用integer存放数据只能计算12以内的阶乘,请问要计算13以上(比如说25)的阶乘应该如何设计呢? ( 积分: 200 )

unit Unit1;



interface



uses

Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,

Dialogs, Borland.Vcl.StdCtrls, System.ComponentModel;



type

TForm1 = class(TForm)

Label1: TLabel;

Label2: TLabel;

Edit1: TEdit;

Edit2: TEdit;

Button1: TButton;

Button2: TButton;

procedure Button2Click(Sender: TObject);

procedure Button1Click(Sender: TObject);

private

{ Private declarations }

public

{ Public declarations }

end;



var

Form1: TForm1;



implementation



{$R *.nfm}



function factorial(n:integer):integer;

begin

result:=1;

while n>1 do

begin

result:=result*n;

n:=n-1;

end;

end;



procedure TForm1.Button2Click(Sender: TObject);

begin

close;

end;



procedure TForm1.Button1Click(Sender: TObject);

var

num:integer;

begin

num:=strtoint(edit1.Text);

if num>12 then

showmessage('输入的数值太大！')

else

edit2.Text:=inttostr(factorial(num));

end;



end.

unit Unit1;



interface



uses

Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,

Dialogs, Borland.Vcl.StdCtrls, System.ComponentModel;



type

TForm1 = class(TForm)

Label1: TLabel;

Label2: TLabel;

Edit1: TEdit;

Edit2: TEdit;

Button1: TButton;

Button2: TButton;

procedure Button2Click(Sender: TObject);

procedure Button1Click(Sender: TObject);

private

{ Private declarations }

public

{ Public declarations }

end;



var

Form1: TForm1;



implementation



{$R *.nfm}



function factorial(n:integer):integer;

begin

result:=1;

while n>1 do

begin

result:=result*n;

n:=n-1;

end;

end;



procedure TForm1.Button2Click(Sender: TObject);

begin

close;

end;



procedure TForm1.Button1Click(Sender: TObject);

var

num:integer;

begin

num:=strtoint(edit1.Text);

if num>12 then

showmessage('输入的数值太大！')

else

edit2.Text:=inttostr(factorial(num));

end;



end.

用int64放不下吗？

int64

用int64只能计算到20的阶乘，20以上（比如说35）的就不行了。

Int64 数值范围-2^63..2^631 数据位数signed 64-bit

自己开辟空间，自己处理进位，注意WORD * WORD 比INTEGER * INTEGER快的多
10000的阶乘 长度好象20K以上，以前我做过

对jshyhzj说：
看不懂，我是个新手，可以讲具体点吗？

可以用字符串啊。

对yyqiheye说：
字符串可以进行加减乘除计算的吗？

这有个别人的无限位数乘法的资料，你参看一下吧
//无限位数乘法
uses StrUtils, Math;

function formatnum(mNumber: string):string;
var
m:integer;
TemStr:string;
begin
Result:='';
for m:=1 to Length(mNumber) do
begin
if mNumber[m]='.' then
Result:=Result+'.'
else
Result:=Result+IntToStr(StrToIntDef(mNumber[m], 0));
end;
while Pos('0', Result) = 1 do Delete(Result, 1, 1); //排除整数前无效的0
if Pos('.', Result )<= 0 then Result := Result + '.'; //没有有小数点补小数点
TemStr:=StrRight(Result,'.');
while Copy(TemStr, Length(TemStr), 1) = '0' do Delete(TemStr, Length(TemStr), 1); //排除小数后无效的0
Result:=StrLeft(Result,'.')+'.'+TemStr;
if Copy(Result, Length(Result), 1) = '.' then Delete(Result, Length(Result), 1); //排除无效小数点
if Result[1]='.' then Result:='0'+Result;
if (Result = '') then Result := '0';
end;

function StrLeft(const mStr: string; mDelimiter: string): string;
begin
Result := Copy(mStr, 1, Pos(mDelimiter, mStr) - 1);
end; { StrLeft }

function StrRight(const mStr: string; mDelimiter: string): string;
begin
if Pos(mDelimiter, mStr) <= 0 then
Result := ''
else Result := Copy(mStr, Pos(mDelimiter, mStr) + Length(mDelimiter), MaxInt);
end; { StrRight }

