Base Converter Program (2/8/10/16)

Program covertion;
Uses Wincrt;
Var
  b1,b2: Integer;
  ch1: String;
    x:char;

Function verif (ch:String): Boolean;
Var
  i: Integer;
    test:Boolean;
Begin
  i := 0;
  Repeat
    i := i+1;
    test := ch[i] In['A'..'F','0'..'9'];
  Until (i=Length(ch)) Or (test=False);
    verif:=test;
End;
Function convb1 (ch:String;x1:integer): Integer;
Var
s,i,p,e,x:Integer;
Begin
  p := 1;
  s := 0;
  For i:=Length(ch) downto 1 Do
    Begin
            if (ch[i] in ['A'..'F']) Then
                begin
                s:=s+p*ord(ch[i])-55;
                p:=p*x1 ;
                end
                else
                begin
                        val (ch[i],x,e);
                            s:=s+p*x;
                p:=p*x1 ;
                end;
        End;
        convb1:=s;
End;
Procedure saisie (Var ch1:String;Var b1,b2:Integer);
Begin
  Repeat
        ClrScr;
        Write ('Saisir la premiere base: ');
    Readln (b1);
    Write ('Saisir la deuxieme base: ');
    Readln (b2);
        if (b2=b1) Then
            begin
                writeln ('Vous avez saisi la meme base deux fois !');
                delay (1500);
            end;
        if (not (b1 in [2,8,10,16])) or (not(b2 in [2,8,10,16])) Then
            begin
                writeln ('Verifiez les bases saisies!');
                delay (1500);
            end;
  Until (2<=b2) And (b2<=16) And (2<=b1) And (b1<=16) and (b1 in [2,8,10,16]) and (b2 in [2,8,10,16]) and (b2<>b1);
  Repeat
    Write ('Saisir la chaine: ');
    Readln (ch1);
  Until verif (ch1);
End;
Function convb2 (b2,n:integer): String;
Var
  i: Integer;
  ch,ch1: String;
Begin
  ch := '';
  Repeat
    If (n Mod b2>9) Then
      Begin
        i := 55+n Mod b2;
        ch := ch+Chr(i);
        n := n Div b2;
      End
    Else
      Begin
        Str (n Mod b2,ch1);
        ch := ch+ch1;
        n := n Div b2;
      End;
  Until (n=0);
  ch1 := '';
  For i:=Length(ch) Downto 1 Do
    ch1 := ch1+ch[i];
  convb2 := ch1;
End;
function conv (ch:string;b1,b2:integer):string;
Var
x:integer;
Begin
    x:=convb1 (ch,b1);
    ch:=convb2 (b2,x);
    conv:=ch;
end;
Begin
    Repeat
        ClrScr;
        saisie (ch1,b1,b2);
        Writeln ('(',ch1,')',b1,'=(',conv(ch1,b1,b2),')',b2);
        writeln ('Voulez vous continuer? O/N');
        readln (x);
    until (x='N') or (x='n');
End.