C is also supported by Casio itself on Classpad 3G but for other models you have to stick with BASIC. Also the only calcs with ASM support are Casio AFX and I think 9860G. Also I heard that these models execute BASIC language even slower than CFX models (the ones with color screen). Also the AFX models breaks after only a few years, because the flash memory (I think it's 768KB) lifetime is very short compared to the Casio FX-9860G and TI models. The slower processors (4 MHz I think) doesn't help much though.
But even then the language is still much slower. However on 2nd generation BASIC models it takes about 1/8 seconds for each character to appear, one by one, so if you want to disp text you better use Locate (which is the equivalent of Output, which is signifiantly slower). Some commands are at decent speed, but for example if you want to do Disp 'HELLO WORLD', on Casios you simply do 'HELLO WORLD', that's all. The commands are basically the same it seems on most calcs, even the cheap FX-9750G, but the Casio BASIC language is extremly slow compared to TI-BASIC. IMHO, before the FX-9860G models came out Casio graphing calcs were inferior to TIs programming wise.
