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I try to understand nested for loops in javascript but it's very confusing.
I have this code and I can't understand how it works:
let n = 5;
for (let i = 0; i < n; i++) {
for (let j = 0; j < i; j++) {
console.log(j);
}}
In console I have : 0
1
0
1
2
0
1
2
3
And I'm trying to figure out which loop represent each number.
Run this code:
let n = 5;
let str = '';
for (let i = 0; i < n; i++) {
for (let j = 0; j < i; j++)
str += j;
console.log("Outer: "+i+" Inner: "+str);
str = '';
}
Output is:
Outer: 0 Inner:
Outer: 1 Inner: 0
Outer: 2 Inner: 01
Outer: 3 Inner: 012
Outer: 4 Inner: 0123
As you can see, in the output above, inner loop (the one with variable j) doesn't run, because if you replace the variables with numbers it would be
0 < 0 (i < 0), which isn't true.
The best way for you to understand how nested loops work is to write each step and variable values on the paper, like so:
n = 5
STEP 1:
i = 0
i < n (0 < 5) TRUE
j = 0
j < i (0 < 0) FALSE inner loop doesn't execute
OUTPUT: "Outer: 0 Inner:"
str = ''
STEP 2:
i = 1
i < n (1 < 5) TRUE
j = 0
j < i (0 < 1) TRUE
str = 0
j = 1 (j++)
j < i (1 < 1) FALSE
OUTPUT: "Outer: 1 Inner: 0"
str = ''
And so on... Keep repeating this until the argument in the outer loop is false (i < n).
You must remember, in for loop the sequence of orders executed:
for(let i = 0; i < 5; i++) {
console.log('It works');
}
let i = 0; (this executes only once)
i < 5 (if true run 3 and 4)
run the code in loop
i ++
i < 5 (if true run 6 and 7)
run the code in loop
i++
etc.
Related
Using Construct 3 to build a game.
I want to change this function in the code below (which just randomly assigns a frame count in an array) to something that isn't random, but instead loops in order from indexes 0 to 10 and then back to 0 and then to 10 in order again and loop like that continuously.
random(1,Self.AnimationFrameCount)
Is there a random() equivalent for non-random?
// generator function - yields multiple times, maybe forever
function* oneToTenAndBack(N: number): Generator<number> {
while(true) {
for (let i = 0; i < N; i++) yield i;
for (let j = N; j > 0; j--) yield j;
}
}
let k = 0;
for (let num of oneToTenAndBack(4)) {
console.log(num) // 0 1 2 3 4 3 2 1 0 1 2
if (++k>10) break;
}
let gen = oneToTenAndBack(3);
for (let k = 0; k < 10; k++)
console.log(gen.next()) // {value: number, done: false}
Playground Link
I have gone through this Question and Answer While loop inside while loop JavaScript
function getMaxLessThanK(n, k) {
let i = 1;
while (i < n) {
let j = i + 1;
while (j < n + 1) {
console.log(i, j)
j++
}
i++
}
}
when n = 5, what am I getting is
1 2
1 3
1 4
1 5
2 3
2 4
2 5
3 4
3 5
4 5
undefined
How to avoid this the last line undefined. what is the reason for it?
Can anyone help on this please?
Edit:
This is what the actual thing I am doing below.
If you're running it in a console and get an undefined like this：
This undefined indicates that your statement runs without returning a value. It's not a result of your console.log.
If you make the function return something:
function getMaxLessThanK(n, k) {
let i = 1;
while (i < n) {
let j = i + 1;
while (j < n + 1) {
console.log(i, j)
j++
}
i++
}
return 'return value';
}
Then you'll get
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I am trying to make a Javascript pattern that accepts a user input in the form of a digit and returns the below output:
******1
****1 2 1
***1 2 2 1
**1 2 3 2 1
*1 2 3 3 2 1
1 2 3 4 3 2 1
*1 2 3 3 2 1
**1 2 3 2 1
***1 2 2 1
****1 2 1
*****1
However I am stuck at the a pattern that looks like this:
1
1 2 1
1 2 3 2 1
1 2 3 4 3 2 1
1 2 3 2 1
1 2 1
1
This is the code I wrote until now.
