Thread: Dispense Change program

Hi,
I need to write a dispense change program.I completed the code,but it has some problem.Please help me to debug the code.

Code:

#include <stdio.h>
#include <math.h>
void change(double coin_change, int *quarters, int *dimes, int *nickels, int *pennies);
int main(void)
{
	int c_dollars, c_quarters = 0, c_dimes = 0, c_nickels = 0, c_pennies = 0;
	double a_paid, a_due, m_change, coin_change;
	printf("Enter the amount paid> ");
	scanf("%lf", &a_paid);
	printf("Enter the amount due> ");
	scanf("%lf", &a_due);
	m_change = a_paid - a_due;
	c_dollars = floor(m_change);
	coin_change = m_change - floor(m_change);
	// shows coin change
	printf("\n%f\n", coin_change);
	change(coin_change, &c_quarters, &c_dimes, &c_nickels, &c_pennies);
	printf("Change is dollars: %d$, quarters: %d, dimes: %d, nickels: %d,\
pennies: %d", c_dollars, c_quarters, c_dimes, c_nickels, c_pennies);
	return(0);
}
void change(double coin_change, int *quarters, int *dimes, int *nickels, int *pennies)
{
	int q = 0, d = 0, n = 0, p = 0;
	 do{
		if(coin_change >= 0.25){
			q++;
			*quarters = *quarters + q;
			coin_change = coin_change - q*0.25;
		}
		else if( coin_change >= 0.10){
			d++;
			*dimes = *dimes + d;
			coin_change = coin_change - 0.1;
		}
		else if( coin_change  >=  0.05){
			n++;
			*nickels = *nickels + n;	
			coin_change = coin_change - (n*0.05);
		}
		else if(coin_change >= 0.01){
			p++;
			*pennies = *pennies + p;
			coin_change = coin_change - (p*0.01);
		}
	}while(coin_change>0);
}

1) If you do some searching on the forum you will find this problem has been here several times before.
2) Exactly what problems are you experiencing, in which parts of your code?

The loop can not be terminated.( do-while loop )

To avoid possible rounding errors, I would multiply by 100 to get a value of 0 to 99 as input into the function.

Tim S.

Originally Posted by paranoidgnu

The loop can not be terminated.( do-while loop )

Code:

do 
  {

} while (coin_change > .01)

There's nothing to do with less than a penny.

Originally Posted by nonoob

coin_change = coin_change - 0.1 is different than the other sections.
Also, the calculation for number of coins is flawed. For example, if you expect 3 quarters...
q = 1
*quarters = *quarters + q; - will add 1
q = 2
*quarters = *quarters + q; - will add 2, total 3
q = 3
*quarters = *quarters + q; - will add 3, total 6

Also, you should work with integer pennies to avoid floating-point roundoff issues.
Change the coin_change to be int, then coin_change = (int)((m_change - floor(m_change)) * 100 + 0.5)
In the function work with 25, 10, 5, 1 (whole numbers).

Thanks nonoob,
The problem has just solved.The right code is here;

Code:

#include <stdio.h>
#include <math.h>
void change(double coin_change, int *quarters, int *dimes, int *nickels, int *pennies);
int main(void)
{
	int c_dollars, c_quarters = 0, c_dimes = 0, c_nickels = 0, c_pennies = 0;
	double a_paid, a_due, m_change, coin_change;
	printf("Enter the amount paid> ");
	scanf("%lf", &a_paid);
	printf("Enter the amount due> ");
	scanf("%lf", &a_due);
	m_change = a_paid - a_due;
	c_dollars = floor(m_change);
	coin_change = (int)((m_change - floor(m_change)) * 100 + 0.5);
	// shows coin change (int)((m_change - floor(m_change)) * 100 + 0.5)
	//coin_change = coin_change * 100;
	printf("\n%f\n", coin_change);
	
	change(coin_change, &c_quarters, &c_dimes, &c_nickels, &c_pennies);
	printf("Change is dollars: %d$, quarters: %d, dimes: %d, nickels: %d,\
pennies: %d", c_dollars, c_quarters, c_dimes, c_nickels, c_pennies);
	return(0);
}
void change(double coin_change, int *quarters, int *dimes, int *nickels, int *pennies)
{
	int q = 1, d = 1, n = 1, p = 1;
	 do{
		if(coin_change >= 25){
			*quarters = *quarters + q;
			coin_change = coin_change - 25;
		}
		else if( coin_change >= 10){
			*dimes = *dimes + d;
			coin_change = coin_change - 10;
		}
		else if( coin_change  >=  5){
			*nickels = *nickels + n;	
			coin_change = coin_change - 5;
		}
		else if(coin_change >= 1){
			*pennies = *pennies + p;
			coin_change = coin_change - 1;
		}
	}while (coin_change >= 1);
}

You can define coin_change to be int, and same with the first parameter of change() to clean things up.
I hope you understand and can explain how the fractional dollars are converted to integer.

Originally Posted by nonoob

You can define coin_change to be int, and same with the first parameter of change() to clean things up.
I hope you understand and can explain how the fractional dollars are converted to integer.

Thanks for your help.
why we added 0.5 to our fractional dollars

Yes I figured you should know that. We multiply the fractional dollars part to make it integer cents. Then add 0.5 (1/2 cent) to round it to the nearest penny.
In case the input is .587 dollars = 59 cents to the nearest cent. Adding 0.5 means the number is rounded up if it exceeds 1/2 cent. Below 1/2 cent it will be chopped.