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Count the number of occurrences of 7 in a number given by the user

while (a) {
b.push(a % 10);
a = Math.floor(a / 10);
if (b == 7) {
n = n + 1;
}
console.log("<br><br>number of 7's:" + n);
}
This is what I have come up with. The output is one of the numbers has seven; if not, then zero. I want the program to count the number of times seven appears in a number.

You can convert the number to a string, and then count how many times a character = 7:
let n = 7326577
let cnt = 0;
let strN = '' + n;
for(let c of strN)
if(c == '7')
cnt ++
console.log('Number of 7\'s in number: ' + cnt)

Following you approach you need to store the last digit to a different variable and use that for checking if it is a 7
var a = 709728457;
var b = [];
var n = 0;
while (a) {
const lastDigit = a % 10;
b.push(lastDigit); // if you still need to store all digits
a = Math.floor(a / 10);
if (lastDigit == 7) {
n = n + 1;
}
}
console.log("number of 7's:" + n);

var a = 7686774737
var no = String(a).split('').filter(e=>e==7).length;
console.log(no)

Javascript numbers - split/slice Prime

I am completely new to Javascript and trying to solve a simple problem now for more than two weeks and still not getting it(please help).
TASK ::::
Read a 4 digit Number e.g. 5678
Write a function
Split/separate the numbers and than build (5678, 567, 56, 5), than check if the numbers(5678, 567, 56, 5) are Prime numbers.
Give in Console/Result if 5678 a prime number or not, 567 a prime number or not and so on.
Check "if all numbers are Prime" than show result "All prime" if not show result "Not all prime".
Trying to solve the problem with (if else) but not really getting it, because i know very less about Javascript (arrays, string, split, slice) yet.
please help me understand. Thanks.
var a = 123456789;
var b = a.toString().length; //<<--->> ANTWORT: 9
document.write('ANTWORT: ',a );
for (i=0; i<b; i++) {
var x = a.toString().slice(0, -i);
document.write(x, ",");
}
function isPrime{
for(var i = 2; i < a; i++);
if(num % i === 0) return false;
return num > 1;
}

//integer is a string at the moment
integer = prompt("Enter a integer: ");
//initialize array for dictionary
dictArray = [];
stuff = document.getElementById("stuff");
//loop through all values of the string
for (var i = integer.length; i > 0; i--)
{
//take a substring from 0 to the ith char and turn it into an int
num = parseInt(integer.substring(0, i));
//add a dictionary to the array the tells what the number is
//and if it was prime or not as a bool
dictArray.push({"num": num, "prime": isprime(num)});
(dictArray[integer.length - i]["prime"]) ? stuff.innerHTML += "<br>" + num + " is prime." : stuff.innerHTML += "<br>" + num + " is not prime.";
}
function isprime(num)
{
if (num <= 3) return num >= 1;
if ((num % 2 === 0) || (num % 3 === 0)) return false;
let count = 5;
while (Math.pow(count, 2) <= num) {
if (num % count === 0 || num % (count + 2) === 0) return false;
count += 6;
}
return true;
}
//print the array
(dictArray.find(x => !x.prime) == undefined) ? stuff.innerHTML += "<br>All prime!" : stuff.innerHTML += "<br>Not all prime!";
//console.log(dictArray);
<div id="stuff">
</div>

Sorting an integer without using string methods and without using arrays

can anyone come with an idea of how to sort an integer without using an array, and without using string methods as well as sort() method?
for example
input: 642531
output: 123456
I started by writing 2 simple functions - one which checks the length of the number, the other one splits the integer at some point and switches between 2 desired numbers. Below are the 2 functions.
I got stuck with the rest of the solution...
function switchDigits(num, i) { // for input: num=642531, i = 4 returns 624135
let temp = num;
let rest = 0;
for (let j = 0; j < i - 1; j++) {
rest = rest * 10;
rest = rest + temp % 10;
temp = (temp - temp % 10) / 10;
}
let a = temp % 10;
temp = (temp - a) / 10;
let b = temp % 10;
temp = (temp - b) / 10;
temp = Math.pow(10, i - 2) * temp;
temp = temp + 10 * a + b;
temp = Math.pow(10, i - 1) * temp;
temp = temp + rest;
return temp;
}
function checkHowManyDigits(num) { //input: 642534, output: 6 (length of the integer)
let count = 0;
while (num > 0) {
let a = num % 10;
num = (num - a) / 10;
count++;
}
return count;
}
let num = 642534;
let i = checkHowManyDigits(num);
console.log(switchDigits(num));

