freeCodeCamp/guide/english/certifications/javascript-algorithms-and-data-structures/debugging/use-caution-when-reinitializing-variables-inside-a-loop/index.md

title
Use Caution When Reinitializing Variables Inside a Loop

Use Caution When Reinitializing Variables Inside a Loop

• This challenge must be solved by redefining the scope of row[].
• Below is an example of the desired matrix.

[
[0][0],
[0][0],
[0][0]
]

• However the current matrix - seen below - is far from the desired matrix

[
[0][0][0][0][0][0],
[0][0][0][0][0][0],
[0][0][0][0][0][0]
]

• This error occurs due to the row[] array being declared as a global variable outside of the nested for loop.
• However, to fill the matrix correctly the row[] array must be reset after each iteration of the outer loop.

Solution

function zeroArray(m, n) {
  let newArray = [];
  for (let i = 0; i < m; i++) {
     let row = []; /* <-----  row has been declared inside the outer loop. 
     Now a new row will be initialised during each iteration of the outer loop allowing 
     for the desired matrix. */
    for (let j = 0; j < n; j++) {

      row.push(0);
    }
    newArray.push(row);
  }
  return newArray;
}
let matrix = zeroArray(3, 2);
console.log(matrix);