Develop Reference

How to push both sum of even and odd result from for loop into an array?

Use for loop to iterate from 0 to 100 and print the sum of all evens and the sum of all odds. Print sum of evens and sum of odds as array
Output: [2550, 2500]
let sumOfEven = 0;
let EvenOddArr = [];
for (let i = 0; i <= 100; i += 2) {
sumOfEven += i;
}
console.log(sumOfEven);
let sumOfOdd = 0;
for (let i = 1; i <= 100; i += 2) {
sumOfOdd += i;
}
console.log(sumOfOdd);
console.log(EvenOddArr);

You could take the remainder of two as index for the array.
const evenOddArr = [0, 0];
for (let i = 0; i <= 100; i++) evenOddArr[i % 2] += i;
console.log(evenOddArr);

You're nearly there - all you need is a couple of pushes
let sumOfEven = 0;
let EvenOddArr = [];
for (let i = 0; i <= 100; i += 2) {
sumOfEven += i;
}
EvenOddArr.push(sumOfEven)
let sumOfOdd = 0;
for (let i = 1; i <= 100; i += 2) {
sumOfOdd += i;
}
EvenOddArr.push(sumOfOdd)
console.log(EvenOddArr);

console.log(Array(101).fill().reduce((a,_,i)=>(a[i%2]+=i,a),[0,0]))

Here is an alternative for when you have studied JS a bit more
let sumArr = Array.from({ length: 101 })
.reduce((acc,_,i) => (acc[i % 2] += i, acc), [0, 0]);
console.log(sumArr);

An easy-to-understand version:
let sumOfEven = 0;
let sumOfOdd = 0;
for (let i = 0; i <= 100; i++) {
if (i % 2 === 0) {
sumOfEven += i;
} else {
sumOfOdd += i;
}
}
let evenOddArr = [sumOfEven, sumOfOdd];
console.log(evenOddArr);

Can't make pyramid of numbers

I Need to get this output:
1
2 3
4 5 6
7 8 9 10
11 12 13 14 15
What I've tried so far:
function getPyramid() {
let nums = 0;
for (let i = 1; i <= 15; i++) {
for (let n = 1; n < i; n++) {
console.log(n);
}
console.log('<br/>');
}
return nums;
}
getPyramid();

It is possible to do with one single loop
function getPyramid() {
let nums = 0;
let count = 1;
let numbers = ''
for (let i = 0; i <= 15; i++) {
if(count === nums){
count++
nums = 0;
console.log(numbers)
numbers = ''
}
nums ++
numbers += ' ' + (i +1)
}
}
getPyramid();
Or like this you can specify amount of rows..
function getPyramid(rows) {
let nums = 0;
let count = 1;
let numbers = ''
let i = 1
while (count < rows + 1 ) {
if(count === nums){
count++
nums = 0;
console.log(numbers)
numbers = ''
}
nums ++
numbers += ' ' + i
i++;
}
}
getPyramid(5);

for (let i = 1 ; i <= 5; i++)
{
let s = []
for (let x = i * (i - 1) / 2 + 1; x <= i * (i + 1) / 2; x++)
{
s.push(x)
}
console.log(s.join(" "))
}

Apart from notes given by jnpdx in the comments, I'd add some:
for better convention between programmers we tend to name varible nested in for-loop: i, j
<br/> for HTML new line, In JS we do \n for that!
number++ is same number += 1
Conditional_Operator (expression)?true:false instead of if/else
function getPyramid(Lines) {
let number = 1; // the counter to display on each line of pyramid!
for (let i = 1; i <= Lines; i++) {
let str = '';//line to display
for (let j = 1; j <= i; j++) {
str += number++;//incrementing counter
str += j!=i ? ' ' : ''; //to make space, but not at the end of line.
}
console.log(str);//display that line
}
}
getPyramid(5);

A completely unnecessary attempt to do this in a functional style:
const ranged_array = (from, to) =>
Array.from({ length: to - from + 1 }, (_, i) => i + from);
const pyramid = (lines) =>
ranged_array(1, lines)
.reduce((a, v, i) => {
const prev = a[i - 1];
const last_num = prev && prev[prev.length - 1] || 0;
a.push(ranged_array(last_num + 1, last_num + v));
return a;
}, [])
.map((v) => v.join(' '))
.join("\n");
console.log(pyramid(5));

How print an X constructed from the letter X and uses the underscore as a space in TypeScript

So heres the problem:
Write a program using TypeScript that prints an X constructed from the letter X and uses the underscore as a space. The size of the x is based on a variable n that will indicate the size of the letter to print (in a matrix of n x n). For example, for n: = 5 you get:
X___X_
_X_X_
__X__
_X_X_
X___X
and for n: = 6 we obtain:
X____X_
_X__X_
__XX__
__XX__
_X__X_
X____X
this is my code:
var n = 5;
var space = "";
for(var i = 2; i < n; i++){
space = space + "_";
for(var k = 1; k < i * 1; k++){
space = space + "X";
}
console.log(space);
}
And the ouput is:
_X
_X_XX
_X_XX_XXX

Check if the index of the outer loop is equal to the index of the inner loop, OR if the index of the outer loop is equal to (the index of the inner loop minus the line length) to decide on whether a square should have an X or not:
const makeX = n => {
for (let i = 0; i < n; i++) {
let line = '';
for (let j = 0; j < n; j++) {
line += i === j || j === (n - i - 1) ? 'X' : '_';
}
console.log(line);
}
};
makeX(5);
console.log('');
makeX(6);

let x = 5;
for(let i=0; i<x; i++) {
let str = "";
for(let k=0; k<x; k++) {
if(k==i || k==x-1-i) {
str+='X'
}
else {
str+='_'
}
if(k==x-1) {
console.log(str)
}
}
}

const X = n => new Array(n).fill(n).forEach(
(_,j,a) => console.log(a.map(
(_,i) => i == j || i == (n-j-1) ? 'X' : '_'
).join(''))
);

NaN out of matrix multiplication?