It actually complicated requirement and so does this answer. It's pure logic and as it is it's a question from a test you should try understanding the logic on your own as a homework.
function checkHowManyDigits(num) { //input: 642534, output: 6 (length of the integer)
let count = 0;
while (num > 0) {
let a = num % 10;
num = (num - a) / 10;
count++;
}
return count;
}
function sortDigit(numOriginal) {
let i = checkHowManyDigits(numOriginal);
let minCount = 0;
let min = 10;
let num = numOriginal;
while (num > 0) {
let d = num % 10;
num = (num - d) / 10;
if (d < min) {
min = d;
minCount = 0;
} else if (d === min) {
minCount++;
}
}
let result = 0;
while (minCount >= 0) {
result += min * Math.pow(10, i - minCount - 1);
minCount--;
}
let newNum = 0;
num = numOriginal;
while (num > 0) {
let d = num % 10;
num = (num - d) / 10;
if (d !== min) {
newNum = newNum * 10 + d;
}
}
if (newNum == 0) return result;
else return result += sortDigit(newNum);
}
console.log(sortDigit(642531));

You could have a look to greater and smaller pairs, like
64
46
The delta is 18, which gets an idea if you compare other pairs, like
71
17
where the delta is 54. Basically any difference of two digits is a multiple of 9.
This in mind, you get a function for taking a single digit out of a number and a single loop who is sorting the digits by using the calculated delta and subtract the value, adjusted by the place.
function sort(number) {
const
getDigit = e => Math.floor(number / 10 ** e) % 10,
l = Math.ceil(Math.log10(number)) - 1;
let e = l;
while (e--) {
const
left = getDigit(e + 1),
right = getDigit(e);
if (left <= right) continue;
number += (right - left) * 9 * 10 ** e;
e = l;
}
return number;
}
console.log(sort(17)); // 17
console.log(sort(71)); // 17
console.log(sort(642531)); // 123456
console.log(sort(987123654)); // 123456789

So eventually I found the best solution.
*This solution is based on a Java solution I found in StackOverFlow forums.
let store = 0;
function getReducedNumbr(number, digit) {
console.log("Remove " + digit + " from " + number);
let newNumber = 0;
let repeateFlag = false;
while (number>0) {
let t = number % 10;
if (t !== digit) {
newNumber = (newNumber * 10) + t;
} else if (t == digit) {
if (repeateFlag) {
console.log(("Repeated min digit " + t + " found. Store is : " + store));
store = (store * 10) + t;
console.log("Repeated min digit " + t + " added to store. Updated store is : " + store);
} else {
repeateFlag = true;
}
}
number = Math.floor(number / 10);
}
console.log("Reduced number is : " + newNumber);
return newNumber;}
function sortNum(num) {
let number = num;
let original = number;
let digit;
while (number > 0) {
digit = number % 10;
console.log("Last digit is : " + digit + " of number : " + number);
temp = Math.floor(number/10);
while (temp > 0) {
console.log("subchunk is " + temp);
t = temp % 10;
if (t < digit) {
digit = t;
}
temp = Math.floor(temp/10);
}
console.log("Smallest digit in " + number + " is " + digit);
store = (store * 10) + digit;
console.log("store is : " + store);
number = getReducedNumbr(number, digit);
}
console.log(("Ascending order of " + original + " is " + store));
return store;
}
console.log(sortNum(4214173));
you can see how it works here https://jsfiddle.net/9dpm14fL/1/

Convert from one base to another in JavaScript [duplicate]

This question already has answers here:
How do you convert numbers between different bases in JavaScript?
(21 answers)
Closed 1 year ago.
In JavaScript, is there any built-in function for converting an integer from one given base to another given base? I've noticed that it's already possible to convert a decimal number to another base using toString(numberToConvertTo), but I haven't yet found a general-purpose function that can convert from any base to any other base, as shown:
convertFrom(toConvert, baseToConvertFrom, baseToConvertTo){
//convert the number from baseToConvertFrom to BaseToConvertTo
}

Call parseInt(str, fromBase) to convert to base 10 (or rather, to an actual number), then call num.toString(toBase).

