Why cmake .. -GXcode does not generate makefile

I am beginner on cmake. I wrote a CMakeLists.txt file to compile a simple "hello word" example.

cmake_minimum_required(VERSION 2.6)

#Declaration du projet

project(MYfirstcamke)

#set(EXECUTABLE_OUTPUT_PATH bin/${CMAKE_BUILD_TYPE})

#declaration de l'executable

add_executable(

my_executable

main.cpp

)

When I type cmake, It generates a makefile but when I use cmake .. -GXcode. I did get a makefile? What is the problem?