Arrays

An array holds multiple values of the same type in a sequence. Each value is accessed by its index (position).

Declaring an Array

Use Type[] syntax:

int[] numbers;
numbers = [10, 20, 30, 40];

string[] names = ["John", "Alice", "Bob"];

Default Value

An uninitialized array variable starts at null. You must assign it before use:

int[] items;
// print(items[0]);       ERROR, array is null

items = [1, 2, 3];        // now it's ready

Accessing Elements

Use square brackets with the index. Indices start at 0:

int[] arr = [10, 20, 30];

print(arr[0]);            // 10
print(arr[1]);            // 20
print(arr[2]);            // 30

arr[1] = 99;              // change value at index 1
print(arr[1]);            // 99

Out of Bounds

Accessing an index that doesn’t exist causes a runtime error that can be caught with try/catch:

int[] arr = [1, 2, 3];

try {
    print(arr[99]);       // index out of bounds
} catch (Error e) {
    print(e.code);
}

Reference Semantics

Arrays are reference types: assigning one array to another shares the same data:

int[] a = [1, 2, 3];
int[] b = a;              // b refers to the same array

b[0] = 99;
print(a[0]);              // 99, a changed too!

Built-in Array Methods

Arrays come with several built-in methods. Use dot syntax to call them:

int[] arr = [10, 20, 30];

int len = arr.length();     // 3, number of elements
arr.push(40);               // add to end  → [10, 20, 30, 40]
int last = arr.pop();       // remove end  → 40, arr is [10, 20, 30]
arr.reverse();              // reverse in-place → [30, 20, 10]

Full list:

Method	Returns	Description
arr.length()	int	Number of elements
arr.push(val)	int	Add to end (returns new index)
arr.pop()	E	Remove and return last element
arr.insert(index, val)	int	Insert at position (returns index)
arr.remove(index)	E	Remove and return element at index
arr.slice(start, end)	E[]	New array from range [start, end)
arr.reverse()	E[]	Reverse in-place (same reference returned)
arr.concat(other)	E[]	New array combining both
arr.contains(val)	bool	Check if value exists
arr.indexOf(val)	int?	Find index (returns null if not found)
arr.clear()	void	Remove all elements

Some of these methods (push, pop, insert, remove, reverse, clear) change the array in place, and because arrays are shared references, that change is visible through every variable pointing at the same array. See the Built-in Functions page for a from-scratch walkthrough of each method, including which ones mutate.

Looping Through Arrays

string[] names = ["John", "Alice", "Bob"];

for (int i = 0; i < 3; i = i + 1) {
    print(names[i]);
}
// Output: John Alice Bob

Arrays with Structs

You can store structs in arrays:

struct Person {
    string name;
    int age;
}

int main() {
    Person p1;
    p1.name = "John"; p1.age = 30;

    Person p2;
    p2.name = "Alice"; p2.age = 25;

    Person[] people = [p1, p2];

    print(people[0].name);    // "John"
    print(people[1].age);     // 25

    people[0].age = 31;       // modify through array
    return 0;
}

Arrays of Nullable Types

int?[] values = [10, null, 30, null, 50];

for (int i = 0; i < 5; i = i + 1) {
    if (values[i] != null) {
        print(values[i]);
    }
}
// Output: 10 30 50

Common Patterns

Sum all elements

int sum(int[] arr) {
    int total = 0;
    for (int i = 0; i < arr.length(); i = i + 1) {
        total = total + arr[i];
    }
    return total;
}

Find max

int findMax(int[] arr) {
    int result = arr[0];
    for (int i = 1; i < arr.length(); i = i + 1) {
        if (arr[i] > result) {
            result = arr[i];
        }
    }
    return result;
}

What’s Next?

• Work with text using strings
• Handle errors with try/catch/throw