C# 7.0 adds a new feature called local functions.
Local functions allow us to define function within a function. It can be used to write helper methods that we need to use inside that function’s scope.
Here in the below sample code we have defined one main function (MainFunction) that has one local function(MultiplyBy10LocalFunction) defined inside it. And that local function has one more local function(Add10LocalFunction) defined inside it.
Hope it helps..