Logical Error - convert Fah to Celsius

Question

#include <stdio.h>
#define F(x) 32 + (x*9)/5

int main(void)
{ 
  int F,C;
  printf ("Enter temperature in celsius=");
  scanf ("%d",&C);
  F(C);

  printf (" %d fahrenheit = %d celsius\n", F, C);

  return 0;
 }

When I input 10 celsius, it comes out some as:

1798680630 fahrenheit = 10 celsius

Am I writing the formula wrongly? I can't seem to figure out the error. Just a beginner, going through my tutorials. Thank you!

You forgot to add a `F=` in front of `F(C)`, because you want to assign the value to your variable `F`. http://ideone.com/Xc6c3x — mch, Oct 04 '16 at 14:11
[Why confuse people?](https://blog.codinghorror.com/coding-for-violent-psychopaths/) — Sourav Ghosh, Oct 04 '16 at 14:12
First of all, given that these are ints, you might lose too much information while dividing. Secondly, you shouldn't (can't) have both a variable F and a macro F, it's bound to have errors. See the answers below about why your code doesn't work — neoaggelos, Oct 04 '16 at 14:13

score 2 · Answer 1 · answered Oct 04 '16 at 14:12

2

You are not storing the result of the macro expansion at all. So, F is uninitilized.

IMO, the macro isn't needed at all. Just use a variable:

#include <stdio.h>
int main(void)
{
  int C;
  float F;
  printf ("Enter temperature in celsius=");
  scanf ("%d",&C);
  F = 32 + (C*9)/5.0;
  printf (" %f fahrenheit = %d celsius\n", F, C);

  return 0;
 }

Notice that I used the literal 5.0 so that you don't perform just integer division.

answered Oct 04 '16 at 14:12

P.P

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thank you! i changed it to macro as the simpler one didnt give me the right output. ill try again. – belle Oct 04 '16 at 15:07

score 0 · Answer 2 · answered Oct 04 '16 at 14:11

0

You don't save output of F() to a variable. It should be:

  (...)
  F = F(C);

  printf (" %d fahrenheit = %d celsius\n", F, C);

Currently you are printing an uninitialized variable which is undefined behavior and is quite dangerous.

answered Oct 04 '16 at 14:11

Arkadiusz Drabczyk

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score 0 · Answer 3 · answered Oct 04 '16 at 14:17

0

You are printing the address of the F. Also do not waste variables.

Remove

F(C);

Do your printing like :

printf (" %d fahrenheit = %d celsius\n", F(C), C);

answered Oct 04 '16 at 14:17

cagdas

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Logical Error - convert Fah to Celsius

3 Answers3