function selectNo() {
var selectedNo = document.getElementById("select-number").value;
for (var i = 1; i <= selectedNo; i++) {
for (var l = 0; l < (selectedNo - i); l++)
document.write(" ")
for (var j = 1; j <= i; j++)
document.write(" " + j)
for (var k = i - 1; k >= 1; k--)
document.write(" " + k)
document.write("<br>");
}
for (var i = 1; i <= selectedNo; i++) {
for (var l = 0; l < i; l++)
document.write(" ")
for (var j = 1; j <= (selectedNo - i); j++)
document.write(" " + j)
for (var k = selectedNo - i - 1; k >= 1; k--)
document.write(" " + k)
document.write("<br>");
}
}
<input type="number" id="select-number" placeholder="Select your number">
<button onclick="selectNo()">Print the pattern</button>
Any suggestions on how to reach the target pattern? Thank you!
Create a function that returns the array of the next numbers and then you can loop from 1 to the input number.
Then you just need to join the arrays.
function line(len) {
const middle = (len - 1) / 2;
const a = [];
for(let i = 0; i < len; i++) {
if(i < middle) {
a.push(i + 1);
}
else {
a.push(len - i);
}
}
return a;
}
function diamond(len) {
l = len * 2 - 1;
const d = [];
for(let i = 0; i < l; i++) {
const a = line(i + 1).map(v => `${v} `);
const b = new Array(l - a.length).fill(' ').concat(a).join('');
d.push(b);
}
for(let i = l - 2; i >= 0; i--) {
const a = line(i + 1).map(v => `${v} `);
const b = new Array(l - a.length).fill(' ').concat(a).join('');
d.push(b);
}
return d.join('<br/>');
}
function main() {
document.getElementById("result").innerHTML = diamond(document.getElementById("val").value);
}
<input id="val" type="number" placeholder="Select your number">
<button onclick="main()">Print the Pattern</button>
<div id="result" style="font-family: monospace;"></div>
I have the following loop:
for (let i=0; i<7; i+=2) {
for (let j=i; j<i+2; j++) {
console.log(j);
}
console.log('\n');
}
If I execute it I get:
0
1
2
3
4
5
6
7
But it only works on even conditions (0-7 = 8), if I instead put i<8, I get the same:
0
1
2
3
4
5
6
7
Which is bad, it must has returned 8 at the end, but instead doesn't print it. I expect my result when the condition is not even like this:
0
1
2
3
4
5
6
7
8
How can I achieve it? Thanks for your help.
You could use a single loop and add for each odd value a line feed after printing the value.
for (let i = 0; i <= 8; i++) {
console.log(i);
if (i % 2) {
console.log('\n');
}
}
Although Nina's answer is better, for completeness, I post a corrected version of the code that you started with:
let n = 8;
for (let i=0; i<=n; i+=2) {
for (let j=i; j<i+2 && j <= n; j++) {
console.log(j);
}
console.log('\n');
}
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so this is what I've achieved so far
function arrayMode(sequence) {
var arr= [];
var mostFreq = 1;
for(var i = 1; i <= 10; i++)
arr[i] = 0;
for(var i = 0 ; i < sequence.length; i++)
arr[sequence[i]]++;
for(var i = 1; i < 10; i++){
if( arr[i] > arr[mostFreq])
mostFreq = i;
}
return mostFreq;
}
so the scope for my case are
The sequence value is >= 1 and <=10
The sequence length is > 0
The sequence is an array of integer
Example 1
Input : sequence = [1, 10, 10]
Output : 10
Example 2
Input : sequence = [1, 3, 3, 3, 1]
Output : 3
It seems easy, I've tried to figure out but I cant find where is the mistake in my code, It's seems legit for me
As suggested by Maxim Krizhanovsky, the last loop should go from 1 to 10 instead of to sequence.length. Here is the working code
function arrayMode(sequence) {
var arr= [];
var mostFreq = 1;
for(var i = 0; i <= 10; i++)
arr.push(0);
for(var i = 0 ; i < sequence.length; i++)
arr[sequence[i]]++;
for(var i = 1; i <= 10; i++){
if( arr[i] > arr[mostFreq])
mostFreq = i;
}
return mostFreq;
}
The output is 10 and 3 respectively to your input.