I have the following code that I am currently using to call functions from a C# Dll, which works perfectly in Visual C++.
#pragma comment(lib, "mscoree.lib")
ICLRRuntimeHost *pHost = NULL;
HRESULT hr = CorBindToRuntimeEx(L"v4.0.30319", L"wks", 0, CLSID_CLRRuntimeHost, IID_ICLRRuntimeHost, (PVOID*)&pHost);
// target method MUST be static int method(string arg)
DWORD dwRet = 0;
hr = pHost->ExecuteInDefaultAppDomain(L"c:\\temp\\test.dll", L"Test.Hello", L"SayHello", L"Person!", &dwRet);
hr = pHost->Stop();
Code::Blocks is a great IDE for C++ programming, but you are clearly doing Windows programming here. Though it is the same programming language, compilers are not compatible among them.
Either if you have downloaded the CodeBlocks version with the gcc compiler, or the single CodeBlocks IDE, you need to configure CodeBlocks in order to use the MS C++ compiler. In order to do that, go to Settings >> Compiler and debugger >> Toolchain executables.
Also, in the same option, look for Search directories and place there the path to the MS C++ compiler headers.
Once that is done, you will be able to compile your program.