We Keep Coding

Digital Root (repeated digital sum) code issue

Question : Given n, take the sum of the digits of n. If that value has
more than one digit, continue reducing in this way until a
single-digit number is produced. The input will be a non-negative
integer. Ex- 16 --> 1 + 6 = 7 942 --> 9 + 4 + 2 = 15 --> 1 +
5 = 6 132189 --> 1 + 3 + 2 + 1 + 8 + 9 = 24 --> 2 + 4 = 6 493193
--> 4 + 9 + 3 + 1 + 9 + 3 = 29 --> 2 + 9 = 11 --> 1 + 1 = 2
function digitalroot(n) {
let a = n;
var sum = 0;
while(a >= 1){
sum += a % 10;
a = Math.trunc(a/10)
}
if(sum > 9){
digitalroot(sum)
}
console.log("Print")
console.log(sum)
return sum
}
I tried above code but not getting correct output with below called input
With this two inputs passed in function: (16), (456)
O/P:
Print
7
Print
6
Print
15
Please help me, I am new to JavaScript

you forgot to return value from function call inside that sum>9 condition.
check recursion here : w3School
function digitalroot(n) {
let a = n;
var sum = 0;
while(a >= 1){
sum += a % 10;
a = Math.trunc(a/10)
}
if(sum > 9){
return digitalroot(sum)
}
return sum
}
console.log(digitalroot(493193));

Check this working example
function digitalroot(n){
console.log(`Value of n = ${n}`)
var digits = (""+n).split("");
for (var i = 0; i < digits.length; i++) {
digits[i] = +digits[i];
}
var finalVal = digits
let result = finalVal.reduce((a, b) => a + b, 0)
console.log(`Final Value with list ${result}`)
}
digitalroot(289)

How to return data from a function

I'm trying to solve the following Kata:
a 2 digit number, if you add the digits together, multiply by 3, add 45 and reverse.
I'm unable to figure out how to return the data from my function so that I can later assign the value to an HTML element.
This is my code.
function daily() {
for(var j = 10; j < 100; j++) {
function teaser(num) {
var x = num;
var y = x.toString().split("");
if(y.length == 2) {
var sum = parseInt(y[0]) + parseInt(y[1]);
if(sum * 3 == x) {
console.log(x + " is equal to 3 times " + sum);
var addFortyFive = x + 45;
console.log("Adding 45 to " + x + " gives " + addFortyFive);
var reversal = parseInt(addFortyFive.toString().split('').reverse().join(''));
console.log("'The 2 digit number " + x + ", is 3 times the sum (" + sum + ") of its digits. If 45 is added to " + x + ", the result is " + addFortyFive + ". If the digits are reversed, the number is... " + reversal + ".");
}
} else {
console.log("Not a 2 digit Number!!");
}
}
teaser(j);
}
}

From your question I'm guessing you need reversal value on function daily for loop.
Would recommend you to take out function teaser from inside for-loop, this will make code much cleaner and easy to understand and you can do like:
function daily() {
for(var j = 10; j < 100; j++) {
var teaser = teaser(j);
// Can now use anything returned from teaser function here
}
}
function teaser(num) {
var x = num;
var y = x.toString().split("");
if(y.length == 2) {
var sum = parseInt(y[0]) + parseInt(y[1]);
if(sum * 3 == x) {
console.log(x + " is equal to 3 times " + sum);
var addFortyFive = x + 45;
console.log("Adding 45 to " + x + " gives " + addFortyFive);
var reversal = parseInt(addFortyFive.toString().split('').reverse().join(''));
console.log("'The 2 digit number " + x + ", is 3 times the sum (" + sum + ") of its digits. If 45 is added to " + x + ", the result is " + addFortyFive + ". If the digits are reversed, the number is... " + reversal + ".");
return reversal;
}
} else {
console.log("Not a 2 digit Number!!");
return false;
}
}
If don't want to take function out then you can do this:
function daily() {
for(var j = 10; j < 100; j++) {
function teaser(num) {
var x = num;
var y = x.toString().split("");
if(y.length == 2) {
var sum = parseInt(y[0]) + parseInt(y[1]);
if(sum * 3 == x) {
console.log(x + " is equal to 3 times " + sum);
var addFortyFive = x + 45;
console.log("Adding 45 to " + x + " gives " + addFortyFive);
var reversal = parseInt(addFortyFive.toString().split('').reverse().join(''));
console.log("'The 2 digit number " + x + ", is 3 times the sum (" + sum + ") of its digits. If 45 is added to " + x + ", the result is " + addFortyFive + ". If the digits are reversed, the number is... " + reversal + ".");
return reversal;
}
} else {
console.log("Not a 2 digit Number!!");
return false;
}
}
var teaser = teaser(j);
// Can now use anything returned from teaser function here
}
}

