C Sharp code for encription and decription of password or text

C# code of encription and decription

following are two functions. one for encryption and second for decryption. textbox3 is text box to input data and textbox4 is textbox shows encrypted data.

 private void encrypt()  
 {  
 int i = 0; string result = "";  
 string old = textBox3.Text;  
 do  
 {  
 result = result + Convert.ToChar(Convert.ToInt32(old) + (i + 2));  
 i = i + 1;  
 } while (i < old.Length);  
 textBox4.Text = result;  
 textBox3.Text ="";  
 }  
 private void decrypt()  
 {  
 int i = 0; string result = "";  
 string old = textBox4.Text;  
 do  
 {  
 result = result + Convert.ToChar(Convert.ToInt32(old) - (i + 2));  
 i = i + 1;  
 } while (i < old.Length);  
 textBox3.Text = result;  
 textBox4,Text="";  
 }