title: Implicit declaration
body: <p>I am using Xcode 4.1 on Mac OS 10.7</p>
  
  <pre><code>#include &lt;stdio.h&gt;
  
  int main (int argc, const char * argv[])
  {
      int i, j;
  
      i = 1;
      j = 9;
      printf("i = %d and j = %d\n", i, j);
  
      swap(&amp;i, &amp;j);
      printf("\nnow i = %d and j = %d\n", i, j);
  
      return 0;
  }
  
  swap(i, j)
  int *i, *j;
  {
      int temp = *i;
      *i = *j;
      *j = temp;
  }
  </code></pre>
  
  <p>I get the warning "Implicit declaration of function "swap" is invalid in C99</p>