Returning something from a function is very simple!
Just add the return statement to your function.
function sayHello(name) {
return 'Hello ' + name + '!';
}
console.log(sayHello('David'));

okay, so my issue has been solved! Thanks all of you, especially krillgar, so I had to alter the code you gave me krillgar, a little bit in order to populate the results array with only the numbers (one number in this case) that satisfy the parameters of the daily tease I was asking about. yours was populating with 89 undefined and on number, 27 because it is the only number that works.
One of my problems was that I was expecting the return statement to not only save a value, but also show it on the screen, but what I was not realizing was that I needed a place to store the value. In your code you created a result array to populate with the correct numbers. And also, I needed a variable to store the data for each iteration of the for loop cycling through 10 - 100. Anyways, you gave me what I needed to figure this out and make it do what I wanted it to do, and all is well in the world again.
Anyway, thank you all for your help and input, and I will always remember to make sure I have somewhere to store the answers, and also somewheres to store the value of each loop iteration in order to decide which numbers to push into the results array and save it so it can be displayed and/or manipulated for whatever purpose it may be. I guess I was just so busy thinking about the fact that when I returned num it didn't show the value, instead of thinking about the fact that I needed to store the value. Here is the final code for this problem and thanks again peoples!
function daily() {
var results = [];
for(var j = 10; j < 100; j++) {
function teaser(num) {
var x = num;
var y = x.toString().split("");
if(y.length == 2) {
var sum = parseInt(y[0]) + parseInt(y[1]);
if(sum * 3 == x) {
console.log(x + " is equal to 3 times " + sum);
var addFortyFive = x + 45;
console.log("Adding 45 to " + x + " gives " + addFortyFive);
var reversal = parseInt(addFortyFive.toString().split('').reverse().join(''));
console.log("'The 2 digit number " + x + ", is 3 times the sum (" + sum + ") of its digits. If 45 is added to " + x + ", the result is " + addFortyFive + ". If the digits are reversed, the number is... " + reversal + ".");
return num;
// Here you have one that is correct, so return it:
} else {
console.log(num + " does not fulfill function parameters");
// This is just so you can visualize the numbers
return null;
}
}
}
var answer = teaser(j);
if(answer != null) {
results.push(answer);
}
}
return results;
}

As was said in the comments of the question, because you're going to (most likely) have multiple answers that match your condition, you will need to store those in an array. Your teaser function returns individual results, where daily will check all the numbers in your range.
function daily() {
var results = [];
for(var j = 10; j < 100; j++) {
function teaser(num) {
var x = num;
var y = x.toString().split("");
if(y.length == 2) {
var sum = parseInt(y[0]) + parseInt(y[1]);
if(sum * 3 == x) {
console.log(x + " is equal to 3 times " + sum);
var addFortyFive = x + 45;
console.log("Adding 45 to " + x + " gives " + addFortyFive);
var reversal = parseInt(addFortyFive.toString().split('').reverse().join(''));
console.log("'The 2 digit number " + x + ", is 3 times the sum (" + sum + ") of its digits. If 45 is added to " + x + ", the result is " + addFortyFive + ". If the digits are reversed, the number is... " + reversal + ".");
// Here you have one that is correct, so return it:
return num;
} else {
// Make sure we don't return undefined for when the sum
// times three doesn't equal the number.
return null;
}
} else {
console.log("Not a 2 digit Number!!");
return null;
}
}
var answer = teaser(j);
if (answer !== null) {
results.push(answer);
}
}
return results;
}

How to return a String representation of a calculation in Javascript

I am currently trying to complete an assignment for an intro2Javascript course. The question basically asks me to return a string of multiples of 2 parameters (num, numMultiple). Each time it increments the value i until i = numMultiple. For example:
5 x 1 = 5\n
5 x 2 = 10\n
5 x 3 = 15\n
5 x 4 = 20\n
This was my attempt:
function showMultiples(num, numMultiples) {
var result;
for (i = 1; i <= numMultiples; i++) {
result = num * i
multiples = "" + num + " x " + i + " = " + result + "\n"
return (multiples)
}
}
...and because the assignment comes with pre-written console logs:
console.log('showMultiples(2,8) returns: ' + showMultiples(2, 8));
console.log('showMultiples(3,2) returns: ' + showMultiples(3, 2));
console.log('showMultiples(5,4) returns: ' + showMultiples(5, 4));
console.log('\n');
This is my output:
showMultiples(2,8) returns: 2 x 1 = 2
Scratchpad/1:59:1
showMultiples(3,2) returns: 3 x 1 = 3
Scratchpad/1:60:1
showMultiples(5,4) returns: 5 x 1 = 5
UPDATE

You were doing two things incorrectly:
1) You were returning after the first iteration through your loop
2) You were assigning to multiples instead of appending to it.
Since you want to gather all the values and then show the final result first, I add all of the values to an array, and then use unshift() to add the final element (the result) to the beginning of the array. Then I use join() to return a string representation of the desired array.
function showMultiples(num, numMultiples) {
var result;
var multiples = [];
for (let i = 1; i <= numMultiples; i++) {
result = num * i
multiples.push("" + num + " x " + i + " = " + result + "\n")
}
multiples.unshift(multiples[multiples.length-1]);
return (multiples.join(''))
}
console.log('showMultiples(2,8) returns: ' + showMultiples(2, 8));
console.log('showMultiples(3,2) returns: ' + showMultiples(3, 2));
console.log('showMultiples(5,4) returns: ' + showMultiples(5, 4));
console.log('\n');

