A number of us use the C18 compiler. I think at least one person is using the C24.

They work.

3v0

The two pages you provided seem to outline the features of each; I would suggest looking at that.

Originally Posted by MPLAB C Compiler for Academic Use

Features
Key features of the MPLAB C Compiler for Academic Use (LITE) include:

* ANSI-compliant
* Free, fully functional, with all libraries and source code as commercial versions
* Integrated with MPLAB IDE for easy-to-use project management and source-level debugging
* Generates relocatable object modules for enhanced code reuse
* Fully compatible with object modules generated with MPASM Assembler, allowing complete freedom to mix assembly and C in a single project
* Interrupt code can be written in C or assembly
* Flexible memory models take advantage of small memory applications and the storage of data in SFR space
* Strong support for inline assembly when total control is absolutely necessary
* Super-efficient code generator engine with multi-level optimization
* Extensive library support, including standard C, math, DSP and peripheral libraries
* Additional software libraries and application development tools are available from Microchip’s web site
* GNU-based, open source code (except PIC18)

Originally Posted by MPLAB C Compilers

Microchip Compiler Features:

* ANSI compliant, with standard math, memory, data conversion and math libraries
* Generates relocatable object modules and libraries for enhanced code reuse.
* Optimized to generate as much as 30% less code than other commercial compilers
* Strong support for in-line assembly when total control is absolutely necessary
* Allows complete freedom to mix C and assembler modules in a single project
* Extensive libraries including Microchip peripheral libraries
* Multiple optimization levels
* Full user control over data and code memory allocation
* Full interrupt support
* Free Evaluation Versions (below)
* Free upgrades
* Download free unrestricted use student editions and the free MPLAB IDE at Microchip Technology Inc. - a Leading Provider of Microcontroller and Analog Semiconductors

Originally Posted by HATHA

ok, is that mean C Compiler for Academic Use doesn't have code optimazation as in as commercial versions. mean same code written in two compiler take different space in code memeory ?

After the trial expires yes.

If you're writing mega code for commercial use then buy the compiler. That's the idea behind a student edition.

The C18 is not open-source I think the rest are