newbie help with "if" and "char"

**morgog** · 02-23-2009

Hi,
I am very new to C, so I apologise if this is a really stupid question.
I'm trying to read a character input from the keyboard (F or C) and if the response is F calculate from Fahrenheit to Celcius, else calculate from Celcius to Fahrenheit.
But I keep getting an error (using Visual Studio 2005)

Code:

error C2065: 'f' : undeclared identifier

Is the problem something to do with char/string cannot use = or == ... or am I missing something simple.
Any help appreciated.

Code:

#include <stdio.h>


void main()

{
	float degEntered;
	float degC;
	float degF;
	char Conversion;

	printf("Please enter the temperature: ");
	scanf("%f%*c",degEntered);
	printf("F to C (enter f) or C to F (enter c): ");
	scanf("%c%*c",Conversion);

	if (Conversion == f)
	{
		degC = (degEntered - 32) / 1.8;
		printf("It is %5.2f degrees C",degC);
	}
	else
	{
		degF = 1.8 * degEntered + 32;
		printf("It is %5.2f degrees F",degF);
	}
scanf("%*c");
}

**ganesh bala** · 02-23-2009

f should b in single quote as it is a char...

use int main .. dont use void main..

**morgog** · 02-23-2009

Thanks for the quick help with the problem.

I only noticed after reading your reply that :

Code:

scanf("%f%*c",degEntered);
..
and

scanf("%c%*c",Conversion);

should be:

Code:

scanf("%f%*c",&degEntered);
scanf("%c%*c",&Conversion);

But the main thing is that the program now compiles & returns the correct result.

Thanks again!!

**Elysia** · 02-23-2009

void main()
INCORRECT.

int main()
CORRECT.

**san_crazy** · 02-23-2009

hi morgog,

I have designed a website to make understand new comers like you the C/C++ programming language in depth. its totally different from other tutorials YOU might have found somewhere across the internet.

the contents are being added daily and very soon you will get the complete tutorial.

check this out and understand concept of C/C++ very easily.

http://www.stripathi.110mb.com/Tutor..._contents.html

**Elysia** · 02-23-2009

The link is broken.

**san_crazy** · 02-23-2009

check that again

**Elysia** · 02-23-2009

Perhaps you better check over that tutorial again. When you see something like this...

The remaining two will be stored somewhere else as fixed locations are not given for these.

...for scanf, then you know something is wrong.
You MUST explicitly specify where to store ALL the arguments you ask for. If not, you are invoking undefined behavior.

The same for printf. It's undefined.
Sorry, I do NOT trust that site.

**san_crazy** · 02-23-2009

Originally Posted by Elysia

Perhaps you better check over that tutorial again. When you see something like this...

...for scanf, then you know something is wrong.
You MUST explicitly specify where to store ALL the arguments you ask for. If not, you are invoking undefined behavior.

The same for printf. It's undefined.
Sorry, I do NOT trust that site.

hi elysia,

I think you have misunderstood the things

I have just given a case if a user dont give the locations for all the arguments then what may be happen

if he write

Code:

   scanf("%d %c %f",&a);

its not an error, since here also user must have to enter three values from keyboard(although its not given where to store other two values) hence scanf can store remaining two anywhere else.

how many value scanf() will read depends on the format specifiers .

**Elysia** · 02-23-2009

I have not misunderstood. This is undefined.
Since you tell scanf to read 3 values, so it will. And it needs a place to store those. It will not store them "somewhere else". It will try to read some arguments you, the programmer, should have passed but have not, and likely crash.
Did you try this?

**laserlight** · 02-23-2009

Originally Posted by san_crazy

its not an error, since here also user must have to enter three values from keyboard(although locations for two values are not given) hence scanf can store remaining two anywhere else.

No, the C standard states very clearly: "If there are insufficient arguments for the format, the behavior is undefined."

So, you can validly argue that it is not an error, but likewise the compiler author can validly argue that there is no bug in the compiler even though the program generated by the compiler happens to do something unexpected like attempt to erase as many of your files as it can.

**san_crazy** · 02-23-2009

well.....i have tried it many times in turbo c compiler and didn't get anything you have stated

**Elysia** · 02-23-2009

Turbo C... of course.
That gives me another reason not to trust the site.
Try an up-to-date compiler, such as Visual Studio or GCC, and then try again.

**laserlight** · 02-23-2009

Originally Posted by san_crazy

well.....i have tried it many times in turbo c compiler and didn't get anything you have stated

Since the behaviour is undefined, your compiler can do anything, including whatever you expect.

**Salem** · 02-23-2009

Ah, the good old "I've got a test case which 'works for me', therefore my argument is proven".

Bzzzt - wrong. Try some other operating systems and compilers (especially ones like GCC which warn you about making a mess of printf/scanf calls).

Sooner or later, you'll get your ass handed to you on a plate in the form of a segmentation fault (or worse).

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