We have two unrelated problems:

1. while the get and set inside subscript work fine they do not work on their own so I guess we are not using the correct syntax
2. For the custom convertible description we want it to be the 2D array however, when we try to set it up we run into a problem that we need to use the variable matrix (where the array data is stored) but it is not initialized until runtime so we get an error. Not sure how to correct it.

import Foundation

import Foundation
import Glibc

struct Array2D: CustomStringConvertible {
var numberRows: Int
var numberCols: Int
var matrix: [Int]
var description: String = ""

init(numberRows: Int, numberCols: Int) {
self.numberRows = numberRows
self.numberCols = numberCols
matrix = Array(repeating: 0, count: numberRows * numberCols)
for d in 1...numberRows {
description += "(matrix[(d - 1) * numberCols...(d * numberCols) - 1]) \n"
}
}

func index(row: Int, col: Int) -> Int {
return (numberCols * (row - 1) + (col - 1))
}

func indexIsValid(row: Int, col: Int) -> Bool {
if col > numberCols || row > numberRows {
return false
} else {
return true
}
}

/* set(row: Int, col: Int, newValue) {
{
if indexIsValid(row: row, col: col) {
matrix[(row * numberCols) + col] = newValue
} else {
print("index is out of bounds")
exit(0)
}
}
}

}
get(row: Int, col: Int) -> Int {
return data[(index(row: row, col: col))]
}
*/

subscript(row: Int, col: Int) -> Int {
get {
if indexIsValid(row: row, col: col) {
return matrix[index(row: row, col:col)]
} else {
print("inxex is out of bounds")
exit(0)
}
}
set(newValue) {
if indexIsValid(row: row, col: col) {
matrix[index(row: row, col: col)] = newValue
description = ""
for d in 1...numberRows {
description += "(matrix[(d - 1) * numberCols...(d * numberCols) - 1]) \n"
}

} else {
print("index is out of bounds")
exit(0)
}
}
}

}

Managed to solve the problem of the custom string convertible (in a very non efficient way I am sure).
So now the code is working and doing what it should. Still not sure how to implement the get and set not inside subscript.