title: What does '#include <stdio.h>' really do in a C program
body: <p>I am  new to c programming and I was coding some simple programs "Hello world" style. </p>
  
  <p>In all of these programs I put <code>#include&lt;stdio.h&gt;</code> in the top but I am not sure what this means exactly. I googled it and I found that stdio.h is a file that has commands for the preprocessor, but what is a preprocessor? I thought when I write code, I compile it and my code transforms to a form that a "computer" can read and then I can run it. Can somebody explain to me what the usage of this command is?</p>