Randy Rivera

Posted on

Using Caution When Reinitializing Variables Inside a Loop

• Sometimes it's necessary to save information, increment counters, or re-set variables within a loop. A potential issue is when variables either should be reinitialized, and aren't, or vice versa. This is particularly dangerous if you accidentally reset the variable being used for the terminal condition, causing an infinite loop.
• Printing variable values with each cycle of your loop by using `console.log()` can uncover buggy behavior related to resetting, or failing to reset a variable.
• Ex: The following function is supposed to create a two-dimensional array with `m` rows and `n` columns of zeroes. Unfortunately, it's not producing the expected output because the `row` variable isn't being reinitialized (set back to an empty array) in the outer loop. Fix the code so it returns a correct 3x2 array of zeroes, which looks like `[[0, 0], [0, 0], [0, 0]]`.
• Code:
``````function zeroArray(m, n) {
// Creates a 2-D array with m rows and n columns of zeroes
let newArray = [];
let row = [];
for (let i = 0; i < m; i++) {
// Adds the m-th row into newArray

for (let j = 0; j < n; j++) {
// Pushes n zeroes into the current row to create the columns
row.push(0);
}
// Pushes the current row, which now has n zeroes in it, to the array
newArray.push(row);
}
return newArray;
}

let matrix = zeroArray(3, 2);
console.log(matrix); console will display
[ [ 0, 0, 0, 0, 0, 0 ],
[ 0, 0, 0, 0, 0, 0 ],
[ 0, 0, 0, 0, 0, 0 ] ]
``````
• Fixed:
``````function zeroArray(m, n) {
// Creates a 2-D array with m rows and n columns of zeroes
let newArray = [];
for (let i = 0; i < m; i++) {
// Adds the m-th row into newArray
let row = []; <----------
for (let j = 0; j < n; j++) {
// Pushes n zeroes into the current row to create the columns
row.push(0);
}
// Pushes the current row, which now has n zeroes in it, to the array
newArray.push(row);
}
return newArray;
}

let matrix = zeroArray(3, 2);
console.log(matrix); will now display
[ [ 0, 0 ], [ 0, 0 ], [ 0, 0 ] ]
``````