function InfiniteAdd(mNumberA, mNumberB: string): string; { 无限位数加法 }
var
I: Integer;
T: Integer;
begin
Result := '';
if Pos('.', mNumberA) <= 0 then mNumberA := mNumberA + '.'; //没有有小数点补小数点
if Pos('.', mNumberB) <= 0 then mNumberB := mNumberB + '.'; //没有有小数点补小数点
I := Max(Length(StrLeft(mNumberA, '.')), Length(StrLeft(mNumberB, '.'))); //整数部分最大长度
mNumberA := DupeString('0', I - Length(StrLeft(mNumberA, '.'))) + mNumberA; //整数前补0
mNumberB := DupeString('0', I - Length(StrLeft(mNumberB, '.'))) + mNumberB; //整数前补0
T := Max(Length(StrRight(mNumberA, '.')), Length(StrRight(mNumberB, '.'))); //小数部分最大长度
mNumberA := mNumberA + DupeString('0', T - Length(StrRight(mNumberA, '.'))); //小数后补0
mNumberB := mNumberB + DupeString('0', T - Length(StrRight(mNumberB, '.'))); //小数后补0
I := I + T + 1; //计算总长度//小数长度和整数长度加上小数点长度
T := 0; //进位数初始化
for I := I downto 1 do //从后向前扫描
if [mNumberA, mNumberB] <> ['.'] then begin //不是小数点时
T := StrToIntDef(mNumberA, 0) + T; //累加当前数位
T := StrToIntDef(mNumberB, 0) + T; //累加当前数位
Result := IntToStr(T mod 10) + Result; //计算当前数位上的数字
T := T div 10; //计算进位数
end else Result := '.' + Result; //加上小数点
if T <> 0 then Result := IntToStr(T mod 10) + Result; //处理进位数
while Pos('0', Result) = 1 do Delete(Result, 1, 1); //排除整数前无效的0
while Copy(Result, Length(Result), 1) = '0' do
Delete(Result, Length(Result), 1); //排除小数后无效的0
if Copy(Result, Length(Result), 1) = '.' then
Delete(Result, Length(Result), 1); //排除无效小数点
if Copy(Result, 1, 1) = '.' then Result := '0' + Result; //处理无0小数情况
if (Result = '') then Result := '0'; //处理空字符情况
end; { InfiniteAdd }

function InfiniteMult(mNumberA, mNumberB: string): string; { 无限位数乘法 }

function fMult(mNumber: string; mByte: Byte): string; { 无限位数乘法子函数 }
var
I: Integer;
T: Integer;
begin
Result := '';
T := 0;
for I := Length(mNumber) downto 1 do begin //从后向前扫描
T := StrToIntDef(mNumber, 0) * mByte + T; //累加当前数位
Result := IntToStr(T mod 10) + Result; //计算当前数位上的数字
T := T div 10; //计算进位数
end;
if T <> 0 then Result := IntToStr(T mod 10) + Result; //处理进位数
end; { fMult }

var
I: Integer;
vDecimal: Integer; //小数位数
T: string;
begin
Result := '';
///////Begin 处理小数
if Pos('.', mNumberA) <= 0 then mNumberA := mNumberA + '.'; //没有有小数点补小数点
if Pos('.', mNumberB) <= 0 then mNumberB := mNumberB + '.'; //没有有小数点补小数点
vDecimal := Length(StrRight(mNumberA, '.')) + Length(StrRight(mNumberB, '.')); //计算小数位数
mNumberA := StrLeft(mNumberA, '.') + StrRight(mNumberA, '.'); //删除小数点
mNumberB := StrLeft(mNumberB, '.') + StrRight(mNumberB, '.'); //删除小数点
///////End 处理小数
T := '';
for I := Length(mNumberB) downto 1 do begin
Result := InfiniteAdd(Result, fMult(mNumberA, StrToIntDef(mNumberB, 0)) + T);
T := T + '0';
end;
Insert('.', Result, Length(Result) - vDecimal + 1);
while Pos('0', Result) = 1 do Delete(Result, 1, 1); //排除整数前无效的0
while Copy(Result, Length(Result), 1) = '0' do
Delete(Result, Length(Result), 1); //排除小数后无效的0
if Copy(Result, Length(Result), 1) = '.' then
Delete(Result, Length(Result), 1); //排除无效小数点
if Copy(Result, 1, 1) = '.' then Result := '0' + Result; //处理无0小数情况
if (Result = '') then Result := '0'; //处理空字符情况
end; { InfiniteMult }

procedure TForm1.Button1Click(Sender: TObject);
begin
Edit3.Text := InfiniteMult(Edit1.Text, Edit2.Text);
end;

为什么不能直接把integer改为single呢？

谢谢！

多人接受答案了。