The example you posted runs like a charm on my system. No compiler errors or warnings. Ensure you saved the file as .c file, not as .wdl file. Additionally have a look if this script is really the one that won't compile. You can press Alt + F5 to make the current script the one that is taken as the main script.

Other than that your program won't do anything sensefull. As you declared a,b and c as zero the numbers will never change at all.