STRING / PCHAR / CHAR in Delphi

STRING / PCHAR / CHAR in Delphi
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Char
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Char is a data type that holds only one character as value. Ansi Characters are used to store single byte ansi characters. Unicode
characters are used to store 2byte characters that is to cupport foreign languages like chinese, japanese etc.
var
   chr1 : Char;        // Holds a single character, alphabet
   chr2 : WideChar;    // Holds a single character, International alphabet // for Unicode support
   chr3 : AnsiChar;    // Holds a single character, alphabet

NON-PRINTING OR CONTROL CHARACTERS, NOT USED IN THIS CLASS, INCLUDED FOR INTEREST ONLY
 0 Null (nothing)
 7 Bell
 8 Back space
 9 Tab
10 Line feed (new line at present column)
13 Carriage return (return to beginning of line)
26 End of file
27 [Esc] (Escape key)
ASCII CHARACTER CODES
32 [space]   64 @          96 `
33 !         65 A          97 a
34 "         66 B          98 b
35 #        67 C          99 c
36 $        68 D         100 d
37 %       69 E         101 e
38 &        70 F         102 f
39 '         71 G         103 g
40 (        72 H          104 h
41 )        73 I           105 i
42 *        74 J          106 j
43 +       75 K          107 k
44 ,         76 L          108 l
45 -         77 M         109 m
46 .         78 N         110 n
47 /         79 O         111 o
48 0         80 P         112 p
49 1         81 Q         113 q
50 2         82 R         114 r
51 3         83 S         115 s
52 4         84 T         116 t
53 5         85 U         117 u
54 6         86 V         118 v
55 7         87 W        119 w
56 8         88 X         120 x
57 9         89 Y         121 y
58 :         90 Z         122 z
59 ;         91 [          123 {
60 <         92 \         124 |
61 =         93 ]         125 }
62 >         94 ^        126 ~
63 ?         95 _

String
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String is a data type this kind of variables holds sequence of characters as value. In old version String = Ansistring.
But in new versions from Delphi 2010 it is Unicodestring / WideString. String starts with index 1 and 0 index stores
length of the string. SO we can find end of string by its length. Maximum length is depend on available memory. In Delphi string
is reference counted. So delphi will automatically frees a string datatype. Delphi doesn't support automatic type conversions
betwwen Ansi and Wide string types.
var
   Str4 : ShortString; // Holds a string of up to 255 Char's
   Str5 : String;      // Holds strings of Char's of any size desired
   Str6 : AnsiString;  // Holds strings of AnsiChar's any size desired
   Str7 : WideString;  // Holds strings of WideChar's of any size desired   // for Unicode support/ so same as Unicodestring
   str9 : Unicodestring// same as widestring
   str8 : string[20];  // maximum 20 characters      
String system functions
 AnsiLeftStr        Returns leftmost characters of a string
 AnsiMidStr         Returns middle characters of a string
 AnsiRightStr       Returns rightmost characters of a string
 AnsiStartsStr      Does a string start with a substring?
 AnsiContainsStr    Does a string contain another?
 AnsiEndsStr        Does a string end with a substring?
 AnsiIndexStr       Check substring list against a string
 AnsiMatchStr       Check substring list against a string
 AnsiReverseString  Reverses characters in a string
 AnsiReplacStr      Replaces all substring occurences
 DupeString         Repeats a substring n times
 StrScan            Scans a string for a specific character
 StuffString        Replaces part of a string text
 Trim               Removes leading and trailing white space
 TrimLeft           Removes leading white space
 TrimRight          Removes trailing white space
 Converting from numbers to strings
 CurrToStrF        Convert a currency value to a string with formatting
 DateTimeToStr     Converts TDateTime date and time values to a string
 DateTimeToString  Rich formatting of a TDateTime variable into a string
 DateToStr         Converts a TDateTime date value to a string
 FloatToStr        Convert a floating point value to a string
 FloatToStrF       Convert a floating point value to a string with formatting
 Format            Rich formatting of numbers and text into a string
 FormatCurr        Rich formatting of a currency value into a string
 FormatDateTime    Rich formatting of a TDateTime variable into a string
 FormatFloat       Rich formatting of a floating point number into a string
 IntToHex          Convert an Integer into a hexadecimal string
 IntToStr          Convert an integer into a string
 Str               Converts an integer or floating point number to a string
 Converting from strings to numbers
 StringToWideChar  Converts a string into a WideChar 0 terminated buffer
 StrToCurr         Convert a number string into a currency value
 StrToDate         Converts a date string into a TDateTime value
 StrToDateTime     Converts a date+time string into a TDateTime value
 StrToFloat        Convert a number string into a floating point value
 StrToInt          Convert an integer string into an Integer value
 StrToInt64        Convert an integer string into an Int64 value
 StrToInt64Def     Convert a string into an Int64 value with default
 StrToIntDef       Convert a string into an Integer value with default
 StrToTime         Converts a time string into a TDateTime value
 Val               Converts number strings to integer and floating point values

PCHAR
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Pchar is a datatype (pointer of characters) that holds array of characters or single character. It is null terminated string like C.
It starts from 0 index. In Delphi it is mostly used for Windows API function calls. Since the array has no length indicator, Delphi uses
the ASCII 0 (NULL; #0) character to mark the boundary of the string.  It allowed strings of any length, limited only by how much memory
the native pointer type can access.
var
p1: Pchar;
chr1: char;
s1: string;
chr2: char;
.
.
p1:='abcdefgh';
chr1:=p1[0];
s1:=p1;
chr2:=s1[1];
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procedure TForm1.Button1Click (Sender: TObject);
var
  S1: String;
begin
  SetLength (S1, 100);
  GetWindowText (Handle, PChar (S1), Length (S1));
  Button1.Caption := S1;
end;
S1 := String (PChar (S1));