Making change with coins, problem (greedy algorithm)

I'm trying to write (what I imagine is) a simple matlab script. I want to be able to input some amount of cents from 0-99, and get an output of the minimum number of coins it takes to make that amount of change. For example, if I put in 63 cents, it should give

coin = [2 1 0 3]

meaning: 2 quarters, 1 dime, 0 nickles, and 3 pennies

Here's where I am at now:

    function[money] = change(money)
    money = [quarter dime nickle penny];

    %initial amounts of each coin
    quarter = 0;
    dime = 0;
    nickle = 0;
    penny = 0;
    money = true;

    while money>=0
            if money >= 25
                    money = money - 25;
                    quarter = quarter + 1;

            elseif money >= 10
                    money = money - 10;
                    dime = dime + 1;

            elseif money >= 5
                    money = money - 5;
                    nickle = nickle + 1;

            elseif money >= 1
                    money = money - 1;
                    penny = penny +1

            end
    end
    clear;clc;

And then this is the error I get from matlab, "Line: 6 Column: 1 "penny" previously appeared to be used as a function or command, conflicting with its use here as the name of a variable. A possible cause of this error is that you forgot to initialize the variable, or you have initialized it implicitly using load or eval."

What (probably very obvious) thing am I missing?

Answer 1

[Srinivas]

you are writing on to money again and you have an infinite loop

    function[coins] = change12(money)
  %initial amounts of each coin 
  quarter = 0; 
  dime = 0; 
  nickle = 0; 
  penny = 0; 
  % money = [quarter dime nickle penny]; money =[0 0 0 0]
  while money>0 % while money>=0  makes an infinte loop
  if money >= 25 
  money = money - 25; 
  quarter = quarter + 1;
  elseif money >= 10 
  money = money - 10; 
  dime = dime + 1;
  elseif money >= 5 
  money = money - 5; 
  nickle = nickle + 1;
  elseif money >= 1 
  money = money - 1; 
  penny = penny +1;
  end 
  end 
  coins = [quarter dime nickle penny];

Answer 2

[Geoff]

Have already voted on Srinivas' correct answer to your question, but this is for your interest and study:

function [coins] = change( money )
    values = int32([25,10,5,1]);
    remain = int32(money)
    coins = zeros(1,4);
    for v = 1:4
        coins(v) = idivide(remain, values(v));
        remain = mod(remain, values(v));
    end
end

There's far less than can go wrong here, and you can even play with the priority of each denomination by reordering the values array. =)

-g-

Answer 3

[Walter Roberson]

You have the line

      money = [quarter dime nickle penny];

when none of those variables have been initialized. MATLAB is analyzing and saying that the only way that could happen and it be valid is if you happen to have functions with those names.

You cannot use a variable name until after the variable has been initialized.

[Edward]

function[money] = change(money)

%initial amounts of each coin

quarter = 0;

dime = 0;

nickle = 0;

penny = 0;

money = [quarter dime nickle penny];

while money>=0

if money >= 25

money = money - 25;

quarter = quarter + 1;

elseif money >= 10

money = money - 10;

dime = dime + 1;

elseif money >= 5

money = money - 5;

nickle = nickle + 1;

elseif money >= 1

money = money - 1;

penny = penny +1

end

end

clear;clc;

It still does not work. I tried to run it, and matlab couldn't do it. Is there something else I may be missing?

Answer 4

[Image Analyst]

You might try returning the answers instead of money, which will be zero because you decremented it until it was zero:

function [quarter dime nickel penny] = change(money)