For loop variable declaration for the condition in .NET Source code

Question

I've been digging through ExpressionVisitor in .NET and I found this for loop,

for (int i = 0, n = nodes.Count; i < n; i++) 
{
    Expression node = Visit(nodes[i]);
    if (newNodes != null) 
    {
        newNodes[i] = node;
    } 
    else if (!object.ReferenceEquals(node, nodes[i])) 
    {
        newNodes = new Expression[n];
        for (int j = 0; j < i; j++) 
        {
            newNodes[j] = nodes[j];
        }
        newNodes[i] = node;
    }
}

Now is there any particular reason why is that: i = 0, n = nodes.Count; i < n?

Is there any performance gain from this that is not in i = 0; i < nodes.Count?

Answer 1

It is best practice to use a variable when you use the same statement more than once.

Here, nodes.Count is used in two places as below and hence, variable was used instead of executing the same statement twice.

for (int i = 0, n = nodes.Count; i < n; i++) {

And,

newNodes = new Expression[n];

Note: As discussed in the comments, performance difference is completely negligible though.

Answer 2

I don't think it has any much performance effects in this case. But as they are using this n is this line as well,

newNodes = new Expression[n];

So,

• Program has to get node.Count only once.
• n need not to be assigned again.
• Looks much cleaner.

That's all there is to it.