For instance, let's say I have two images preferably jpeg/bmp that are 128x128 - I would like the code to stitch them together so the resulting image is 256x128.
I want a c++ program for it..is it possible using files in c++.
Reading BMP files is easy. They're little more than a dump of the pixels.
Start simple - write a program which just prints out the width and height of any BMP file you give it.
> but are you sure that a graphics library would be needed
For JPG yes.
If you want to decode JPG from scratch, you need a lot more experience, probably university level maths and a lot of time to spare.
I might suggest you get a compiler that isn't older than you are. TC effectively became obsolete 20 years ago.