Currency Converter with for loop question

I am working on this assignment where the program converts 3 US dollar amts into Danish Krones, Euros & Hong Kong Dollars. I have the program running but i am assuming some coding is wrong in my for loop. the 1st time it runs through the conversions are correct but the 2nd & 3rd time the conversions take the old conversion then multiply the new dollar amt to it creating a huge incorrect number. here is my code and help is appreciated.

Code:

#include <stdio.h>


int main (void)
{
    /*Variable declarations*/
    float usdollar = 0, krones = 0, euros = 0, hkdollars = 0, total = 0;
    int us_conversion = 3, i;
    
        /*Welcome and program description*/
    printf("Welcome to the Bombard Money Exchange\n\n");
    printf("The program will convert three US dollar amounts to\n
Danish Krones, Euros and Hong Kong Dollars.\n\n");
    
    /*User enters exchange rates*/
    printf("First, Please enter the exchange rates:\n");    


    printf("Danish Krones: ");
    scanf("%f", &krones);     
    fflush (stdin);    


    printf("Euros: ");
    scanf("%f", &euros);    
    fflush (stdin);    


    printf("Hong Kong Dollars: ");
    scanf("%f", &hkdollars);     
    fflush (stdin);        
    
    /*loop to convert 3 amounts of US Dollars*/
    
    for (i=1; i <= us_conversion; ++i)
    {
        printf("\n\nEnter US Dollars #%i to be converted: ", i);
        scanf("%f", &usdollar);
        fflush (stdin);
    
        printf("\n%.2f US dollars is equivelent to:\n\n ", usdollar);
        krones = krones * usdollar;
        printf("\t%.2f Danish Krones\n", krones);
        euros = euros * usdollar;
        printf("\t%.2f Euros\n", euros);
        hkdollars = hkdollars * usdollar;
        printf("\t%.2f Hong Kong Dollars\n", hkdollars);
        total = total + usdollar;
    } /*end for loop*/
    
    total = (float) total + usdollar;
    printf("\n\nYou have converted a total of $%.2f\n", total);
}
/*end main*/

The problem is that you are disturbing the user entered conversion rates in your calculations...

Try it like this instead...

Code:

        printf("\n%.2f US dollars is equivelent to:\n\n ", usdollar);
        //krones = krones * usdollar;
        printf("\t%.2f Danish Krones\n", krones * usdollar);

You should get rid of all those fflush(stdin) calls.
SourceForge.net: Fflush - cpwiki

> krones = krones * usdollar;
> printf("\t%.2f Danish Krones\n", krones);
And what will be your exchange rate on the next iteration of the loop?

Perhaps if you had a more meaningful name, say dollarsToKrones, the (il)logic would be more apparent?

Originally Posted by Salem

You should get rid of all those fflush(stdin) calls.

Thanks for the help. My professor wants us to use the fflush(stdin) after each scanf statement in our code...

the sample the exchange rates would be:
5.74087 danish krones
.770602 euros
7.77639 hong kong dollars

with US dollar amts of 12.95, 32.00, 10

Originally Posted by Rebecca Bombard

Thanks for the help. My professor wants us to use the fflush(stdin) after each scanf statement in our code...

Your professor is WRONG. With rare exception flushing an input stream is undefined behaviour. fflush() is designed to ensure that output streams are written to their targets ... for files this means written to disk, for the screen it means shown on the display... stdin is NOT an output stream...

As Quzah would say... you don't flush a faucet... do you?

Post this to your "professor".

Originally Posted by c99

7.19.5.2 The fflush function
Synopsis
1
#include <stdio.h>
int fflush(FILE *stream);
Description
2 If stream points to an output stream or an update stream in which the most recent
operation was not input, the fflush function causes any unwritten data for that stream
to be delivered to the host environment to be written to the file; otherwise, the behavior is
undefined.
3 If stream is a null pointer, the fflush function performs this flushing action on all
streams for which the behavior is defined above.
Returns
4
The fflush function sets the error indicator for the stream and returns EOF if a write
error occurs, otherwise it returns zero.

Do you see "input" mentioned (in the affirmative sense) anywhere?
Index of /jtc1/sc22/wg14/www/docs/n869

Is this same "professor" also rotting your brain by using TurboC as the course compiler by any chance?

