s:=floattostr(a5) ;这一行出问题了，想不通，咋整？

Question

var a1,a2,a3,a4,a5 : double ;s:string;begina1:= strtofloat(trim(edit1.Text ));a2:=strtofloat (trim(edit2.Text ));a3:=strtofloat (trim(edit3.Text ));a4:=strtofloat (trim(edit4.Text ));tryif RadioButton1.Checked=true thena5:=((a1 * 2) / a3*a4+a2)*1.1s:=floattostr(a5) ;showmessage(s);

Answer 1

就s:=floattostr(a5);这一行代码本身是没问题的
function FloatToStr(Value: Extended): string; overload;
function FloatToStr(Value: Extended; const FormatSettings: TFormatSettings): string; overload;

我简单测试了你的程序，
procedure TForm1.btn1Click(Sender: TObject);
var a1,a2,a3,a4,a5 : double ;
s:string;
begin

a1:=1.0;
a2:=3.0;
a3:=2.0;
a4:=4.0;

a5:=((a1 * 2) / a3*a4+a2)*1.1;

s:=floattostr(a5) ;
showmessage(s);
end;
运行结果显示了7.7

看看是不是其他地方造成的错误

Answer 2

floattostr
没有这个函数
浮点转字符
format('%e',[a5])

Answer 3

caption := FormatFloat('###,##.###', 2340283.23423432);
caption := Format('%.3f',[345435.345845]);