Any way to include the text of a file inside a sketch, to make it shorter and neater? I'm wondering if there is any way to include the text of a file into a sketch by using a single placeholder command, similar to the "#Include" command when using Server Side Includes on .shtml files.

I'm sorry if I'm not wording this correctly. It was hard for me to phrase it and also hard for me to search about it, since the nouns seem so generic.

I understand that some parts of code can be separated out into their own functions, and that those functions could be saved in a different .ino file. But I'm wondering about for the cases that can't be separated out into functions (like for declarations at the beginning of a sketch, or an area in loop() that would require too many variables to be passed to the function).



EDIT: I think I should've been more specific:
In one example, I have lots of html code being served from the loop() function. The Arduino webserver is serving a complex page that shows about 100 buttons on the webpage. I would like to separate the page-serving code to a separate .ino file and have it opened as a separate tab in the Arduino IDE. That way it's easy for me to open that tab whenever I want to modify the webpage, but also the code for serving the page won't take up so much space in my main file. The code isn't completely html (it has lots of functions and conditionals), so that's why I can't just save it as an external .html file and have it served from that file.

As another example: At the top of my sketch I have lots of defines for wireless signals that need to be sent. They look like this:

const unsigned long a1o = 4216115, a1c = 4216124, a2o = 4216259, a2c = 4216268, a3o = 4216579, a3c = 4216588, a4o = 4218115, a4c = 4218124, a5o = 4224259, a5c = 4224268; //remote control 1


There are 10 lines of code that look like that, and I never have to modify them because they're all constants. When I'm searching for bugs in my code, I never have to refer to those lines, and they're usually just in my way.
As suggested in comments, you can use #include statements to include texts of files into a sketch.  For example, suppose files c1.h,  c2.h,  c3.h,  c4.h, and  c5.h are in directory ~/sketchbook/tincludes, along with the file tincludes.ino, which is as follows:

#include &lt;Streaming.h&gt;
void setup() {
  const long int
#include "c1.h"
#include "c2.h"
#include "c3.h"
#include "c4.h"
#include "c5.h"
 etc=5   ;
  Serial.begin(115200);
  Serial &lt;&lt; z1o &lt;&lt;  z1c &lt;&lt;  z2o &lt;&lt;  z2c &lt;&lt;  z3o &lt;&lt;  z3c &lt;&lt;  z4o &lt;&lt;  z4c &lt;&lt;  z5o &lt;&lt;  z5c;
}


Further, suppose c1.h ... c5.h each contain one line of code, as follows:

==&gt; c1.h &lt;==
  z1o=25829, z1c=9774,

==&gt; c2.h &lt;==
  z2o=7850, z2c=25585,

==&gt; c3.h &lt;==
  z3o=7103, z3c=17981,

==&gt; c4.h &lt;==
  z4o=30827, z4c=24511,

==&gt; c5.h &lt;==
  z5o=4167, z5c=10036,


Then the sketch will compile ok, and the sketch-lines with const long int through etc=5   ; will compile the same as if they were replaced by 

const long int z1o=25829, z1c=9774, z2o=7850, z2c=25585, z3o=7103,
     z3c=17981, z4o=30827, z4c=24511, z5o=4167, z5c=10036, etc=5;