You might want to customise your input or output. You might want more than 36 bases. So I made this
function baseCon(number,fromBase,toBase,fromChars,toChars) {
if (!fromChars) {
fromChars = ['0','1','2','3','4','5','6','7','8','9','A','B','C','D','E','F','G','H','I','J','K','L','M','N','O','P','Q','R','S','T','U','V','W','X','Y','Z'];
number = number.toString().toUpperCase();
}
if (!toChars) {
toChars = ['0','1','2','3','4','5','6','7','8','9','A','B','C','D','E','F','G','H','I','J','K','L','M','N','O','P','Q','R','S','T','U','V','W','X','Y','Z'];
}
if (typeof number != 'object') {
number = number.toString();
}
if (fromBase > fromChars.length) {
console.log('fromBase was too high');
} else if (toBase > toChars.length) {
console.log('toBase was too high');
} else {
if (fromBase == 10) {
var base10Num = Math.min(number);
} else {
var base10Num = 0;
var place = 0;
for (var index = number.length - 1; index > -1; index--) {
base10Num = base10Num + (fromChars.indexOf(number[index]) * Math.pow(fromBase,place));
place++;
}
}
var string = '';
var looping = true;
var stringLen = 0;
var stringVal = 0;
while (looping) {
stringLen++;
if (Math.pow(toBase,stringLen) == base10Num) {
stringLen++;
break;
} else if (Math.pow(toBase,stringLen) >= base10Num) {
break;
}
}
for (var placePos = stringLen; placePos > 0; placePos--) {
for (var placeVal = 0; placeVal < (toBase + 1); placeVal++) {
if (((placeVal * Math.pow(toBase,placePos - 1)) > (base10Num - stringVal)) || (placeVal == 0) && ((base10Num - stringVal) == 0)) {
if (!((placeVal == 0) && ((base10Num - stringVal) == 0))) {
stringVal = stringVal + ((placeVal - 1) * Math.pow(toBase,placePos - 1));
string = string + toChars[placeVal - 1];
} else {
string = string + toChars[0];
}
break;
}
}
}
if (stringVal == base10Num) {
return string;
} else {
console.log('baseCon failed');
return string;
}
}
};
You can customise the input chars so you can do things like this
> baseCon([true,true,false,true,false],2,10,[false,true]);
< "26"
and of coarse the output chars
> baseCon('3942',10,8,false,['!','#','#','$','%','^','&','*']);
< "*^%&"
It took me all day and then I remembered parseInt(number,fromBase).toString(toBase); haha

Convert integer to alpha ordered list equivalent

I need to a function to convert an integer to the equivalent alpha ordered list index. For example:
1 = a
2 = b
.
.
.
26 = z
27 = aa
28 = ab
.
.
etc.
Currently I have the following which almost works but there's a small logic error somewhere that makes it not quite get it right (it goes ax, ay, bz, ba, bb, bc...):
function intToAlpha( int ) {
var asciiStart = 97,
alphaMax = 26,
asciiCode,
char,
alpha = '',
place,
num,
i;
for ( i = 0; Math.pow(alphaMax, i) < int; i++ ) {
place = Math.pow(alphaMax, i);
num = Math.floor( ( int / place ) % alphaMax);
asciiCode = ( num == 0 ? alphaMax : num ) + asciiStart - 1;
char = String.fromCharCode(asciiCode);
alpha = char + alpha;
}
return alpha;
}
for (i = 1; i < 300; i++) {
console.log( i + ': ' + intToAlpha(i) );
}

This function is used in NVu/Kompozer/SeaMonkey Composer, with a small tweak to generate lower case directly:
function ConvertArabicToLetters(num)
{
var letters = "";
while (num > 0) {
num--;
letters = String.fromCharCode(97 + (num % 26)) + letters;
num = Math.floor(num / 26);
}
return letters;
}

You need to make sure that you use the correct value when taking the mod.
function intToAlpha( int ) {
var asciiStart = 97,
alphaMax = 26,
asciiCode,
char,
alpha = "";
while(int > 0) {
char = String.fromCharCode(asciiStart + ((int-1) % alphaMax));
alpha = char + alpha;
int = Math.floor((int-1)/26);
}
return alpha;
}

A while back I needed the same thing in SQL, so I asked (and answered) the question Multi-base conversion - using all combinations for URL shortener.
The thing that is making it complicated is that it's not a straight base conversion, as there is no character representing the zero digit.
I converted the SQL function into Javascript:
function tinyEncode(id) {
var code, value, adder;
var chars = 'abcdefghijklmnopqrstuvwxyz';
if (id <= chars.length) {
code = chars.substr(id - 1, 1);
} else {
id--;
value = chars.length;
adder = 0;
while (id >= value * (chars.length + 1) + adder) {
adder += value;
value *= chars.length;
}
code = chars.substr(Math.floor((id - adder) / value) - 1, 1);
id = (id - adder) % value;
while (value > 1) {
value = Math.floor(value / chars.length);
code += chars.substr(Math.floor(id / value), 1);
id = id % value;
}
}
return code;
}
Demo: http://jsfiddle.net/Guffa/mstBe/