array

The sieve of Eratosthenes is named after Eratosthenes of Cyrene who was a Greek mathematician who devised a mechanism to find a sequence of prime numbers using a simple algorithm.

Normally, looping through a list of numbers and finding the primes can be an expensive process. The seive of Eratosthenes is one of the most efficient way of working out all of the smaller prime numbers below (below 10 million or so).

It is usual when writing a list of items to separate each item with a comma, except the last two items, which are separated with the word "and". I recently needed to implement a function that took a string and converted it into a list of this type so I thought I would expand on it and post it here.

I have previously talked about Removing commas from the end of strings, but it is also possible to use the implode() function to do the same sort of thing.

implode() takes two parameters, the separator and the array, and returns a string with each array item separated with the separator. The following example shows how this function works.

Use the following array to print out a list of Canadian states, also know as provinces.

Use the following array if you want to print out a list of USA states either as a list, or as a select box.

In any office there can be arguments about who will make the next round of tea. The following script will allow you to randomly pick a person who is going to make the tea. Rather than have a script that did this once and threw away the information I thought it would be a good idea to use cookies to save the form data for the next time you want to pick a person to make the tea. This is a good exercise if you are trying to understand how cookies work.

First, we will need to variables, the first is an array of people and the second is the number of people in the office.

If you are familiar with PHP you will have come across the for loop at some point. When learning JavaScript it is important to remember that it also has the ability to do the equivalent of the PHP forloop.

The following snippet shows the creation of an array of things that can't be referenced by a normal for loop due to the odd numbering of the keys.

Use the following code to create an array of counties in the UK.

I have talked about swapping values without a temporary third variable before, but there is another way to do this which doesn't make the code unreadable. This is by using the list() function in the following way.