the same size you can use the variable i for the two arrays.

    public static void main(String[] args) {
        int[] num = new int[5];
        int[] num2 = new int[5];

        Scanner entrada = new Scanner(System.in);

        for (int c = 0; c < num.length; c++) {
            System.out.println("Numero: ");
            num[c] = entrada.nextInt();
        }

        for (int i = 0; i < num2.length; i++) {
            num2[i] = (int) Math.pow(num[i], 2);
        }

        entrada.close();
    }

Answer 3

Using Java 8+, you can generate the array with the squares in a single row. Assuming your array is the variable numeros, then you can do it:

int[] quadrados = IntStream.of(numeros).map(x -> x * x).toArray();

To read the 20 numbers, you can also do it with two lines:

Scanner entrada = new Scanner(System.in);
int[] numeros = IntStream.generate(entrada::nextInt).limit(20).toArray();

To display the array, you can do it in a row as well:

System.out.println(Arrays.toString(quadrados));

Here is the resulting complete code. Note that it is very simple, only needs 5 lines between the { and the } of the method main:

import java.util.Arrays;
import java.util.Scanner;
import java.util.stream.IntStream;

class Teste {
    public static void main(String[] args) {
        Scanner entrada = new Scanner(System.in);
        int[] numeros = IntStream.generate(entrada::nextInt).limit(20).toArray();
        int[] quadrados = IntStream.of(numeros).map(x -> x * x).toArray();
        System.out.println(Arrays.toString(numeros));
        System.out.println(Arrays.toString(quadrados));
    }
}

Given this input:

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20

This output is produced:

[1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20]
[1, 4, 9, 16, 25, 36, 49, 64, 81, 100, 121, 144, 169, 196, 225, 256, 289, 324, 361, 400]

See here working on ideone.

Ah, Math.sqrt(...) is to compute the square root. To compute the square, the simplest way is to multiply each element by itself as in the code above. Note that the code to create the array with the squares works regardless of the size of the original array.

If you want a message to appear to ask for the number, you can do something like this:

int[] numeros = IntStream.generate(() -> {
    System.out.println("Digite um número: ");
    return entrada.nextInt();
}).limit(20).toArray();

Answer 4

int exchange for double.

int [] num = new int[5]; double [] num2 = new double[5];

     Scanner entrada = new Scanner(System.in); 
     
      for (int i = 0; i < num.length; i++) { 
         System.out.println("Numero: "); 
         num[i] = entrada.nextInt(); 
      } 
      for (int i = 0; i<num2.length; i++) { 
         num2[i] = Math.sqrt(num[i]); 
      } 
      
      for (int i = 0; i<num2.length; i++) { 
          System.out.println("A raiz quadrada do número "+num[i]+" é "+num2[i]);
      }