CODEWITHSUNDEEP
ccs50greedy
Reagan Pfifer
Reagan Pfifer

Reputation: 9

Greedy algorithm compiles with no errors but never gets past first action when run

So I am taking cs50 and I am doing the greedy algorithm "cash" problem, and the code I've written compiles fine, but when I run it, it asks for "Change amount in USD:" and then never accepts a valid response and I'm stuck entering inputs forever and nothing happens.

A friend said that I was missing an input and that's why it wasn't working, but I'm trying to use the user's input, so... Your help would be greatly appreciated, because I think I'm really close, I just have not idea how to fix it, and help50 says that technically nothing's wrong, so I'm just at a stand still.

Thank you!

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

int main(void)
{
    // identifying variables
float amount;
int cents;
int count = 0;

// prompting user for input
do
{
    amount = get_float("Change amount in USD: ");
}
// ensuring a positive number
while (amount < 0);

//changing float to an int
    cents = round(amount*100);

// using highest denomination first (quarters)
while (cents % 25 >= 0)
{
    count++;
    cents = cents % 25;
}

// using next highest denomination second (dimes)
while (cents % 10 >= 0)
{
    count++;
    cents = cents % 10;
}

// using next highest denomination third (nickels)
while (cents % 5 >= 0)
{
    count++;
    cents = cents % 5;
}

// using last denomination amount (pennies)
while (cents % 1 >= 0)
{
    count++;
    cents = cents % 1;
}

// displays number of coins used
printf("%i\n", count);

}

Upvotes: 0

Views: 66

Answers (3)

spicy.dll
spicy.dll

Reputation: 957

The problem lies in this bit of code (and those like it)

// using highest denomination first (quarters)
while (cents % 25 >= 0)
{
    count++;
    cents = cents % 25;
}

This will result in an infinite loop based on the principle that any_integer_value % 25 is always >= 0. However, the problem actually doesn't require a mod operation at all. Instead, check if subtracting the coin's value is >= 0 and if it is, do the subtraction.

// using highest denomination first (quarters)
while (cents - 25 >= 0)
{
    count++;
    cents = cents - 25;
}

Upvotes: 0

David Ranieri
David Ranieri

Reputation: 41036

while (cents % 25 >= 0)
{
    count++;
    cents = cents % 25;
}

The division willl always be >= 0, thus you have an infinite loop, switch to 

while (cents % 25 > 0)

Upvotes: 1

Roim
Roim

Reputation: 3066

Your are stuck in infinite loop since your logic is wrong. Take a look in a while loop, for example:

while (cents % 25 >= 0)
{
    count++;
    cents = cents % 25;
}

modules operation will give you a number between 0 and 24. The condition will always be true regardless of what cents original value was.

You want to update your condition to a different one. take notice that inside your while you should update cents differently, since after the first iteration cents values will not change: let's say it is 10. It enters the while loop, and then cents=cents%25 will stay 10. Still infinite loop

Upvotes: 0

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