“ADA.FLOAT_IO”不是预定义的库单元

为什么会出现此错误?

“ADA.FLOAT_IO”不是预定义的库单元

我以前从未在ADA中写过任何东西,只是我不知道自己在做什么。我使用GNAT进行编译。

with Ada.Text_IO; use Ada.Text_IO;
with Ada.Float_IO; use Ada.Float_IO;
with Ada.Numerics.Elementary_Functions;
use Ada.Numerics.Elementary_Functions;

procedure MAIN is
   A,B,C:Float;
   W : Float;
   Re, Im:Float;
begin
   Put("Give A");Get(A);
   Put("Give B");Get(B);
   Put("Give C");Get(C);New_Line;
   if A=0.0 then
      Put_Line("It is not second degree polynomial");
   else
      W:=B*B - 4.0*A*C;
      Re:=B/(2.0*A); Im:=Sqrt(Abs(W))/(2.0*A);
      Put("dif = "); Put(W);New_Line;
      if W<0.0 then
         Put_Line("Complex ");
         Put("x1 = ");Put(-Re);Put(" -j ");Put(Im);Put(" ");
         Put("x2 = ");Put(-Re);Put(" +j ");Put(Im);New_Line;
      else
         Put_Line("Real");
         Put("x1 = ");Put(-Re-Im);Put(" ");
         Put("x2 = ");Put(-Re+Im);
      end if;
   end if;
end MAIN;