编写 C# 代码以返回每个字母大小写颠倒的字符串

Question

C# 中有合适的函数可以做到这一点吗？

 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();
}