I know that arduino language is based on C language,and the avr controller.
but i don't know the exactly difference between arduino language and C language.
for example, digitalwrite() in arduino language can be replaced by C language,
are there any place to find this kind of reference?
my background:
I am a teacher,my most students said C language is hard to learn and lost interests?
So I want to use arduino language to draw students to learn something, then to make them interesting on programming?
Thanks!
The Arduino language is C/C++
Things like digitalWrite() are just special functions designed to make life easier. The C/C++ code that implements those functions is included in the files that come with the Arduino IDE.
...R
Did you read this?
http://forum.arduino.cc/index.php?topic=97455.0
The Arduino IDE uses C++.
You can add C files to your project if you want to.
I am a teacher,my most students said C language is hard to learn and lost interests.
Oh? Well you'll have to show them how easy it is to achieve remarkable things with the Arduino.
Maybe start them off with this:
http://forum.arduino.cc/index.php?topic=197983.0
Of course that isn't a beginner project, but it gives you an incentive to learn. 
Project page: Toorum's Quest II - ATmega328P based retro video game with 256 color graphics - Exhibition / Gallery - Arduino Forum
yes, i found the .c file and .h file coming with the IDE, and the all function definition.
Thanks!