program ExtractDigits;
{$mode objfpc}{$H+}{$H-}
{
This program demonstrates how to scan a string and collect
only the digit characters ('0'..'9') into a new string.
It uses:
- A dedicated function for clarity
- Built‑in character classification (using standard operators)
- A simple and efficient linear scan
}
{
ExtractDigits
-------------
Walks through the input string and appends every digit
to a result string.
Parameters:
S : the input string to examine
Returns:
A string containing only the digit characters found in S.
}
function ExtractDigits(const S: string): string;
var
i: Integer;
resultDigits: string;
begin
resultDigits := '';
{ Iterate through each character in the string }
for i := 1 to Length(S) do
begin
{ Check whether the character is a digit using Pascal's built‑in range test }
if (S[i] in ['0'..'9']) then
resultDigits := resultDigits + S[i];
end;
{ Return the collected digits }
Result := resultDigits;
end;
var
str: string;
digits: string;
begin
{ Example input string }
str := '5 ruby8go 9001 c c++ 17python';
{ Extract all digits }
digits := ExtractDigits(str);
{ Display results }
WriteLn('Original: ', str);
WriteLn('Digits: ', digits);
end.
{
run:
Original: 5 ruby8go 9001 c c++ 17python
Digits: 58900117
}
