Unresolved external symbol

I get the unresolved external symbol error message when trying to build my program.
 
 unresolved external symbol _Process32Next@8
 unresolved external symbol _Process32First@8
 unresolved external symbol _CreateToolhelp32Snapshot@8

From the code section:-
void Snap()
      {
      HWND hSnap;

      hSnap = CreateToolhelp32Snapshot(TH32CS_SNAPPROCESS, 0);

    if (hSnap ==(HANDLE) -1)
      {
            MessageBox();
      }
      else
      {
            PROCESSENTRY32 procEntry;
            procEntry.dwSize = sizeof(PROCESSENTRY32);

            if (!Process32First(hSnap, &procEntry))
            {
                  //this can't possibly happen
                  MessageBox();
                  assert(FALSE);
            }
            else
            {
                  BOOL bResult;
                        do
                  {
                  
                  bResult = Process32Next(hSnap, &procEntry);
                  } while (bResult);
            }
            CloseHandle(hSnap);
      }
      }