How to make many variables in Javascript

Question

everyone! I am pretty new at Javascript and I wanted to challenge myself by making a program that will figure out if the number entered is prime. So far, this is my code:

var a = prompt('What should the number be?');
var n = parseInt(a);           
var counter = n - 1;
var b = n/counter;
var c = Math.floor(b);
if (n < 1) {
            window.alert('Invalid: negative numbers are neither prime nor composite!');
        }
        if (n === 1){
            window.alert('1 is neither prime nor composite!');
        } else {
            if (b-c != 0) {

            }
        }

I am planning to make a bunch of variables, each with a name that differs by a number. I do not need an easier or different way to write my code. So how do I make the script write many different variable automatically? Thanks in advance!

Surreal Dreams · Accepted Answer · 2013-06-20 15:04:38Z

5

This sounds like a good case for using an array. It's an easy way to store lots of values in the same variable name, but called by an index - a number. Check out the MDN page for arrays.

Here's an example of stashing lots of values in an array:

var bigNumber = 100000;
var myArray = new Array();
var tally = 0;
for( i = 0; i < bigNumber; i++ )
{
    tally += i;
    myArray[i] = tally;
}

When this is done, myArray will have 100000 values in it. myArray[0] = 0, myArray[1] = 1, myArray[2] = 3, myArray[3] = 6, myArray[4] = 10, etc.

edited Jun 20, 2013 at 15:04

answered Jun 20, 2013 at 14:47

Surreal Dreams

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5 Comments

Surreal Dreams Over a year ago

I'm old school - I always forget about that. I wanted to ensure that there were predictable numerical indexes on the values, since the original question included that idea.

justinpchang Over a year ago

how do i turn the array into a variable though

Surreal Dreams Over a year ago

An array is a collection of variables. Re-read the end of my answer, it shows how to access the individual values stored in the array.

justinpchang Over a year ago

how do i make the program automatically access the values of the array

Surreal Dreams Over a year ago

Read up on loops - I used one to set the values in my example. You can also use one to use all the values in the array.

inf3rno · Accepted Answer · 2013-06-20 15:10:22Z

I don't think your problems is with too many variables. You should use functions to separate code parts with different purpose:

function isPrime(n) {
    var counter = n - 1;
    var b = n / counter;
    var c = Math.floor(b);
    if (n < 1) {
        return false;
    }
    if (n === 1) {
        return false;
    } else {
        if (b - c != 0) {

        }
    }
}


var n = parseInt(prompt('What should the number be?'));
alert('The given number ' + n + ' is ' + (isPrime(n) ? '' : ' not') + ' a prime.');

or

function PrimeChecker(){
    var n = this.readNumber();
    this.displayResult(n, this.isPrime(n));
}
PrimeChecker.prototype = {
    readNumber: function (){
        return parseInt(prompt('What should the number be?'));
    },
    isPrime: function (n) {
        var counter = n - 1;
        var b = n / counter;
        var c = Math.floor(b);
        if (n < 1) {
            return false;
        }
        if (n === 1) {
            return false;
        } else {
            if (b - c != 0) {

            }
        }
    },
    displayResult: function (n, isPrime){
        alert('The given number ' + n + ' is ' + (isPrime ? '' : ' not') + ' a prime.');
    }
};

new PrimeChecker();

If you want to group variables you can still use an object to store them:

var map = {
    a: 1,
    b: 2,
    c: 3
};
map.d = 4;
map.e = 5;
alert(map.e);

If you generate variables without name, you can use an array:

var array= [
    "a",
    "b",
    "c"
];
array.push("d");
array.push("e");
alert(array[4]);

Stephen Sorensen · Accepted Answer · 2013-06-20 14:47:53Z

0

The evil way to do it would be to create variables on the global object (window), like so:

// This is bad because it pollutes the global namespace:
for (var i = 0; i < 10; i++) {
  window['num' + i] = i;
}

A better way would be to create an empty object and use that as a namespace for your variables.

var o = {};
for (var i = 0; i < 10; i++) {
  o['num' + i] = i;
}

answered Jun 20, 2013 at 14:47

Stephen Sorensen

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