variable scope in statement blocks

Question

for (int i = 0; i < 10; i++)
{
    Foo();
}
int i = 10; // error, \'i\' already exists

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for (int i = 0; i < 10; i         


        

Answer 1

From the C# spec on local variable declarations:

The scope of a local variable declared in a local-variable-declaration is the block in which the declaration occurs.

Now, of course, you can't use i before it is declared, but the i declaration's scope is the entire block that contains it:

{
    // scope starts here
    for (int i = 0; i < 10; i++)
    {
        Foo();
    }
    int i = 10;
}

The for i variable is in a child scope, hence the collision of variable names.

If we rearrange the position of the declaration, the collision becomes clearer:

{
    int i = 10;

    // collision with i
    for (int i = 0; i < 10; i++)
    {
        Foo();
    }
}