Here are examples showing how you might (1) coalesce two similar functions using a "mode" flag, (2) break the common code out to a third function, and (3) make one function a proper subset of another, by having one function call the other.

• (1) If you have two functions which are almost identical except for one little difference in the middle, like this:

  function_1()                    	function_2()
  {                               	{
  common statement 1;             	common statement 1;
  common statement 2;             	common statement 2;
  different statement 3;          	different statement 4;
  common statement 5;             	common statement 5;
  common statement 6;             	common statement 6;
  }                               	}
  

  sometimes it's appropriate to coalesce the two functions, adding a "mode" flag telling it which of the two options to perform:

  combined_function(int flag)
  {
  common statement 1;
  common statement 2;
  if(flag)
  	different statement 3;
  else	different statement 4;
  common statement 5;
  common statement 6;
  }
  

• (2) If you have two functions where the common code is all together, with the differences around the edges, like this:

  function_1()                        function_2()
  {                                   {
  different statement 1;              different statement 2;
  common statement 3;                 common statement 3;
  common statement 4;                 common statement 4;
  common statement 5;                 common statement 5;
  different statement 6;              different statement 7;
  }                                   }
  

  you can often break the common code out to a third function, like this:

  function_1()
  {
  different statement 1;
  function_3();
  different statement 6;
  }
  
  function_2()
  {
  different statement 2;
  function_3();
  different statement 7;
  }
  
  function_3()
  {
  common statement 3;
  common statement 4;
  common statement 5;
  }
  

• (3) Finally, if one function is a subset of another, like this:

  little_function(int a, int b)        big_function(int a, int b, int c)
  {                                   {
  common statement 1;                 common statement 1;
  common statement 2;                 common statement 2;
  common statement 3;                 common statement 3;
  }                                   different statement 4;
                                      different statement 5;
                                      }
  

  you can often have one function call the other. Sometimes it will look like this:

  little_function(int a, int b)
  {
  common statement 1;
  common statement 2;
  common statement 3;
  }
  
  big_function(int a, int b, int c)
  {
  little_function(a, b);
  different statement 4;
  different statement 5;
  }
  

  Or, sometimes, the extra code in the "big" function applies only if the extra parameter takes on some non-default value. In that case, sometimes you can make the little function a "wrapper" around the big one:

  little_function(int a, int b)
  {
  big_function(a, b, default_value);
  }
  
  big_function(int a, int b, int c)
  {
  common statement 1;
  common statement 2;
  common statement 3;
  if(c != default_value)
  	{
  	different statement 4;
  	different statement 5;
  	}
  }