CMakeLists.txt add_definitions
cmake_minimum_required(VERSION 3.2)
option(DEBUG "Option description" OFF)
if(DEBUG)
add_definitions(-DDEBUG)
endif(DEBUG)
add_executable(cond conditional.cpp)
without debug
$ cmake ..
$ make
$ ./cond
WITH debug
$ cmake -DDEBUG=ON ..
$ make
$ ./cond
a[0] = 2
a[1] = 3
a[2] = 4
a[3] = 5