making greedy algorithm work for every input - c

Question

I wrote a code for greedy algorithm of cs50. It works for inputs between 0 and 1. How can I make it work to inputs like 4.2 , 6.5 , 8 etc?. I have listed my code below. What should I modify in the program?
#include<stdio.h>
#include<cs50.h>
#include<math.h>
int main()
{
int count , change;
float cents;
printf("Enter the change amount : ");
cents = GetFloat();
cents = cents * 100;
change = round(cents);
count = 0;
while(cents < 0 )
{
printf("Enter a positive number : ");
cents = GetFloat();
}
while (change >= 25)
{
change = change - 25;
count++;
}
while (change < 25 & change >= 10)
{
change = change - 10;
count++;
}
while (change < 10 & change >= 5)
{
change = change - 5;
count++;
}
while (change < 5 & change >= 1)
{
change = change - 1;
count++;
}
printf("Total number of coins used : " );
printf (" %d " , count );
printf("\n");
}

Answer 1

I believe that your problem is that you are using bitwise logical operators. You should use && in your comparisons to compare the values of two expressions. There are other little issues: The loop that guarantees positive input should multiply cents by 100 and round(), before assigning this new value to change. But you don't actually need both change and cents. And you don't need as many comparisons as you have written, and without the extra comparisons, you don't need the logical operators that were causing you trouble in the first place!
Edit
I noticed that a number like 4.20 was being rounded first, then multiplied by 100! Of course this is wrong, giving the same results for 4.20, 4.75, and 4. I changed the code below accordingly, but your original code was doing this part correctly (except in the input validation loop, as mentioned earlier). Now the program correctly handle such inputs.
Here is a cleaned-up version (I don't have the cs50.h library, so there are some small differences):
#include <stdio.h>
#include <math.h>
int main(void)
{
int count;
float cents;
printf("Enter the change amount: ");
scanf("%f", &cents);
cents = (float)round(cents * 100);
count = 0;
while (cents < 0) {
printf("Enter a positive number: ");
cents = (float)round(cents * 100);
}
while (cents >= 25) {
cents -= 25;
count++;
}
while (cents >= 10) {
cents -= 10;
count++;
}
while (cents >= 5) {
cents -= 5;
count++;
}
while (cents >= 1) {
cents -= 1;
count++;
}
printf("Total number of coins used: %d\n", count);
return 0;
}