How would I use recursion to create an array of extra change($100, 50, 20, 10, 5, 1) MATLAB - matlab

Question

How would I correctly make a recursive call within every if-statement to get the change of money? Im specifically focusing on the "change" variable.Thanks
TEST CASE 1-------------------------------------------------------------------------------
<>> [change,flag] = makeChangeRecursive(2,100)
change =
50
20
20
5
2
1
flag =
1
My code is the following
function [change,flag] = makeChangeRecursive(cost,paid)
if extra > 0
flag = true;
elseif extra == 0
change = 0;
flag = true;
return
elseif cost > paid;
flag = false;
change = [];
warning('That''s not enough to buy that item.');
return
end
if extra >= 100
change = [change; makeChangeRecursive(cost,paid - change )];
paid =paid-100;
elseif extra >= 50
change = [change; 50];
paid =paid-50;
elseif
This continues for all dollar values.

Answer 1

Let's take a look at your first case:
if extra >= 100
change = [change; makeChangeRecursive(cost,paid - change )];
paid =paid-100;
elseif ...
The first time we call your function, the variable change doesn't have anything in it. In fact, it will never have anything in it at the beginning of the function call because you don't pass it in as a parameter or give it a value prior to this line. So putting change on the right-hand side of the assignment will give you an error.
But that's okay, because that's not what you want to do anyway. You want to build change up from the beginning.
In addition, change is a list of values. We want to pass the recursive calls a single value, paid after updating its value.
Let's build this up step by step:
if extra >= 100
If this is true, we want subtract 100 from the amount paid (what we pass in to the recursive call) and add 100 to our list of change. Let's do the first part:
paid = paid - 100;
As I said, we want to update paid first because we're going to use this value in the recursive call, which happens next, along with adding our new change value to the list:
change = [100; makeChangeRecursive(cost, paid)];
elseif ...
And so on for the remainder of the change values. I'm sure you can take care of the rest of them now by yourself.
I also noticed that you didn't assign a value to extra. This might have been just a cut-and-paste error, but you need to make sure that you have that at the beginning of your function.