Figure 1: Typical use (and abuse) of error codes

// ErrorCodes.h
enum ErrorCode 
{ Success, MyError1, MyError2, MyError3 };

// main.cpp
#include "ErrorCodes.h"

ErrorCode doSomeJob(int _i)
{
   if (_i == 0)
      return MyError1;
   else if (_i > 10)
      return MyError2;
  
   ... // some code

   return Success;
}

ErrorCode myFunc(void)
{
   doSomeJob(0); // <-- return value not used

   ErrorCode err = doSomeJob(5);
   err = doSomeJob(15); // <-- previous value 
                        // of err not tested
   if (err != Success)  // <-- return value
      return err;       // is tested
  
   ... // some code
  
   return Success;
}

int main(void)
{
   if (myFunc() == Success)
      return 0;
   else
      return 1;
}