Thread: Cannot figure out this bug "error: conflicting types"

  1. #1
    Registered User
    Join Date
    Apr 2011

    Cannot figure out this bug "error: conflicting types"


    I am trying to work on a "simple" problem from K&R book. The excercise is as under:

    Rewrite the temperature conversion program of Section 1.2 to use a function for conversion.
    My attempt:
    #include <stdio.h>
    #include <stdlib.h>
     int main(void) {
    	float fahr;
    	float collector;
    	int lower = 0;
    	int upper = 300;
    	int step = 20;
    	fahr = lower;
    	while (fahr <= upper)
    		collector = FtoC (fahr); 
    		printf ("\n F is %3.0f & C is %6.1f", fahr, collector);
    		fahr = fahr + step;
    	return 0;
    float FtoC (float n)
    	float c;
    	c = (5.0 / 9.0) * (n - 32.0);
    	return c;
    As far as my knowledge goes, there isn't any bug in this code but compiler is returning this error & warning. I've no idea WHY? Kindly help.

    /src/celsius_converter.c: In function ‘main’:
    ../src/celsius_converter.c:23:3: warning: implicit declaration of function ‘FtoC’ [-Wimplicit-function-declaration]
    ../src/celsius_converter.c: At top level:
    ../src/celsius_converter.c:30:7: error: conflicting types for ‘FtoC’
    ../src/celsius_converter.c:23:15: note: previous implicit declaration of ‘FtoC’ was here
    make: *** [src/celsius_converter.o] Error 1

  2. #2
    Registered User
    Join Date
    Aug 2005
    you have to forward declare FtoC();

    float FtoC (float n);
    before main().

    otherwise the compiler thinks FtoC is a function that returns int.


  3. #3
    Registered User
    Join Date
    Mar 2011
    Yes the above reply is correct. On a more general level, u need to either define the function before you use it or declare it before using it in main and define it after main.
    Last edited by livin; 08-27-2012 at 04:22 PM.

  4. #4
    Registered User
    Join Date
    Apr 2011
    Thanks! That helped & thanks for giving reasons behind it too.

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