Originally Posted by Salem

Is this same "professor" also rotting your brain by using TurboC as the course compiler by any chance?

no, he suggests we use C free but doesn't require a specific complier. i looked at my syllabus and it states -2 points for anytime fflush (stdin) is not used. so i thank you for pointing that out and i will keep it in mind, but for my assignments i'll keep it in for my professor to be happy.

fyi: i figured out my issue by assigning more variables so that the exchange rates have a different variable than the conversion; so my equations would be

krones = us_to_krones * us_dollar

Originally Posted by Rebecca Bombard

no, he suggests we use C free but doesn't require a specific complier. i looked at my syllabus and it states -2 points for anytime fflush (stdin) is not used. so i thank you for pointing that out and i will keep it in mind, but for my assignments i'll keep it in for my professor to be happy.

fyi: i figured out my issue by assigning more variables so that the exchange rates have a different variable than the conversion; so my equations would be

krones = us_to_krones * us_dollar

Rebecca... did you even look at my post #2? You don't need more variables... You can do the conversion right in the printf() statement and then you can discard the line I commented out entirely.

Also... In your place I would speak to my professor... "Hey teach, I found this and a bunch of guys on the forum confirmed that fflush(stdin) is a bad thing to do... Since working programmers don't use it, we should not be losing points over it." .... People are basically lazy, habit driven creatures... change does not come without cause.

Originally Posted by CommonTater

Rebecca... did you even look at my post #2? You don't need more variables... You can do the conversion right in the printf() statement and then you can discard the line I commented out entirely.

yes, i did see that BUT it's another thing my professor said we shouldn't do. he did state equations in printf statements are valid, but he doesn't want us to use them.....

so i guess it's another reason for you to hate my professor haha

Originally Posted by Rebecca Bombard

yes, i did see that BUT it's another thing my professor said we shouldn't do. he did state equations in printf statements are valid, but he doesn't want us to use them.....

so i guess it's another reason for you to hate my professor haha

Well, I do have to admit I'm starting to think he's something of an idiot...

When you don't need to keep the result, assigning it to a variable is just plain silly.

I think I've just found my retirement hobby.
Sign up for intro C programming courses around the country, then rip 'em a new one whenever the tutor starts spouting nonsense.

Originally Posted by Salem

I think I've just found my retirement hobby.
Sign up for intro C programming courses around the country, then rip 'em a new one whenever the tutor starts spouting nonsense.

Good lord man... come this way first, my bags are already packed!

Really... some of the stuff I've seen here just makes me want to scream...

Remember that kid last winter who swore up and down he was in a C course but his teacher kept giving them C++ code...

Originally Posted by Rebecca Bombard

no, he suggests we use C free but doesn't require a specific complier. i looked at my syllabus and it states -2 points for anytime fflush (stdin) is not used.

Yet another reason why I am glad I was not a CS major. The equivalent in my field would be for the prof to demand Newtonian physics be applied at the quantum level. Seriously, why is CS such a mis-represented topic?

Originally Posted by AndrewHunter

Yet another reason why I am glad I was not a CS major. The equivalent in my field would be for the prof to demand Newtonian physics be applied at the quantum level. Seriously, why is CS such a mis-represented topic?

Times like this I am so glad I'm self-educated... the crap some of these schools teach is beyond disheartening.

"Here I want you to use this code even though it orphans varaibles and relies upon undefined behavior"... Yeah, that'll work...

Code:

#include <stdio.h>


int main (void)
{
    /*Variable declarations*/
    float usdollar = 0, krones = 0, euros = 0, hkdollars = 0, total = 0;
    int us_conversion = 3, i;
    
        /*Welcome and program description*/
    printf("Welcome to the Bombard Money Exchange\n\n");
    printf("The program will convert three US dollar amounts to Danish Krones, Euros and Hong Kong Dollars.\n\n");
    
    /*User enters exchange rates*/
    printf("First, Please enter the exchange rates:\n");    

    printf("Danish Krones: ");
    scanf("%f", &krones);     

    printf("Euros: ");
    scanf("%f", &euros);    

    printf("Hong Kong Dollars: ");
    scanf("%f", &hkdollars);     
    
    printf("\n\nEnter US Dollars to be converted: ", i);
    scanf("%f", &usdollar);
   
    printf("\n%.2f US dollars is equivelent to:\n\n ", usdollar);
    printf("\t%.2f Danish Krones\n", krones * usdollar);
    printf("\t%.2f Euros\n", euros * usdollar);
    printf("\t%.2f Hong Kong Dollars\n", hkdollars * usdollar);
 
    return 0;
}