## JavaScript program to find if a number is a Magic number or not:

In this post, we will learn how to find if a number is a *Magic number* or not with JavaScript. We will write a program that will take one number as input from the user, check if it is a *Magic number* and print out the result.

### What is a Magic number:

A number is called a *Magic number* if the repeated sum of digits of that number is equal to *1*. *9721* is a Magic number. Let me show you how:

- The sum of digits of
*9721*is*9 + 7 + 2 + 1*or*19*. - Since
*19*is a two digit number, we have to find the sum of digits of*19*which is*10*. Similarly, the sum of digits of*10*is*1*. Hence, the repeated sum of digits of the number is equal to*1*and so*9721*is a Magic number.

Similarly, *2179, 10* etc. are Magic numbers.

We will have to find the repeated sum of digits of a number first and if we compare it with *1*, we can find if a number is a Magic number or not.

### Example 1: Magic number program with a while loop:

The following program uses a *while loop* to check if a number is *Magic number* or not:

```
let no = 9721;
let copyNo = no;
let sum = no;
while(copyNo > 9){
sum = 0;
while(copyNo > 0){
sum += copyNo%10;
copyNo = parseInt(copyNo/10);
}
copyNo = sum;
}
if(sum == 1){
console.log(`${no} is a Magic number`)
}else{
console.log(`${no} is not a Magic number`)
}
```

In this program,

- The variable
*no*holds the given number. We created a copy of the number,*copyNo*. The program works on this copied number. It also initialized another*sum*variable to hold the repeated sum. - There are two
*while loops*used in the program.- The outer loop runs until the value of
*copyNo*is greater than*9*. Inside this loop, it finds the sum of digits of the number and assigns that sum to*copyNo*. So, at the end of this loop, the*sum*variable will hold the repeated sum of digits of the number. - The inner loop finds the sum of digits of the number
*copyNo*. It finds the last digit of the number, adds it to the*sum*variable and removes it from*copyNo*.

- The outer loop runs until the value of
- Once the loop ends, we can compare the value of the
*sum*variable with*1*. If it is equal to*1*, it is a*Magic number*. Else, it is not a Magic number.

You can try this program with different numbers to check for Magic numbers.

### Example 2: Magic number program with HTML, JS:

We can also write this program with *HTML* and *JavaScript*. Create one *index.html* file with the below content:

```
<!DOCTYPE html>
<html lang="en">
<head>
<script>
function checkMagic() {
let no = document.getElementById("no").value;
let copyNo = no;
let sum = no;
while (copyNo > 9) {
sum = 0;
while (copyNo > 0) {
sum += copyNo % 10;
copyNo = parseInt(copyNo / 10);
}
copyNo = sum;
}
if (sum == 1) {
document.getElementById("result").innerText = `${no} is a Magic number`;
} else {
document.getElementById("result").innerText = `${no} is not a Magic number`;
}
}
</script>
</head>
<body>
<input type="text" id="no" placeholder="Enter the number" />
<button onclick="checkMagic()">Check</button>
<text id="result"></text>
</body>
</html>
```

You can open this file in any web browser to check the result.

- It has one
*input*field to take the number input. The user will enter the number in that field. - One button is there. On clicking the button, it will call the
*checkMagic*function.- The
*checkMagic*function checks if the entered number is a Magic number or not. - It updates the result in the
*text*field.

- The

It will give result as below:

### Example 3: Find all Magic numbers in a range in JavaScript:

Let’s change the above program to find all Magic numbers in a range with JavaScript.

```
function isMagic(no) {
let copyNo = no;
let sum = no;
while (copyNo > 9) {
sum = 0;
while (copyNo > 0) {
sum += copyNo % 10;
copyNo = parseInt(copyNo / 10);
}
copyNo = sum;
}
return sum == 1;
}
console.log(`Magic numbers between 1 and 100 are: `);
for(let i = 1; i <= 100; i++){
if(isMagic(i)){
console.log(i);
}
}
```

We moved the code to a new function *isMagic*. This function takes one number as its parameter and returns one boolean value. It is finding all magic numbers in between *1* and *100* by using a *for loop*. The loop runs from *1* to *100* and on each iteration, it checks if the current value is a Magic number or not. If yes, it prints that value.

It prints the below output:

```
Magic numbers between 1 and 100 are:
1
10
19
28
37
46
55
64
73
82
91
100
```

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