Subject: From string to real

55. *****
 Q: How can I test and convert a numerical string into a real?

 A1: An easy task in Turbo Pascal but in standard Pascal this
frequent task is much trickier. Here are both the Turbo Pascal and
Standard Pascal versions for general edification :-).
  (* Convert and test a numerical string with Turbo Pascal *)
  function DIGVALFN (mj : string; var ok : boolean) : real;
  var k : integer;
      x : real;
  begin
    Val (mj, x, k);
    ok := k = 0;
    if ok then digvalfn := x else digvalfn := 0;
  end;  (* digvalfn *)
  {}
  (* Convert and test a numerical string with standard Pascal routines only *)
  procedure DIGVAL (mj : string; var number : real; var ok : boolean);
  label 1;
  var il, lenl, pl, kl1, kl2 : integer;
      nrol                   : boolean;
      numberdl               : real;
  begin
    ok := true; lenl := Length (mj); nrol := false; pl := 0; number := 0.0;
    if lenl = 0 then ok := false;
    for il:=2 to lenl do if (mj[il]='-') or (mj[il]='+') then ok := false;
    for il:=1 to lenl do
      case mj[il] of
        '0'..'9','+','-','.' : ; else ok := false;
      end;
    for il:=1 to lenl do
      case mj[il] of '0'..'9' : begin nrol := true; goto 1; end; end;
    1: if nrol = false then ok := false;
    for il:=1 to lenl do if mj[il] = '.' then pl := pl + 1;
    if pl > 1 then ok := false;
    kl1:=1; kl2:=lenl+1; if (mj[1]='-') or (mj[1]='+') then kl1 := 2;
    for il:=1 to lenl do if mj[il] = '.' then kl2 := il;
    if kl2-kl1 > 38 then ok := false;
    if ok then
      begin
        number:=0; numberdl:=0;
        for il:=kl1 to kl2-1 do number := (ord(mj[il])-48)+10*number;
        if kl2 < lenl+1 then
          for il:=lenl downto kl2+1 do
            numberdl := (ord(mj[il])-48)/10+numberdl/10;
        number := number + numberdl;
        if mj[1]='-' then number := -number;
      end; {if ok}
  end;  (* digval *)
  {}
  procedure TEST;
  var s : string; r : real; ok : boolean;
  begin
    s := '123.41';
    r := DIGVALFN (s, ok);
    if ok then writeln (r) else writeln ('Error in ', s);
    DIGVAL (s, r, ok);
    if ok then writeln (r) else writeln ('Error in ', s);
  end;

A2: The conversion can be in the other directorion as well. Here is
how to convert an integer into a string with standard Pascal
routines only.
  function CHRIVLFN (number : integer) : string;
  var il, pl, al : integer;
  cl, mj : string;
  isNeg : boolean;
  begin
    if number < 0 then begin
      isNeg := true; number := -number; end
      else isNeg := false;
    pl := 0; mj := ''; cl := '';
    repeat
      pl := pl + 1;
      al := number mod 10;
      cl := cl + chr(al+48);
      number := number div 10;
    until number = 0;
    if isNeg then begin pl := pl + 1; cl[pl] := '-'; end;
    for il := 1 to pl do mj := mj + cl[pl+1-il];
    chrivlfn := mj;
  end;  (* chrivlfn *)
  {}
  procedure TEST;
  var s : string; j : integer;
  begin
    j := 12341;
    s := CHRIVLFN (j);
    writeln (s);
  end;
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