c , Money Withdrawing Calculator is always off in amount of one dollar bills given

## Question:

Tag: c

I made a program in C that calculates the money to be withdrawn in the least amount of bills possible. Everything works as it should but for some reason, the amount of dollar bills given back is almost always off by one. For example, if I typed in that I wanted to withdraw 549, it would give 5 hundred dollar bills, two twenties, one five, but three dollars instead of four for a grand total of 548. If I wanted 320, it would give -1 dollars back. I'm not sure what's wrong with the program - I checked the math and everything and tried it on different compilers. Any help would be appreciated.

``````#include <stdio.h>

int main()
{
int amountToWithdraw = 0;
int hundredsWithdrawn = 0;
int fiftysWithdrawn = 0;
int twentysWithdrawn = 0;;
int tensWithdrawn= 0;
int fivesWithdrawn= 0;
int onesWithdrawn= 0;

printf ("Please enter the amount of money you wish to withdraw:");
scanf ("%d", &amountToWithdraw);

hundredsWithdrawn = amountToWithdraw / 100;
amountToWithdraw = amountToWithdraw % 100;
fiftysWithdrawn = (amountToWithdraw - hundredsWithdrawn) / 50;
amountToWithdraw = amountToWithdraw % 50;
twentysWithdrawn = (amountToWithdraw - fiftysWithdrawn) / 20;
amountToWithdraw = amountToWithdraw % 20;
tensWithdrawn = (amountToWithdraw - twentysWithdrawn) / 10;
amountToWithdraw = amountToWithdraw % 10;
fivesWithdrawn = (amountToWithdraw - tensWithdrawn) / 5;
amountToWithdraw = amountToWithdraw % 5;
onesWithdrawn = (amountToWithdraw - fivesWithdrawn) / 1;

printf ("You received %d hundred(s)", hundredsWithdrawn);
printf ("You received %d fifty(s)", fiftysWithdrawn);
printf ("You received %d ten(s)", tensWithdrawn);
printf ("You received %d five(s)", fivesWithdrawn);
printf ("You received %d one(s)", onesWithdrawn);

return 0;
}
``````

``````fiftysWithdrawn = (amountToWithdraw - hundredsWithdrawn) / 50;
``````

it should be:

``````fiftysWithdrawn = amountToWithdraw / 50;
``````

and similarly for all the other such lines.

You've already discarded the hundreds (by doing the `amountToWithdraw = amountToWithdraw % 100;`) so you do not need to factor them into the rest of your calculation.

The "off by one" error for `549` comes because on the final step you do `onesWithdrawn = (4 - 1) / 1;` giving `3` when in fact it should be `4`. The `1` was from the bogus use of `fivesWithdrawn`. So I'd expect that you found the off-by-one error for any amounts ending in `5,6,7,8,9` and not for other amounts.

The error doesn't show up for the other notes because the amount of error is smaller than what you're dividing by, e.g. with `549` again, you do `(49 - 5) / 20` to get the number of twenties, but that gives the same answer as the correct version `49 / 20` .

BTW you might want to use the `%=` operator to make your code readable; the way it works is that `A %= B` means `A = A % B`. And use `\n` on the end of your printf.

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