Greedy numbers between 0 and 1 .... and 4.2

Question

I have good number of coins for number over 1 with decimal (ex: 2.7, 5.1). And wrong number of coins only with numbers between 0 to 1 (0.99 or 0.41): always 0. plus the check50 says that it doesn't work with 4.2! Please could you hint me what could be my error because I have the integer already so I have no ideas. here is my code :

#include <cs50.h>
#include <stdio.h>

int main (void)

{
    int conversion;
    float change;
    int amount = 0;

    do 
    {
        printf("O hai! How much change is owed ?");
        change = get_float(); 

    }
    while (change < 0);

    conversion = (int) change * 100;


    while (conversion >= 25)
    {
        amount ++;
        conversion = conversion - 25;
    }

    while (conversion >= 10)
    {
        amount ++;
        conversion = conversion - 10;
    }

    while (conversion >= 5)
    {
        amount ++;
        conversion = conversion - 5;
    }

    while (conversion >= 1)
    {
        amount ++;
        conversion = conversion - 1;
    }

    printf("%d\n", amount);

 } 

thanks a lot.

Answer 1

A quick peak at the Hints section in the spec might help you identify the problem.

Do beware the inherent imprecision of floating-point values. [...] And take care to round your cents (to the nearest penny); don’t "truncate" (i.e., floor) your cents!

In your program, you don't round your cents - you instead just multiply the float (change) by 100, and then convert that to an int. But what about the small imprecision of floating-point values, like the spec said? Try printing a float's value to 55 decimal places. You can use the spec's example:

float f = 0.1;
printf("%.55f\n", f);

What does this print? 0.1000000014901161193847656250000000000000000000000000000! We expect it to print 0.1 then a whole bunch of zeros, right? Clearly, there is an imprecision! That's why it is so important that you use a function like roundf (in the math.h library), which rounds to the nearest integer.

If this answers your question, please hit the green checkmark. If you still have issues, comment below.