{program power;           User shell to calculate a^k (mod m)}
{$N+,E+}
uses CRT, nothy;
{$I GetInput.i }

var
a,                        {the base}
k,                        {the exponent}
m,                        {the modulus}
b                         {the resulting residue class}
         : comp;

x        : extended;
i,                        {an index}
code                      {Error code in translating a string
                           to a real number}
         : integer;

begin              {main body}
  if ParamCount = 3
  then
    begin
      Val(ParamStr(1), x, code);
      if (frac(x) = 0) and (code = 0) and (Abs(x) < MaxAllow)
      then a := x
      else Halt;
      Val(ParamStr(2), x, code);
      if (frac(x) = 0) and (code = 0) and (x >= 0) and (x < MaxAllow)
      then k := x
      else Halt;
      Val(ParamStr(3), x, code);
      if (frac(x) = 0) and (code = 0) and (x > 0) and (x < MaxAllow)
      then m := x
      else Halt
    end
  else
    begin
      WriteLn('Will find a^k (mod m) where');
      a := GetInput(WhereX, WhereY, '     a = ',
          '  (³a³ ó 999999999999999999)', -MaxAllow-1, MaxAllow-1);
      k := GetInput(WhereX, WhereY, '     k = ',
          '(0 ó k ó 999999999999999999)', 0, MaxAllow-1);
      m := GetInput(WhereX, WhereY, '     m = ',
          '(1 ó m ó 999999999999999999)', 1, MaxAllow-1);
    end;
b :=  power(a, k, m);
if ParamCount <> 3
then for i := 1 to 4 do
    begin
      GoToXY(1, WhereY - 1);
      ClrEoL
    end;
  WriteLn;
  Write(a:1:0);
  GoToXY(WhereX, WhereY - 1);
  Write(k:1:0);
  GoToXY(WhereX, WhereY + 1);
  WriteLn(' ð ', b:1:0, ' (mod ', m:1:0, ')');
end.