Problem with CMAKE_CXX_COMPILER

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Hi guys, I have a problem with my cmake compiler.

I have Ubuntu 14.04 LTS and ROS-Indigo. I had Cmake version 2.8.13 and gcc version 4.8. I wanted to update cmake and gcc compiler. Now I have cmake version 3.81 and gcc version 6.2.0. After that update i cannot build my packages. I'm getting erorr like that:

The CXX compiler identification is unknown
CMake Error in :
  No CMAKE_CXX_COMPILER could be found.

  Tell CMake where to find the compiler by setting either the environment
  variable "CXX" or the CMake cache entry CMAKE_CXX_COMPILER to the full path
  to the compiler, or to the compiler name if it is in the PATH.

I think i have to change the path of the compiler but i do not know how. Could you help me? Should i remove ROS and install again?