You need to declare all variables, because without you get global variables (beside that it does not work in 'strict mode').
The second point is to use multiples with an empty string for collecting all intermediate results and return that value at the end of the function.
For keeping the last result, you could use another variable and append that value at the end for return.
function showMultiples(num, numMultiples) {
var i,
result,
multiples = "",
temp = '';
for (i = 1; i <= numMultiples; i++) {
result = num * i;
temp = num + " x " + i + " = " + result + "\n";
multiples += temp;
}
return temp + multiples;
}
console.log('showMultiples(2,8) returns: ' + showMultiples(2, 8));
console.log('showMultiples(3,2) returns: ' + showMultiples(3, 2));
console.log('showMultiples(5,4) returns: ' + showMultiples(5, 4));

As other answers say, your problem is in multiple.
You are clearing multiple every iteration and storing the new value, but you do not want that, you want to add the new result, and to do so you use this code:
multiples = multiple + "" + num + " x " + i + " = " + result + "\n"
which can be compressed in what the rest of the people answered:
multiples += "" + num + " x " + i + " = " + result + "\n"
Probably you already know, but to ensure:
a += b ---> a = a + b
a -= b ---> a = a - b
a *= b ---> a = a * b
and there are even more.

How to combine these specific Javascript statements?

1.I include what the two lines i want to combine in the first comment of the code. If you can point me to what i need to do it would really help. I just started javascript a couple days ago. If u can recommend any books please tell me. im currently reading the murach series of books and its really helping.
/*The two statements i want to combine are
entry = parseInt(entry);
var score1 = entry; */
<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
<title>Average Test Scores</title>
<script>
var entry;
var average;
var total = 0;
//get 3 scores from user and add them together
entry = prompt("Enter test score");
entry = parseInt(entry);
var score1 = entry;
total = total + score1;
entry = prompt("Enter test score");
entry = parseInt(entry);
var score2;
total = total + score2;
entry = prompt("Enter test score");
entry = parseInt(entry);
var score3 = entry;
total = total + score3;
//calculate the average
average = parseInt(total/3);
</script>
</head>
<body>
<script>
document.write("<h1>The Test Scores App</h1>");
document.write("Score 1 = " + score1 + "<br>" +
"Score 2 = " + score2 + "<br>" +
"Score 3 = " + score3 + "<br><br>" +
"Average score = " + average + "<br><br>");
</script>
Thanks for using the Test Scores application!
</body>
</html>

Addition assignment, The addition assignment operator adds the value of the right operand to a variable and assigns the result to the variable.
Unary plus (+), The unary plus operator precedes its operand and evaluates to its operand but attempts to converts it into a number, if it isn't already.
Simplified version:
var total = 0;
var score1 = +prompt("Enter test score"); //Cast it to Number
total += score1; //Add it to total
var score2 = +prompt("Enter test score");
total += score2;
var score3 = +prompt("Enter test score");
total += score3;
var average = parseInt(total / 3);
document.write("<h1>The Test Scores App</h1>");
document.write("Score 1 = " + score1 + "<br>" +
"Score 2 = " + score2 + "<br>" +
"Score 3 = " + score3 + "<br><br>" +
"Average score = " + average + "<br><br>");

how to get the position of a number in matrix?

How can I get the number's position by c or Javascript.
It is a ordered number array,like
1 2
3 4
5 6
how can I make a function to get the number 3 is 2-1,and 6 is 3-2
Thank you very much!

You could do something like this in javascript
var data = [
[1, 2],
[3, 4],
[5, 6]
];
var getPos = function(elem, data) {
var result = '';
data.forEach(function(value, index) {
value.forEach(function(v, i) {
if (v == elem) result += (index + 1) + '-' + (i + 1);
});
});
return result;
}
console.log(getPos(5, data));

In C you could write a function that would implement the following pseudo-code:
//...
for(i=0 ; i<ARRAY_SIZE ; i++)
{
if(array[i] == desired_num)
return i;
else
i++;
}
return -1; // return error if desired_num not found
//...

If it's a continuous ordered two-dimensional array you can do something like this to get the indices. (Notice +1 as per your example)
int x = floor(number/2) +1:
int y = (number+1)%2 +1;
If you are using arrays you should be able to jump the the right index without needing to loop like I see other answers suggesting.
array[x][y]

You may do something like this
var table = (new Array (10)).fill(new Array(10).fill("")).map( e=> e.map( f => ~~(Math.random()*1000))),
results = [];
function findInTable(t, q){
var finds = {x:[],y:[]};
t.forEach( (a, i) => {j = a.indexOf(q); ~j && (finds.x.push(j+1), finds.y.push(i+1))});
return finds;
}
results = findInTable(table, 777);
document.write("<pre>" + table[0] + "\n" + table[1] + "\n" + table[2] + "\n" + table[3] + "\n" + table[4] + "\n" + table[5] + "\n" + table[6] + "\n" + table[7] + "\n" + table[8] + "\n" + table[9] + "\n" +"</pre>");
document.write("<pre> Searched for " + 777+ " and found at:\n" + JSON.stringify(results, null, 4) + "</pre>");