String, pchar, and character array (Delphi)

There are three variables:
VaR
S: string;
P: pchar;
A: array [1 .. 20] of char;
The conversion between the three is as follows:
1. string to pchar
P: = pchar (s );
2. pchar to string
S: = P;
3. pchar to character array
Strcopy (@ A, P );
4. character array to pchar
Pchar (@ );
5. The conversion between the string and character array is only through pchar. For example:
Procedure tform1.btn1click (Sender: tobject );
VaR
STR: array [1 .. 10] of char;
Begin
Strcopy (@ STR, pchar (mmo1.text ));
Mmo2.text: = pchar (@ Str );
End;