C#, Declaring a variable inside for..loop, will it decrease performance? [duplicate]

Question

For example:

            for (i = 0; i < 100; i++)
            {
               string myvar = "";
                // Some logic
            }

Do it make performace or memory leak?

Why i do this, because i don't want "myvar" accessible outside the for..loop.

It is any performance monitor, i can compare the execute time between two snippet or whole program ?

thanks you.

Answer 1

No, variables are purely for the programmer's convenience. It doesn't matter where you declare them. See my answer to this duplicate question for more details.

Answer 2

Perhaps you could check out an old test that I once did regarding another conversation. Variable declaration. Optimized way

The results turned out that it was faster to redefine but not as easy on memory.

My simple test. I initialised an object 100,000,000 times and it is was apparently faster to create a new one instead of re-using an old one :O

    string output = "";
    {
        DateTime startTime1 = DateTime.Now;
        myclass cls = new myclass();
        for (int i = 0; i < 100000000; i++)
        {
            cls = new myclass();
            cls.var1 = 1;
        }
        TimeSpan span1 = DateTime.Now - startTime1;
        output += span1.ToString();
    }

    {
        DateTime startTime2 = DateTime.Now;
        for (int i = 0; i < 100000000; i++)
        {
            myclass cls = new myclass();
            cls.var1 = 1;
        }
        TimeSpan span2 = DateTime.Now - startTime2;
        output += Environment.NewLine + span2.ToString() ;
    }
    //Span1 took 00:00:02.0391166
    //Span2 took 00:00:01.9331106

public class myclass
{
    public int var1 = 0;
    public myclass()
    {
    }
}