C :: How To Subtract Evenly

how do I subtract this so that I use the smallest number of $20, $10, $5, and $1 to pay $93? The book tells me to "Divide the amount by 20 to determine the number of $20 bills needed, and then reduce the amount by the total value of the $20 bills. Repeat this for the other bill sizes."I think the part in bold throws me off. What IS the total value of the $20 bills if I use $93 as the example? Is it $80, the highest we can go with $20 bills? Is it 4, the number I got from 93/20 after cutting off the decimal places, also the total number of $20 bills I can use?

I know how to do it and can do it in real life. It's like, "Oh, I need to pay $93. So I use four $20 bills, which brings me to $80. Using one more would bring it to $100, which is too much. So now, I need to use a $10 bill, which brings it to $90. Oh, so now, I need to use three $1 bills, which brings me to $93."But how do I tell that to a computer? It seems like I would have to put some kind of limits on it, or string code lines together,Here is the code so far:

Code:

#include <stdio.h>int main(void)
{
int amount, twenty, ten, five, one;
printf ("Enter a dollar amount:
");
scanf ("%d", &amount);
}

[code]....