Thread: Trying to convert a total amount into change

I'm trying to convert the total amount left over after a purchase into the correct amount of change. I have written a program but for some reason the dimes go insane and it randomly generates nickels. Can someone tell me why this isn't working?

Code:

#include <stdio.h>
#include <stdlib.h>
#include <math.h>
 
int main()
{
    
       float amountdue;
         
       printf( "Please enter your amount due(in dollars): " );
       scanf( "&#37;f", &amountdue );
       printf( "You have entered %.2f dollars.\n", amountdue );
 
       float amountgiven;
 
       printf( "Please enter the amount given(in dollars): " );
       scanf( "%f", &amountgiven );
       printf( "You have entered %.2f dollars.\n", amountgiven );
       
       float remaining;
       
       remaining = amountgiven-amountdue;
       
       if ( remaining < 0 ) 
       {
            printf( "You do not have enough money!\n" );
       }
       float dollars;
       float quarters;
       float dimes;
       float nickels;
       float pennies;
       
       dollars = 0;
       quarters = 0;
       dimes = 0;
       nickels = 0;
       pennies = 0;
       
       printf ( "You will recieve %.2f back.", remaining );
       
       while ( remaining >= 1 ) {
             remaining = ( remaining - 1 );
             dollars = ( dollars + 1 );        
       }
       printf ( "Amounting to: %.0f dollars,", dollars );
       
       while ( remaining >= .25 ) {
             remaining = ( remaining - .25 );
             quarters = ( quarters + 1 );
       }
       
       printf ( " %.0f quarters,", quarters );
       
       while ( remaining >= .1 ) {
             remaining = ( remaining - 0.1 );
             dimes = ( dimes + 1 );
       }
       
       printf ( " %.0f dimes,", dimes  );
       
       while ( remaining >= .05 ) {
             remaining = ( remaining - 0.05 );
             nickels = ( nickels + 1 );
       }
       
       printf ( " %.0f nickels,", nickels );
       
       while ( remaining >= .01 ) {
             remaining = ( remaining - 0.01 );
             pennies = ( pennies + 1 );
       }
       
       printf ( " and %.0f pennies." , pennies );
            
       
       
      
        system("pause");
       
       exit (0);
 
}

I corrected the problems, but it is off by 1 penny!

Originally Posted by tabstop

For example, $1.68 is actually stored (assuming IEEE floats, but that's what everyone uses these days) as 1.10101110000101000111101 in binary, which is a little under 1.68, which means that when you get down to the last penny, remaining is actually <0.01 by a little bit, hence the last penny doesn't get added in.

Isn't that crazy!!

Money is really about integers anyway. But, NB. That division in C is always rounded down (eg, 11/4 = 2) which might not be fiscally responsible.

edit: this means use modulus (&#37 for the pennies

Code:

int total=11, nickels=total/5, pennies=11%5;

Nickels will be 2 and pennies will be 1.
edit2: looking more closely, modulus is pretty much the key to change making:

Code:

int total=168, quarters=total/25, dimes=(total%25)/10, nickels=((total%25)%10)/5, pennies=((total%25)%10)%5;

...i think

Here's what I meant:

Code:

#include <stdio.h>

int main () {
	int total=168, quarters=total/25, dimes=(total&#37;25)/10, 
                       nickels=((total%25)%10)/5, pennies=((total%25)%10)%5;
	printf("%d %d %d %d\n",quarters,dimes,nickels,pennies);
}

Output:
6 1 1 3
That's $1.68