My solution to CS50x Problem Set 1 - Cash. Feel free to critique or ask questions.

cash.c

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

float get_positive_float(void);

int main(void)
{
//creates variable "change" (amount of cents due) and varable "coins" (the amount of coins to be given out)
    float change = round(get_positive_float() * 100);
    int coins = 0;

//main code starts to see how many quarters it can take out of the change due, then it moves on to dimes,
//then nickels, and finally pennies
    for (coins = 0; change - 25 >= 0; change = change - 25)
    {
        coins++;
    }
    for (true; change - 10 >= 0; change = change - 10)
    {
        coins++;
    }
    for (true; change - 5 >= 0; change = change - 5)
    {
        coins++;
    }
    for (true; change - 1 >= 0; change = change - 1)
    {
        coins++;
    }

//prints the least amount of coins with which you can give out change
    printf("%i\n", coins);
}

//creates function "get_positive_float" that only accepts postive float values as input
float get_positive_float(void)
{
    float n;
    do
    {
        n = get_float("Change owed: ");
    }
    while (n < 0);
    return n;
}