Checking for divisibility?

I'm trying to check the validity of an input to make sure it is a positive multiple of 5. The input will most likely be in the format 0.00, representing a cash amount, to be outputted eventually as coins, excluding pennies. I've got the coin output down, but I can't figure out why the while validation is not working.

The code works for an input of 3.5, the first time I enter it, then I try 3.45 and get the 'invalid' response, then I try 3.5 again and get the 'invalid' response. Is this a result of rounding error?

cashChq = input('Enter the value of the cheque to be cashed: ');
nDollar = floor(cashChq);
centVal = cashChq - nDollar;
vC = centVal*100;

while (cashChq < 0) | (rem(vC,5) ~= 0)
   cashChq = input('Invalid entry; pennies no longer exist! Please enter the value of the cheque to be cashed, \na non-negative dollar amount with cents in multiples of five: ');    
end

nToon = floor(cashChq/2);
toonVal = nToon*2;
amtRem = (cashChq-toonVal);
nLoon = floor(amtRem);
nQrtrs = floor(vC/25);
nDms = floor((vC - nQrtrs*25)/10);
centRem = (vC - nQrtrs*25 - nDms*10);
nNckls = (centRem/5);

fprintf('There are %i toonies, %i loonies, %i quarters, %i dimes, and %i nickels.',nToon,nLoon,nQrtrs,nDms,nNckls);
end

Answer 1

[Christoph F.]

> Is this a result of rounding error?

No, it is the result of a bug. In your while loop, the code inputs a new value for cashChq, but it does not update vC, so the first value of vC is used over and over in the while conditional.