Xcode - Warning Implicit declaration of function is invalid in C99

Question

Getting a warning   Implicit declaration of function  Fibonacci  is invalid in C99  What s wrong    include  lt stdio h gt   int main int argc  const char   argv          int input      printf  Please give me a number           scanf   d    amp input       getchar        printf  The fibonacci number of  d is    d   input  Fibonacci input               main     int Fibonacci int number        if number lt  1           return number       else          int F   0          int VV   0          int V   1          for  int I 2  I lt  getal  I                  F   VV V              VV   V              V   F                    return F           Fibonacci

User · Answer

should call the function properly  like- Fibonacci input

User · Answer

The function has to be declared before it s getting called  This could be done in various ways    Write down the prototype in a header Use this if the function shall be callable from several source files  Just write your prototype int Fibonacci int number   down in a  h file  e g  myfunctions h  and then  include  myfunctions h  in the C code  Move the function before it s getting called the first time This means  write down the function int Fibonacci int number      before your main   function Explicitly declare the function before it s getting called the first time This is the combination of the above flavors  type the prototype of the function in the C file before your main   function   As an additional note  if the function int Fibonacci int number  shall only be used in the file where it s implemented  it shall be declared static  so that it s only visible in that translation unit

User · Answer

The compiler wants to know the function before it can use it  just declare the function before you call it   include  lt stdio h gt   int Fibonacci int number     now the compiler knows  what the signature looks like  this is all it needs for now  int main int argc  const char   argv          int input      printf  Please give me a number           scanf   d    amp input       getchar        printf  The fibonacci number of  d is    d   input  Fibonacci input               main     int Fibonacci int number

User · Answer

I have the same warning  it s make my app cannot build   When I add C function in Objective-C s  m file  But forgot to declared it at  h file

[c] Xcode - Warning: Implicit declaration of function is invalid in C99

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