Created an array several times in a loop!

Dave

Hi,
Very strange, this code works:
for (int i = 0; i < nItems; i++)
{
string[] parts = items[i].Split('\t');
......
}
It looks the same string array "parts" is created nItems times but without any error, or C# clever enough to created only onece?

5 Replies

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Vulpes12y ago
Accepted 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 < 10; 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 < 10; i++)
{
int a = i + 3;
Console.WriteLine(a);
}

for(int i = 0; i < 10; 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 < 10; i++)
{
int a = i + this.a + 3;
Console.WriteLine(a);
}
}

Whilst, on the face of it, this:

int a;
for (int i = 0; i < 10; 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 < 10; 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.
Dave12y ago
Thanks a lot!
Dave12y ago
Now, I think string[] parts only create onece although
string[] parts = items[i].Split('\t')
looks being excuted more than onece in a loop? Am I right?
Dave12y ago
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?
Vulpes12y ago
A new string array object is created by items[i].Split('\t') 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('\t').

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.