error LNK2019

hello,
my english is not very well but i try to explain my problem.

i try to run my first opencl project with this tutorial
http://developer.amd.com/gpu/ATIStreamSDK/pages/TutorialOpenCL.aspx

if i use this method cl::Context context(CL_DEVICE_TYPE_CPU, 0, NULL, NULL, &err);

i get this error. (Link unresolved external symbol)
error LNK2019 _clCreateContextFromType in function public: __thiscall cl::Context::Context(unsigned __int64,int ,void (__cdecl)(char const *,void const *,unsigned int,void *),void *,int *)

error LNK2019 _clReleaseContext" in function public: static int __cdecl cl::detail::ReferenceHandler<struct _cl_context *>::release(struct _cl_context *)

need help
best regards