help!!!- Visual C++ and opengl


i have a damn problem and i cannot solve it, i wanted to check some sample codes for opengl, there are lots of tutorials and sample codes, but i only can execute one of them, and for the others, there is an error occurs;
----error LNK2019: unresolved external symbol _WinMain@16 referenced in function ___tmainCRTStartup
—fatal error LNK1120: 1 unresolved externals

and i cannot find the reason, can anybody please tell me why it happens?

link ur prokject to sdlmain.lib and sdl.lib