Created an array several times in a loop!

Question

Hi Very strange this code works: for (int i = 0; i { string[] parts = items[i].Split('	'); ...... } It looks the same string array parts is created nItems times but without any error or C# clever enough to created only onece?

Vulpes · Answer

You're correct Dave that you can't declare local variables (i.e. variables within a method or property) which have the same name if the scope of those variables overlap. So this isn't allowed: void MyMethod() { int a = 3; for(int i = 0; i { int a = i + 3; Console.WriteLine(a); } } because the scope of the 'outer' a includes the scope of the 'inner' a. However you can do this because the scope of the 'i's and the 'a's doesn't overlap - they only exist within their respective 'for' statements: void MyMethod() { for(int i = 0; i { int a = i + 3; Console.WriteLine(a); } for(int i = 0; i { int a = i + 6; Console.WriteLine(a); } } The reason the first situation isn't allowed is because if it was then there would be no way to access the 'outer' a from within the for loop. However this rule doesn't prevent you declaring a local variable with the same name as a field because you can always access the field by prefixing it with 'this': class MyClass { private int a = 2; // field declaration void MyMethod() { for(int i = 0; i { int a = i + this.a + 3; Console.WriteLine(a); } } Whilst on the face of it this: int a; for (int i = 0; i { a = i + 3; Console.WriteLine(a); } seems more efficient than this because you're only declaring the local variable a once: for (int i = 0; i { int a = i + 3; Console.WriteLine(a); } in practice there's no appreciable difference because the 'inner' a always uses the same memory location on the stack.

Dave · Answer

Thanks a lot!

Dave · Answer

Now I think string[] parts only create onece although string[] parts = items[i].Split('	') looks being excuted more than onece in a loop? Am I right?

Dave · Answer

Thank you. I think we cannot declare the same array/variable more than once within a procedure like Main? Is this works in a Loop? Or in any other procedure?

Vulpes · Answer

A new string array object is created by items[i].Split('	') on each iteration of the loop and assigned to the local variable 'parts'. So on the final iteration 'parts' will contain the result of items[nItems-1].Split('	'). As each re-assignment to the local variable takes place the previous array object will no longer be referenced and will therefore become eligible for garbage collection.