help with a simple simple probram (i'm new)

[seandugan890]

Hi I am very very new to C, and am working on an assignment for a C programming intro class and I am having a little trouble on my program. The program is supposed to get the users change needed from the input of purchase price and cash tendered, and then print the amount of each coin needed to be given back in change. The problem is that when the program is executed, it gets only to the point of printing the change needed to be given, and then stops. please help me to find my stupid error.
My code is as follows:

int main(int argc, char **argv)		/* Main declaration with arguments           */
{
char x;
int pennies = 0, nickels = 0, dimes = 0, quarters = 0 , halfDollars = 0, dollars =0 , fiveDollars = 0 , tenDollars = 0;
float purchasePrice , cashTendered , cashChange;

//collects imput from user and finds the change needed from those two imputs.
printf("Enter the purchase price including cents ($ddd.cc): $");  
scanf("%f" , &purchasePrice);
printf("Enter amount of cash tendered including cents ($ddd.cc): $");
scanf("%f" , &cashTendered);
                 cashChange = cashTendered - purchasePrice;
printf("Total Change: $%.2f\n" , cashChange); 

//Finds each coin value for the change

while (cashChange >= 00.00){
      while (cashChange >= 10.00){
            cashChange  = cashChange - 10.00 ;
            tenDollars = tenDollars + 1;
      }
      while (cashChange >= 5.00){
            cashChange  = cashChange - 5.00 ;
            fiveDollars = fiveDollars + 1;
      }
      while (cashChange >= 1.00){
            cashChange  = cashChange - 1.00 ;
            dollars = dollars + 1;
      }
      while (cashChange >= 0.50){
            cashChange  = cashChange - 0.50 ;
            halfDollars = halfDollars + 1;
      } 
      while (cashChange >= 0.25){
            cashChange  = cashChange - 0.25 ;
            quarters = quarters + 1;
      }    
      while (cashChange >= 0.10){
            cashChange = cashChange - 0.10 ;
            dimes = dimes + 1;
      } 
      while (cashChange >= 0.05){
            cashChange = cashChange - 0.05 ;
            nickels = nickels + 1;
      }   
      while (cashChange >= 0.01){
            cashChange = cashChange - 0.01 ;
            pennies =pennies + 1;
      }   
}


//prints the value of each coin
printf("Ten Dollar Coins: %d\n" , tenDollars); 
printf("Five Dollar Coins: %d\n" , fiveDollars);
printf("One Dollar Coins: %d\n" , dollars);   
printf("Half Dollar Coins: %d\n" , halfDollars); 
printf("Quarter Coins: %d\n" , quarters);                 
printf("Dime Coins: %d\n" , dimes);    
printf("Nickel Coins: %d\n" , nickels);  
printf("Penny Coins: %d\n" , pennies);  
printf("[Done]\n");  

//exits program
printf(" \n");
    scanf("%c",&x);
    printf(" \n");
    
    printf("Press any key to continue . . . ");
    scanf("%c",&x);  
    exit(0);
}

[kermit]

Do you have access to a debugger? This would demonstrate to you what is happening. Basically, the problem occurs as you break down the change - after a while, you have some change left, but it is less than one hundredth of a cent. So it is 'greater than 0.00', yet does not fit any of the categories which follow it. This is a difficulty of trying to compare floating point numbers.

You ought to have a look at the following for some ideas about what is going on, and what you can do about it.

comp.lang.c FAQ: What's a good way to check for ``close enough'' floating-point equality?

What Every Computer Scientist Should Know About Floating-Point Arithmetic

This next one might be a little helpful too:

IEEE Standard 754 Floating Point Numbers

[seandugan890]

i'm sorry i still don't understand after reading those items, how would I then alter my program so that it rounds them down to the nearest hundredth?

[kermit]

Someone else might offer a better solution, but how about skipping the floating point comparisons, and doing something like have two variables to store your money in - one for the dollars, and one for the cents. You can then use an int type for both, and your comparisons will work as you want them to.

[Elysia]

A good idea to to avoid floating point numbers if possible. An alternate solution could be to simply multiply your money by 100. Floating point numbers are inexact due to the way they work, and that causes problems, especially in comparisons.

[RockyMarrone]

#include <stdio.h>
#include <math.h>

void change(const float cash) {
  int ten_dollars  = 0;
  int five_dollars = 0;
  int one_dollar   = 0;
  int half_dollar  = 0;
  int quarters     = 0;
  int dimes        = 0;
  int nickels      = 0;
  int pennies       = 0;

  float small_denominations = cash - floor(cash);
  int __cash                = floor(cash);

  if (__cash > 0) {
    ten_dollars   = __cash / 10;
    __cash        = __cash % 10;
  }

  if (__cash > 0) {
    five_dollars  = __cash / 5;
    __cash        = __cash % 5;
  }

  one_dollar           = __cash;

  half_dollar          = small_denominations / 0.50f;
  small_denominations  = small_denominations - (half_dollar * 0.5f);

  quarters             = small_denominations / 0.25f;
  small_denominations  = small_denominations - (quarters * 0.25f);

  dimes                = small_denominations / 0.10f;
  small_denominations  = small_denominations - (dimes * 0.10f);

  nickels              = small_denominations / 0.05f;
  small_denominations  = small_denominations - (nickels * 0.05f);

  pennies              = small_denominations / 0.01f;
  small_denominations  = small_denominations - (pennies * 0.1f);

  printf("ten_dollars  == %d\n", ten_dollars);
  printf("five_dollars == %d\n", five_dollars);
  printf("one_dollar   == %d\n", one_dollar);
  printf("half_dollar  == %d\n", half_dollar);
  printf("quarters     == %d\n", quarters);
  printf("dimes        == %d\n", dimes);
  printf("nickels      == %d\n", nickels);
  printf("pennies      == %d\n", pennies);
}

int main() {
  float cash = 0;
  printf("Please enter the cash amount\n");
  scanf("%f", &cash);

  change(cash);

  return 0;
}

Look at the code above may be u can get some help from this

As Elysia said avoid float that is correct because u can see i have to wrote something different from integer calculation but if it is needed than may be the above code can help u in that

and as like every code can be optimized so may be this can be also