How to write something but caret maintain its position?

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C#

I have this event which perform some computations inside it (the "for" ones)
The caret inside textBox1(for each letter I write), is redirected to the beginning of text after those computations, and thats why I inserted the last line in code provided, to rectify that bug: textBox1.SelectionStart = textBox1.Text.Length;
[I know that "SelectionStart" is in fact the caret position, but because of the computation, it start as I explained]
Now my problem is: When I want to insert a NEW text in the interior of the text, for each letter I write, the caret goes to the end of the text(because of the last line mentioned). How to write something but caret maintain its position?
Thanks.
Here is the code:

//Here are 4 arrays with chars.
     private void textBox1_TextChanged(object sender, EventArgs e) 
     {
            for (int i = 0; i < literaRom.Length; i++)
            {
                if (textBox1.Text.Contains(literaRom[i]))//lower
                    textBox1.Text = textBox1.Text.Replace(literaRom[i], literaRus[i]);
                if (textBox1.Text.Contains(literaRom[i].ToUpper()))//upper
                    textBox1.Text = textBox1.Text.Replace(literaRom[i].ToUpper(), literaRus[i].ToUpper());
            }

            for (int i = 0; i < literaKeyComp.Length; i++)
            {
                if (textBox1.Text.Contains(literaKeyComp[i]))//lower
                    textBox1.Text = textBox1.Text.Replace(literaKeyComp[i], literaRusComp[i]);
                if (textBox1.Text.Contains(literaKeyComp[i].ToUpper()))//upper
                    textBox1.Text = textBox1.Text.Replace(literaKeyComp[i].ToUpper(), literaRusComp[i].ToUpper());
            }


             textBox1.SelectionStart = textBox1.Text.Length;//redirected cursor (put carret at end of text)
     }