Arrays

Create an array

An array is a fixed length set of elements. There are two ways to create an array: either by specifing each element, semicolon separated, between [| and |], or by repeting an element a fixed number of times.

let array1 = [|1; 2; 3; 4|];;
let array2 = Array.make 3 0;; (* [|0; 0; 0|] *)

Array length

You can get the length of an array using the Array.length method:

let array1 = [|1; 2; 3; 4|];;
let len = Array.length array1;; (* len = 4 *)

Get an element from an array

You can get elements from an array using its index. The first element’s index is 0, and the last one’s index is n-1, for an array of length n.

let array1 = [|1; 2; 3; 4|] in
print_int array1.(2);; (* 3 *)

Using a for loop, you can iterate elements of an array like in this example:

let array1 = [|1; 2; 3; 4|] in
let len = Array.length array1 in
for k = 0 to len-1 do
print_int array1.(k)
done;;

In this example, k will be incremented from 0 to 3 (len is 4 so len-1 is 3), and for each value of k, the element with the index k will be printed. That way, we can print all elements of an array.

Set an element in an array

You can also set an element to a new value with its index using an arrow:

let array1 = [|1; 2; 3; 4|] in
let len = Array.length array1 in
for k = 0 to len-1 do
array1.(k) <- 2 * array1.(k)
done;;
(* array1 = [|2; 4; 6; 8|] *)

In this example, each value of the array is replaced by 2 times the original value.