i read the code of the Lesson One,and some of his wirting confused me. Listed below,can anyone give me answers? 1 Line 81: hRC=NULL; why dont wirte this without some those two IF sentence? 2 Line 124 & 129: why dont use 'wc.hIsntance=hIsntance' without 'GetModuleHandle(NULL)'? 3 Line 126: how about use the 'wc.lpfnWndProc = WndProc' instead of 'wc.lpfnWndProc = (WNDPROC) WndProc' 4 Line 125: without setting 'CS_OWNDC'? 5 Line 184: is there any differencs between the 'CreateWindowEx' & 'CreateWindow' the last one is how can i get some explains of the OpenGL's variable type,such as GLvoid

I don't use OpenGL, but I'll try to answer your questions:

Quote: 1 Line 81: hRC=NULL;
why dont wirte this without some those two IF sentence?

Could you rephrase that? I dont understand your question. The two previous if statements will not prevent hRC from being set to NULL.

Quote: 2 Line 124 & 129:
why dont use 'wc.hIsntance=hIsntance' without 'GetModuleHandle(NULL)'?

Because you would need to either pass the instance via a parameter, or have it global. I guess the former is a hassle, from the point of view of the author. The latter is rarely a good idea.

Quote: 3 Line 126:
how about use the 'wc.lpfnWndProc = WndProc' instead of 'wc.lpfnWndProc = (WNDPROC) WndProc'

There's no need to cast it, it's already of the correct form. Note that in C++, you can assign a free-function pointer with or without the address-of operator.

Quote: 4 Line 125:
without setting 'CS_OWNDC'?

I am no sure why exactly it is used, but perhaps it has to do with how OpenGL deals with device contexes in Windows.

Quote: 5 Line 184:
is there any differencs between the 'CreateWindowEx' & 'CreateWindow'

Yes. CreateWindowEx() allows you to use the extended window styles.

Quote: the last one is
how can i get some explains of the OpenGL's variable type,such as GLvoid

I don't know. These typedefs are usually there to ensure platform-independence.