Thread: Brand New to C; First Program and a Couple of Questions

Hey guys! I'm brand new to C and I'm having a hell of a hard time so far. I'm currently writing one of my first programs for my class and I'm completely suck. We're supposed to write a cash back program where a user enters a dollar amount up to $100 and they get their change back in twenties, tens, fives, ones, quarters, dimes, nickels, and pennies.

The amount entered has to be a double and I don't understand how I can divide a double by another double, and then take the remainder and use it for another dollar value.

Any help is MUCH appreciated! My current code is below. Thanks!

Code:

#include <stdio.h>#include <stdlib.h>




int main()
{
    float twenties;
    float twentiesRemainder;
    float tens;
    float fives = 5;
    float ones = 1;
    float quarter = .25;
    float dime = .10;
    float nickel = .05;
    float penny = .01;
    double dollarEnt;


    /*Get the total input amount*/
    printf("Please enter a dollar amount up to 100:  ");
    scanf("%lf", &dollarEnt);


    twenties = (dollarEnt/(20));
    if (twenties>=1)
        printf("%.0lf twenties", twenties);


    tens = (twenties/(10));
    if (tens>=1)
        printf("%.2lf tens", tens);
    if (fives>=1)
        printf("%.2lf", fives);
    if (ones>=1)
        printf("%.2lf", ones);
    if (quarter>=1)
        printf("%.2lf", quarter);
    if (dime>=1)
        printf("%.2lf", dime);
    if (nickel>=1)
        printf("%.2lf", nickel);
    if (penny>=1)
        printf("%.2lf", penny);








    system("Pause");
    return 0;
}

Thank you for the reply, but I'm not even sure what that means exactly. I looked up fmod() and tried using it but failed.

I don't agree with using new never-before-seen functions from the math.h library will be the best approach that a beginner should be taking.

thepsionicstorm, have you used for or while loops yet? What you could do is

Code:

int i;

for (i=1; i<=5; i++) {
    twenties = dollarEnt/20;
    if (twenties == i) {
        printf("%d twenties", i);
    }
}

Notice the for loop goes up to i == 5 because that's the max amount of 20's you can have (100/20 = 5).

What you could do is

Yes. It wouldn't necessarily work because of the use of floating point values, but it could work.

The question is, why would you do that?

Most of the variables that you've declared as floats should probably be ints.

Yeah.

There is no reason for this to be so complicated as you've made it out to be or involve floating point mathematics in any way.

You have a $100.00 maximum value; that's 10000 pennies.

I myself have been studying C for over half a year now and I have no clue of what to make with what you just said, so I really doubt the OP will either.

*shrug*

It isn't the best suggestion posted, but the posts grumpy made are the only posts that contains an actual answer to the question.

If you need the remainder of a floating point operation you need to use `fmod'.

I suppose you could do the operation "long hand", but that would be kind of weird.

Soma

lol thank you guys. thank you @grumpy, although i didn't understand what you were saying.

@Mentallic, yes I am just starting to play with loops; I am by no means proficient in them yet though.

@oogabooga, that worked fantastic! I do have 2 questions though:
1. How did you know that would work? What was your process for figuring that out, so that I might be able to follow your logic the next time I encounter this problem or am able to help someone myself.
2. The code you gave me works for 20's, 10's, 5's, and 1's as Ints, but how would I apply this code to work with quarters (.25c), dimes (.10c), nickels (.05c), and pennies (.01c)?

Thank you all so incredibly much!

although i didn't understand what you were saying.

Really?

The `fmod' thing is a function just like `printf' is a function.

To use `fmod' correctly in your code you need the prototype just like you need the prototype for `printf' in order to use it; the prototype for `fmod' can be found in the "math.h" header.

The environment, IDE or whatever, may be setup by default in such a way that it will not work without changing something. (This has nothing to do with programming. It is like configuring a game to use "2x" or "4x" anti-aliasing. It is just a part of using, and knowing how to use, the tools you have installed to support your programming work.)

How did you know that would work?

He has experience with programming and mathematics.

What was your process for figuring that out, so that I might be able to follow your logic the next time I encounter this problem or am able to help someone myself.

Continue to do your practice work over a long enough period of time and it will soon come naturally... whether or not you want it to come.

Soma

@phantom, really.
1. I've been exposed to see an entire 3 weeks or so along with 15 other units at school and a job, trying to learn as much of this as I can when I actually have the time to.
2. I was not asking for why he knew it would work because of his overall experience in a certain field, but rather for his reasoning regarding the particular piece of code.
3. Thank you; I will continue to practice and would obviously not be putting in the time I currently am and taking the step of asking other generous people for help if I didn't desire to learn this material.

rather for his reasoning regarding the particular piece of code

O_o

If you have a bunch of things and sort them into as many groups of `count' as possible, with a remainder group of an unknown quantity strictly less than `count', you have `group_count' groups.

If you take all the complete groups, the ones with `count', and add them back into one big group you are left with only the remainder group.

This is remarkably simple mathematics.

You are clearly too close to the problem to see a solution.

No, really, there is no intent to offend here; you need to back away from the problem and programming in general and just work the solution out on paper.

Soma

@WaltP, thank you for your reply. I sort of get what you mean by making dollars into cents, but I'm not sure how I would do that with my current code. I will include the code below; I am able to input a whole number and get the correct results ($44 = 2 twenties, 4 ones), but also what shows up is '0 tens, 0 fives'.

1. How could I make it so that the values that would be 0 do not show up.
2. How can I alter my current code to integrate cents from .25, .10, .05, and .01? I added the .25 cents code (quarter) below the ones (ones), but when I put in an input value such as $44.50, the number of quarters never show up.

Thank you all again!