怎么判断一个字符串是数字？

[CoolDesigner]

怎么判断一个字符串是数字？

[CoolDesigner]

如果类似20.5带有小数点的数？怎么办

[cnhgj]

也可以在输入时在keypress里判断

if not (key int ['0'..'9',#48]) then
begin
key:=#0;
beep;
end;

[dichun]

try
var,
strtoint,
strtoint64,
strtofloat,
except
end;
在ONKEYPRESS
if not (key int ['0'..'9',#48，#8]) then
begin
key:=#0;
end;
等

[CoolDesigner]

int 是什么关键字？怎么报错！

[wanjichuansuo]

function isNum(s:string):Boolean;
var
p:pchar;
i,j:integer;
begin
Result:=true;
i:=Strlen(s);
GetMem(p,128);
StrPcopy(p,s);
For j:=0 to i-1 do
begin
if not(p[i] in [0..9]) then
Result:=false;
end;
Freemem(p,128);
end;

[kellerlee]

unit Unit1;

interface

uses
Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
Dialogs, StdCtrls;

type
TForm1 = class(TForm)
Button1: TButton;
Edit1: TEdit;
procedure Button1Click(Sender: TObject);
private
{ Private declarations }
public
function nu(mstr:string):boolean;
{ Public declarations }
end;

var
Form1: TForm1;

implementation

{$R *.dfm}
function TForm1.nu(mStr: string): Boolean; { 返回字符串是否是正确的数字表达 }

var

I: Real;

E: Integer;

begin

Val(mStr, I, E);

Result := E = 0;

E := Trunc(I);

end;

procedure TForm1.Button1Click(Sender: TObject);


begin

if nu(edit1.Text )=true then
application.MessageBox('全是数字','',mb_ok)
else
application.MessageBox('全是数字','',mb_ok)
end;


end.

[风行者009]

if not (key int ['0'..'9',#48，#8]) then
begin
key:=#0;
end;

[ilovedbb]

val

[nuaabestbo]

val(str,i,j);
if j=0 then showmessage('str是数字')；

[suuare]

for i:=1 to length(Str) do
begin
if not (Str[i] in [0..9] then)
ShowMessage('不是!');

end;

[yhj78]

try
strtofloat(变量);/strtoint(变量);
except
showmessage('错误');

end;
这样最简单。

[lion_lh]

try
strtofloat('fdf')
except
showmessage('错');
end;

[shao528]

val函数可以，具体看help

[Comer]

try
strtofloat('123')
except
end;

[darkhorsedba]

shao528(远洋)说的对，val比try..except结构要好！！

[xiaoyuer0851]

呵呵，同意
方法有很多种，关键是 看大家愿意使用哪种

[darkhorsedba]

i,j:integer;
val(str,i,j);
if j=0 then
showmessage('str是数字')；

[foilsman]

uses SysUtils;


var
s : String;
I : Integer;
begin
s := '2254334';
TryStrToInt(s, i);
if Length(IntToStr(I)) < Length(s) then
ShowMessage('不是一个整数');
end;

[gototop99]

var
I, Code: Integer;
begin
Val(Edit1.Text, I, Code);
if Code <> 0 then
MessageDlg('Error at position: ' + IntToStr(Code), mtWarning, [mbOk], 0)
else
Canvas.TextOut(10, 10, 'Value = ' + IntToStr(I));
end;

[hiflower]

v:variant;
s:string;
f:extended;

v:=s;
try
f:=v;
except
//不是数字
end;