title: Xcode - Warning: Implicit declaration of function is invalid in C99
body: <p>Getting a warning : Implicit declaration of function 'Fibonacci' is invalid in C99.
  What's wrong?</p>
  
  <pre><code>#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*/
  </code></pre>