COCOS-2d-x: Idea to implement Level progress in games

I have developed a android game with 18 levels. I have menu at starting screen which has 18 buttons for 18 levels.

For example If user dont finish level 1 level 2 button should not be enabled ,and so on.as user finish some levels in game the next level should be enabled. I want to create levels as cpp file and not as a "plist" files