すべての文字の大文字と小文字を逆にして文字列を返すC＃コードを書く

Question

C＃で適切な機能を持っていますか？

private void button1_Click(object sender, EventArgs e) 
{ 
    string s1 = textBox1.Text; 
} 

Answer 1

string s1 = new string(
    textBox1.Text.Select(ch => char.IsLetter(ch) ? (char.IsUpper(ch) ? 
         char.ToLower(ch) : char.ToUpper(ch)) : ch).ToArray()); 

Answer 2

public string RevString() 
{ 
    var s = "TestThisString"; 
    StringBuilder sb = new StringBuilder(); 
    var arr = s.ToCharArray(); 

    foreach (var c in arr) 
    { 
     if (c.ToString() == c.ToString().ToLower()) 
     { sb.Append(c.ToString().ToUpper());} 
     else 
     { sb.Append(c.ToString().ToLower()); } 
    } 
    return sb.ToString(); 
}