I have the code below for matrix formation out of an array and its multiplication.
But when I try to multiply two matrices like mtp(matrix(2,2,[1,2,3,4]),matrix(2,2,[1,0,0,1])) it returns NaN in all places.
Please help me out
function matrix(m, n, arr) {
var result = {};
for (t = 1; t <= m; t++) {
result[t] = {};
};
for (i = 1; i <= m; i++)
for (j = 1; j <= n; j++) result[i][j] = arr[m * (i - 1) + j - 1];
return {
"result": result,
"m": m,
"n": n
};
}
function mtp(a, b) {
if (parseInt(a.n) != parseInt(b.m)) {
return;
} else {
var result = [];
var m = parseInt(a.m);
var n = parseInt(b.n);
var k = parseInt(a.n);
for (i = 1; i <= m; i++) {
for (j = 1; j <= n; j++) {
for (p = 1; p <= k; p++) {
result[m * (i - 1) + j - 1] += (parseInt(a.result[i][p]) * parseInt(b.result[p][j]));
console.log(parseInt(a.result[i][p]) * parseInt(b.result[p][j]))
}
}
}
}
console.log(result, matrix(m, n, result).result);
}
mtp(matrix(2,2,[1,2,3,4]),matrix(2,2,[1,0,0,1]));

When you define result it is an array of zero elements
var result = [];
When you try to add a number to an element of the array, that element is not defined, Adding any number to undefined gives you NaN. There are 2 ways to solve this, either initialize your array with the right length of zeros, or default it to zero during the sum. I've chosen the latter below,
result[m * (i - 1) + j - 1] = (result[m * (i - 1) + j - 1]||0) + (a.result[i][p] * b.result[p][j]);
// Note here ---------------------------------------------^
I've got rid of all the unnecessary parseInt calls.
function matrix(m, n, arr) {
var result = {};
for (t = 1; t <= m; t++) {
result[t] = {};
};
for (i = 1; i <= m; i++)
for (j = 1; j <= n; j++) result[i][j] = arr[m * (i - 1) + j - 1];
return {
"result": result,
"m": m,
"n": n
};
}
function mtp(a, b) {
if (a.n != b.m) {
return;
} else {
var result = [];
var m = a.m;
var n = b.n;
var k = a.n;
for (i = 1; i <= m; i++) {
for (j = 1; j <= n; j++) {
for (p = 1; p <= k; p++) {
result[m * (i - 1) + j - 1] = (result[m * (i - 1) + j - 1]||0) + (a.result[i][p] * b.result[p][j]);
console.log(a.result[i][p] * b.result[p][j])
}
}
}
}
console.log(result, matrix(m, n, result).result);
}
mtp(matrix(2,2,[1,2,3,4]),matrix(2,2,[1,0,0,1]));

In your mtp() function the values of the elements inside your result array are uninitialized (that is, you've defined an array, but that array has no actual values or even a determined length), so in your inner loop when you +=, you're referencing a newly created array element which has no default value (and therefore is undefined), and adding some number to that undefined value.
An undefined value plus a number is not a number (NaN). Try preinitializing your result array.

loop three digit numbers where product == sum

So I have this task where I have to nest three loops together then find out all the three digit numbers where product == sum.
For example:
123
1*2*3 = 6
1+2+3 = 6
This is what I have tried so far:
var summen = a + b + c;
var produktet = a * b * c;
for (var i = 100; i <= 100; i++) {
for (var j = 100; j <= 101; j++) {
for (var e = 100; e < 1000; e++) {
if (summen == produktet) {
pOutput.innerHTML += e + " ";
}
}
}
Thank you in advance and any help is really appreciated!
(i thought that i need to use if and else but i'm basically stuck to be honest)

If you want to do it with three loops, use three that start at 0 and end at 9, and then add and multiply in the inner loop:
let output = [];
for (let a = 0; a < 10; a++) {
for (let b = 0; b < 10; b++) {
for (let c = 0; c < 10; c++) {
if (a * b * c === a + b + c) output.push("" + a + b + c)
}
}
}
console.log(output)

You could iterate from zero to 999 and take the stringed value as array. Then check the sum against the product and store the value if equal.
const
sum = array => array.reduce((a, b) => a + b),
product = array => array.reduce((a, b) => a * b);
var i,
temp,
values = [];
for (i = 0; i < 1000; i++) {
temp = Array.from(i.toString().padStart(3, '0'), Number);
if (sum(temp) === product(temp)) {
values.push(temp.join(''));
}
}
console.log(values);