Not eXactly C is a high-level programming language for the Lego Mindstorms NXT. NXC, which is short for Not eXactly C, is based on Next Byte Codes, an assembly language. NXC has a syntax like C.
There is a new version of the NXC Tutorial available at the Roberta Homepage. It is an extended german version of the tutorial original based on the work of Daniele Benedettelli.
You can download the german tutorial for free here: http://roberta-home.de/de/was-bietet-roberta/roberta-reihe/nxc-tutorial
The English original version is available here: http://bricxcc.sourceforge.net/nbc/nxcdoc/NXC_tutorial.pdf