Yes: you can use VC# to create a Step7 source (text) file. In other words you can develop a CASE tool that writes S7 source code for you. To compile S7 source code you must use the Siemens Step7 editor.
No: Step7 instruction set is proprietary, you cannot write straight C code. Within Step7, the only thing close to an high-level language is SCL, provided as add-on package. It provides a rather limited number of instructions.
In any case you do need Step7 programming package.
Also, SCL doesn't really work like C because you have to write it so that there are no loops waiting on IO or anything or else you'll blow the watchdog timer, etc. I originally thought you could program SCL (A Pascal-like language) like you would in C++, but it doesn't really work that way. Having said that, it works OK for data processing tasks.
