Parts of the labs require you to write C code using the Eclipse IDE. The similarity of syntax between C and Java means you should have little difficulty in using the C language for the given tasks.
The following outlines a few facts about the standard C language. A more thorough overview is given in the lecture course Programming in C and C++.
Note that, unlike Java, there are many popular C compilers and each has its quirks; your code should not depend on your choice of compiler. If in doubt, refer to the official documentation. The labs direct you to use the compiler available in Eclipse, which produces machine code for the NIOS II processor.
C is an imperative, monolithic programming language; a C program may span multiple (specified) files and is logically a set of procedures and constants. Before a program is compiled (in the usual sense), it is passed through the C preprocessor: preprocessor macros are separate from the main language, and result in textual manipulation of the source file:
A source file in C has the extension .c. Header files (.h) are often used to separate preprocessor macros from the source code.
In general, you should assume language constructs behave as for Java. The following outline some important differences.