title: Why are all cout's and cin's "undeclared identifiers
body: <p>In my main.cpp all of my cout's and cin's have errors.</p>
  
  <pre><code>/**
  * Description: This program demonstrates a very basic String class.  It creates
  * a few String objects and sends messages to (i.e., calls methods on)
  * those objects.
  *
  */
  //#include &lt;iostream&gt;
  #include "mystring.h"
  //using namespace std;
  
  /* Function Prototypes */
  
  void Display(const String &amp;str1, const String &amp;str2, const String &amp;str3);
  
  
  /*************************** Main Program **************************/
  
  int main()
  {
    String str1, str2, str3;   // Some string objects.
    char s[100];               // Used for input.
  
    // Print out their initial values...
  
   cout &lt;&lt; "Initial values:" &lt;&lt; endl;
   Display(str1, str2, str3);
  </code></pre>
  
  <p>My main.cpp cannot not be changed, so my question is, how can I fix this error, what do I have to add to my header file and implementation file?</p>