Arrays

Arrays are collections of items. Each item in an array must be of the same data type.

Arrays are also a set size: we can’t change our mind and adjust the size later.

Creating an array

Default values

One way to create an array is to simply identify the data type, and set the size:

const int ARRAY_SIZE = 5;
int[] myInts = new int[ARRAY_SIZE];

This means all elements in this array will be of type int, and there are 5 elements. Unless I initialize the value, they will all hold the default value for that data type.

ints have a default value of 0, so right now, that array looks like:

index:	0	1	2	3	4
value:	0	0	0	0	0

💡 Remember: indexes start at 0, not 1.

---

Loading data

Alternatively, we can load data into the array at the same time as we create it:

string[] dayOfWeek = new string[7] {
        "SUN", "MON", "TUE", "WED", "THU", "FRI", "SAT" };

Since we’ve provided 7 values, we’ve indirectly already provided the array size, so we can even drop the new string[7] part:

string[] dayOfWeek = { 
    "SUN", "MON", "TUE", "WED", "THU", "FRI", "SAT" }; 

Both will result in an array that can be represented like this:

index:	0	1	2	3	4	5	6
value:	"SUN"	"MON"	"TUE"	"WED"	"THU"	"FRI"	"SAT"

---

Accessing elements in an array

Once an array exists, we can view or modify each element by using square brackets and the index of the element:

const int ARRAY_SIZE = 10;
int[] someNumbers = new int[ARRAY_SIZE];
someNumbers[0] = 5;

I just set the 0th element of the array to the value 5. The contents of my array are now:

index:	0	1	2	3	4	5	6	7	8	9
value:	5	0	0	0	0	0	0	0	0	0

Because we know exactly how many elements are in the array, I could then loop through each element and set each value:

const int ARRAY_SIZE = 10;
int[] someNumbers = new int[ARRAY_SIZE];

for (int index = 0; index < ARRAY_SIZE; index++) {
    someNumbers[index] = 6; // set every element to the value 6
}

We can assign values to the element using literals (as shown in the previous example), using variable names, or expressions. We can also leverage the .Length property, which returns the number of elements in an array.

const int ARRAY_SIZE = 10;
int[] someNumbers = new int[ARRAY_SIZE];
Random numberGenerator = new Random();

for (int index = 0; index < someNumbers.Length; index++) {
    someNumbers[index] = numberGenerator.Next(1,11);
}

Sorting arrays

Array.Sort() will sort the elements in a 1-dimensional array.

int[] myArray = new int[5] { 6, 4, 7, 2, 8 };
Array.Sort(myArray); // now array is: {2, 4, 6, 7, 8}

Multi-dimensional arrays

We are not limited to creating 1-D arrays: here is an example of creating a 3x3 (or 2-Dimensional) array.

int [,] board = new int [3,3]; // first digit is the row, 2nd digit is the column
board [1,1] = 1;

We’ve created a 3x3 array, and then set the element in the 1st row and 1st column to the value 1:

indices	0	1	2
0	0	0	0
1	0	1	0
2	0	0	0