Read matrix elements and print them

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I created an algorithm that would receive a single variable with 9 different records that would display these values typed in matrix form (table). But when displaying the result, it is only returning the last three values in three lines in a row.

var numero = Array(3,3);
  var x,y;
  for (x = 0; x < 3; x++) {
    for (y = 0; y < 3; y++) {
      numero[x,y] = parseInt(prompt("Digite o "+[y+1]+"º número da "+[x+1]+"º coluna"));
    }
  }
  for (x = 0; x < 3; x++) {
    for (y = 0; y < 3; y++) {
      document.write(numero[x,y]+"&nbsp&nbsp");
    }
    document.write("<br>");
  }

In this case, what would be the most correct way to display the 9 values that the user correctly typed and in matrix form?

javascript array matrix
  • 1

    Declaration. In Javascript we do not create an array with Array(3, 3). See the documentation on MDN. And you also don’t access a position with [x, y], you need to create a array of array.

  • This documentation did not make my doubt very clear, because in a coordinate axis, I thought the syntax of the Array could be written in parentheses (). I noticed some articles here on the internet, but I couldn’t come up with any conclusions regarding this syntax made with brackets [][] which is quite different from what I learned in theory. You could put a practical example about this syntax?

1 answer

1


As explained in the comments, in accordance with the documentation, when you do Array(3,3), you are creating an array with 2 elements (and both elements are the number 3):

let arrayCom2Elementos = Array(3, 3);
// array com 2 elementos
console.log(arrayCom2Elementos); // [3, 3]
// tamanho do array
console.log(arrayCom2Elementos.length); // 2

In native Javascript there are no matrices per se (although there are libraries for this), but you can simply create an array of arrays: first you create an array, and then you make each element of it also an array.

For this you can use Array(3), because according to the documentation, when only a number is passed to the constructor, this is used as the array size.

Then you loop this array, and make each element another array of 3 elements:

let matriz = Array(3); // array com 3 elementos

// cada elemento é outro array com 3 elementos
for (let i = 0; i < matriz.length; i++) {
  matriz[i] = Array(3);
}
console.log(matriz); // cada elemento é um array de 3 elementos

Another detail is that, to access the elements of the "matrix" (which is actually an array of arrays), the syntax is not used [x, y]. First you do matriz[x], which returns the position array x. And how matriz[x] is also an array, to access the position y of it just make matriz[x][y].

In short, your code would look like this:

let dimensao = 3; // dimensão da matriz (assumindo que ela é uma matriz quadrada)
let matriz = Array(dimensao); // array com 3 elementos

// cada elemento é outro array com 3 elementos
for (let i = 0; i < matriz.length; i++) {
  matriz[i] = Array(dimensao);
}

let linha, coluna;
for (linha = 0; linha < dimensao; linha++) {
  for (coluna = 0; coluna < dimensao; coluna++) {
    matriz[linha][coluna] = parseInt(prompt("Digite o " + (linha + 1) + "º número da " + (coluna + 1) + "º coluna"));
  }
}

for (linha = 0; linha < dimensao; linha++) {
  for (coluna = 0; coluna < dimensao; coluna++) {
    document.write(matriz[linha][coluna] + "&nbsp&nbsp");
  }
  document.write("<br>");
}

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