Need help understanding this c++ question

If I was approaching this homework problem this is what I would do ...

Q1. CanDispense(amt)
- Can I divide amt by 50 and if so is there anything left?
- Can I divide the remainder by 20 and if so is there anything left?
- If I take the number of 50's plus the number of 20's does it equal amt?

So I'm going to need Integer Division (/) and possibly the remainder (modulus[^])

Q2. Dispense50s(amt)
- Can I divide amt by 50 and what is the result?

So I'm going to need Integer Division (/). And nothing else really - I'll either get 0 (zero) or the number of 50-bills I need.

Hang on a minute, that Dispense50s function could be called from the CanDispense function. Hm ... I could do a Dispense20s function as well and use that in the CanDispense function too.

So now my CanDispense function is going to look like
1. How many 50's do I need
2. How Many 20's do I need
3. If I add up all the bills I have does it equal the original amount?

Member 12343138102 said:

So assuming in Q1, if I got 5 bills of 50 and 2 bills of 20, then in Q2, it will means that the answer is 5?

No. See the quote from Kornfield Eliyahu Peter. Your homework as it stands does not ask you to get the number of 50-bills in Q1. However if you look at my train-of-thought you can use that information the other way around ... so you were actually on the right track.

Member 12343138102 said:

Also was wondering in cases like this, is it alright to print out any output message that state how many bills of 20s and 50s you will be getting based on the above questions?

That is entirely up to you, and possibly your tutor. Certainly it's a good idea when debugging but you might not want it in your final program. It's likely to be the next stage in the assignment anyway :)

Give it a go, and come back if you get stuck on the actual results

Ok, you have changed the original question by adding the piece of code you wrote and you still want extra guidance:

xenas19[^] wrote:

The reason I have asked this (question) is mainly because I am not even sure if I am on the right track. Just want to have some assurance

So...
CanDispense function is wrong. I don't want to explain why, i prefer to explain how to write proper function.

Because you're a beginner...

Imagine, you have got only 2 types of coins/notes: 20 and 50, similar to cash machine. Someone wants to get his money, let's say 170$. Inside CanDispense function you should check all possible combinations of 20's and 50's which will give you a 170$. How to achieve that? In pseudo code:

//all banknotes: 
int[] coins = {20,50};
//amount to exchange/dispense
int amt = 170;
//get the max. count of ... 
//20's in amount - in this case 8 plus some value after decimal separator
int a = (int)(amt / coins[0])+1;
//50's in amount - in this case 3 plus some value after decimal separator
int b = (int)(amt / coins[1])+1;
//+1 is extra added - why? you'll see in next step
//now you have to find all possible combinations of 20's and 50's to dispense requested amount of money
//the simplest way to "visualize" that is to create 2-dimensional array which will hold the sum of 20*n + 50*n, where "n" is a multiple of banknote
//you don't need to create it, because your function should return true if it finds the first match (the others are unimportant).
int[,] ways = new int[a,b];

A table should looks like:

iteration	0	1	2	3
0	0	50	100	150
1	20	70	120	170
2	40	90	140	190
3	60	110	160	210
4	80	130	180	230
5	100	150	200	250
6	120	170	220	270
7	140	190	240	290
8	160	210	260	310

As you can see, the requested amount is possible to achive only with 2 combinations, when you get

1x20 + 3x50 = 170<br />
6x20 + 1x50 = 170

How to fill a table and check if a sum of 20's and 50's is equal to requested amount? Using 2 loops:

for (int i = 0; i<a; i++)
{
	for (int j = 0; j<b; j++)
        {
                //k & l are used to show a way how to calculate multiple
                //do not create additional variables if they are unnecessary
		int k = a-(a-i);  //calculate multiple of 20's 
		int l = b-(b-j);  //calculate multiple of 50's
                //as i mentioned, array is used to visualize data only! 
		ways[i,j] = coins[0]*k + coins[1]*l;  //calculate a sum 
		if (ways[i,j]==amt)
			return true;//Console.WriteLine("{0}x{1}+{2}x{3}={4}", i, coins[0], j, coins[1], ways[i,j]);
	}
}
return false;  //a payment is impossible

Got it?