Currency conversion program

[Just starting out]

I am very new to C code and I'm having a lot of trouble with a homework
assignment.

This program is supposed to take the amount of Euros that the user
enters and convert it to US dollars.

It runs fine if the user enters a number, but if the user enters a
letter it loops.

I have been working on this for 3 hours now, trying different things
left and right. I'm sure it has something to do with the isdigit
function. So, I tried adding in a char cResponse and switching the
value to fResponse after checking for a number.

I am fried, please help!

---------------------------------------

#include <stdio.h>
#include <system.h>
#include <ctype.h>

main ()

{

//set variables
float fUSD, fEUR, fResponse;

//initialize variables
fUSD = 0;
fEUR = 0;
fResponse = 0;

//set values
fUSD = 1.00;
fEUR = .7435;
//print headers for output screen
printf("\n***Cu rrency Conversion***\n ");
printf("\nConve rts Euro into US dollar\n");
printf("\nPleas e enter the amount in Euro: ");

//get user input
scanf("%f", &fResponse);

//check for number greater than zero
while (fResponse<=0.0 ) {
if (isdigit(fRespo nse)) {
printf("\nThe number you entered is invald.\n");
printf("Please enter a number larger than zero: ");
scanf("%f", &fResponse);
}
if (isdigit(fRespo nse)==0)
printf("\nYou entered a letter.\n");
printf("Please enter a number larger than zero: ");
scanf("%f", &fResponse);

}

printf("\nThe value of the Euro you entered converts to $%.2f US
dollars.\n", (fUSD/fEUR) * fResponse);

printf("\n\nPre ss any key to close this window. . .");

//getch function to leave results on screen until any key is chosen
getch ();

}

[Flash Gordon]

Just starting out wrote:

Flash,

Thanks for your feedback!
Provide context otherwise we can't see what you are replying to. I, for
one, don't bother to remember every single post I make to news groups
and have my reader configured to only show unread posts. Others might
not have even seen my post. Check any post by CBFalconer and read his
sig for instructions on how to work around the crappy interface Google
provide.
I'm using Miracle C compiler for my assignments.
Irrelevant.
I'm not sure what you mean by ending the printf statement with a new
line or flush stdout. I wanted the user input to appear at the end of
the "Please enter a number: " line. I checked my book for flush stdout
and it looks like I need a new book.
You use
fflush(stdout);
to flush the output. If you don't then the C language does not guarantee
that the message will actually be displayed before the user presses
return when entering data. It's called line buffering.
I replaced my original scanf with the "while(scanf... " code that
kernelxu suggested. The two printf lines both print according to the
number of letters the user enters. (ex. user enters STOP, the printf
lines both print 4 times).
If I recall correctly I posted comments about the problems with his
code. Read up on how scanf works. Of course, since you have not posted
or quoted the code I can't see to tell you the specific problems.
Our class was told to use getch(); function in order to keep the window
from automatically closing. Maybe it's a Miracle C thing.

It may well be, but it is not part of the C language.
--
Flash Gordon
Living in interesting times.
Although my email address says spam, it is real and I read it.

[Peter Nilsson]

Flash Gordon wrote:

Just starting out wrote:

...
I'm not sure what you mean by ending the printf statement with a
new line or flush stdout. I wanted the user input to appear at the
end of the "Please enter a number: " line. I checked my book for
flush stdout and it looks like I need a new book.
You use
fflush(stdout);
to flush the output. If you don't then the C language does not
guarantee that the message will actually be displayed before the
user presses return when entering data.

Even using fflush(stdout), the C language won't make that guarantee.
[Try redirecting stdout to an old line buffered printer one day.]
It's called line buffering.

Indeed. Whilst the _stream_ can be flushed, there's no guarantee
that the 'display device' won't have it's own buffering. Using
fflush() will work for 99.999% of consoles, but for the maximum
chance of the prompt appearing, it should end with a newline.

i.e. use...

puts("Enter an integer:");

....over...

printf("Enter an integer: ");
fflush(stdout);

Our class was told to use getch(); function in order to keep the
window from automatically closing. Maybe it's a Miracle C thing.

No, it's largely a windoze thing. Nonetheless, there are better
options,
although that discussion is off-topic in clc.

--
Peter

[Keith Thompson]

"Peter Nilsson" <ai***@acay.com .au> writes:
[...]

Indeed. Whilst the _stream_ can be flushed, there's no guarantee
that the 'display device' won't have it's own buffering. Using
fflush() will work for 99.999% of consoles, but for the maximum
chance of the prompt appearing, it should end with a newline.

i.e. use...

puts("Enter an integer:");

...over...

printf("Enter an integer: ");
fflush(stdout);

As much as I'm a fanatic for portable code, I don't agree. Printing a
prompt without a newline makes for a much friendlier interactive
program. On a system where the printf/fflush form doesn't work, I
wouldn't be sure that prompting would work at all.

--
Keith Thompson (The_Other_Keit h) ks***@mib.org <http://www.ghoti.net/~kst>
San Diego Supercomputer Center <*> <http://users.sdsc.edu/~kst>
We must do something. This is something. Therefore, we must do this.

[Keith Thompson]

Barry Schwarz <sc******@deloz .net> writes:
[...]

You have to provide some context. What code are you talking about.
The fact that the google interface is broken means you have to do it
manually.

No, you don't have to do it manually. All you have to do is (all
together now):

If you want to post a followup via groups.google.c om, don't use
the broken "Reply" link at the bottom of the article. Click on
"show options" at the top of the article, then click on the
"Reply" at the bottom of the article headers.

and it will quote the previous article and fill in proper
attributions.

Google's unforgivable blunder is, first, putting this in a hidden menu
rather than making it the default, and second, not fixing it to this
day.

--
Keith Thompson (The_Other_Keit h) ks***@mib.org <http://www.ghoti.net/~kst>
San Diego Supercomputer Center <*> <http://users.sdsc.edu/~kst>
We must do something. This is something. Therefore, we must do this.

[Gordon Burditt]

>> Indeed. Whilst the _stream_ can be flushed, there's no guarantee

that the 'display device' won't have it's own buffering. Using
fflush() will work for 99.999% of consoles, but for the maximum
chance of the prompt appearing, it should end with a newline.

i.e. use...

puts("Enter an integer:");

...over...

printf("Enter an integer: ");
fflush(stdout);

As much as I'm a fanatic for portable code, I don't agree. Printing a
prompt without a newline makes for a much friendlier interactive
program. On a system where the printf/fflush form doesn't work, I
wouldn't be sure that prompting would work at all.

For whatever it's worth, there are hardcopy printers, some with
keyboards, that don't print anything but whole lines. The prompt
wouldn't appear as ink on paper until after you'd answered it. There
are others where the prompt is printed but the printhead is in
the way until the paper has advanced.

Gordon L. Burditt