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 · Accepted 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

should call the function properly  like- Fibonacci input

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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