Propeller: SPIN, C, C++, GCC. Future of Spin Tool vs. SimpleIDE?

I'm unsure of differences in languages listed. When should I use C vs C++? Why Spin over C?

I've used Spin Tool and Simple IDE. Seems last few years was examples in SPin Tool and now are in Simple What of above will continue to be supported? (Will Simple IDE evolve to handle SPIN and then Spin Tool die?)