Sin/Cos calculator is a mathematical comand-line calculator.
I was chatting to this guy on IRC who was moaning about his homework. trying to write a program to do this in bash. I said you'd be much better off doing it in C, and wrote this. Gave it to him the next day after they'd finished the chapter.
As it does both, there's two executables, it builds main() depending on preprocessor definition... more in the source file.
gcc -lm sin_rule.c -ansi -pedantic -DSINE_RULE -o sin-rule