I don’t understand how xa can be converted to 10 in Borland Pascal. I just use
Val('xa', value, return);
and value becomes 10, and return becomes 0 (meaning successful conversion). I’m just a newbie, can anyone explain this? I know this won’t like the ASCII cause that is just a character.
And I’m using Free Pascal ☺
I tested it in Free Pascal using xa, 0xa and $xa. So, I think Val understands the special characters like $ or 0 without me needing to call specialized functions like Hex2Dec. Is that right?
Since early Delphi's, the core integer conversion routines don't do just number sequences, but also some specials like Pascal "$924" for hex or C style 0x02).
FreePascal adopted it when it later started adding Delphi compatibility (roughly 1997-2003). Beside this difference, another different is that the last parameter (RETURN in your example) changed from WORD (in Turbo Pascal) to integer/longint in Delphi.
IOW, the routine accepts the x and thinks you mean to convert a C style hex number, and then interprets the "a" according to Stuart's table.
It also interprets % as binary, and & as octal.
Try
val('$10',value,return);
writeln(value,' ' ,return); // 16 0
val('&10',value,return);
writeln(value,' ' ,return); // 8 0
val('%10',value,return);
writeln(value,' ' ,return); // 2 0
and compare the results.
Note that this probably won't work for very old Pascal's like Turbo Pascal, and Free Pascals from before the year 2000. The % and & are FPC specific to match the literal notation extensions (analogous to $, but for binary and octal)
var x : Integer
begin
x:=%101010; //42
x:=&101; //65