# Arrays

The arrays in Nim are like classic C arrays, their size is specified at compile-time and cannot be given or changed at runtime.

type
let names: ThreeStringAddress = ["Jasmine", "Ktisztina", "Kristof"]
let addresses: ThreeStringAddress = ["101 Betburweg", "66 Bellion Drive", "194 Laarderweg"]

The size of the array is encoded in its type and cannot be accidentally lost. Therefore, a procedure taking an array of variable length must encode the length in its type parameters.

proc zip[I, T](a, b: array[I, T]):
array[I, tuple[a, b: T]] =
for i in low(a)..high(a):
result[i] = (a[i], b[i])

let nameAndAddresses = names.zip(addresses)

Alternate methods of indexing arrays are also allowed, the first type parameter is actually a range (just a value, as above, is syntactic sugar for 0..N-1). It’s also possible to use ordinal values to index an array, effectively creating a lookup table:

type
PartsOfSpeech {.pure.} = enum
let partOfSpeechExamples: array[PartsOfSpeech, string] = [
"he", "reads", "the", "green", "book", "slowly"
]
type
Matrix[W, H: static[int]] =
array[1..W, array[1..H, int]]

let mat1: Matrix[2, 2] = [[1, 0],
[0, 1]]
let mat2: Matrix[2, 2] = [[0, 1],
[1, 0]]

proc +[W, H](a, b: Matrix[W, H]):
Matrix[W, H] =
for i in 1..high(a):
for j in 1..high(a):
result[i][j] = a[i][j] + b[i][j]

# See $ from the procs section echo mat1 + mat2 $ nim c -r matrix.nim
1, 1,
1, 1,