2021-11-28 Delphi新语法 For ..In 循环

https://www.cnblogs.com/del/archive/2008/11/12/1332011.html
https://www.cnblogs.com/findumars/p/9362036.html

首先我们要知道哪些类型可以用For In吧,下面就是:
for Element in ArrayExpr do Stmt; 数组
for Element in StringExpr do Stmt; 字符串
for Element in SetExpr do Stmt; 集合
for Element in CollectionExpr do Stmt; 集合
for Element in Record do Stmt; 结构体

一、遍历 TStrings
var
List: TStrings;
s: string;
begin
List := TStringList.Create;
List.CommaText := 'aaa,bbb,ccc';

for s in List do
ShowMessage(s);

List.Free;
end;

二、遍历数组
var
Arr: array[0..2] of Byte;
i: Integer;
b: Byte;
begin
for i := Low(Arr) to High(Arr) do
Arr[i] := Random(MAXBYTE);

for b in Arr do
ShowMessage(IntToStr(b));
end;

三、遍历子界
{例1}
var
sub: 0..9;
str: string;
begin
str := '';
for sub in [Low(sub)..High(sub)] do
str := str + IntToStr(sub);

ShowMessage(str); {0123456789}
end;

{例2}
type
TSub = 'A'..'G';
var
sub: TSub;
str: string;
begin
str := '';
for sub in [Low(sub)..High(sub)] do
str := str + sub;

ShowMessage(str); {ABCDEFG}
end;

{例3}
var
sub: Byte; {Byte 应该算是个 0..255 的子界}
num: Cardinal;
begin
num := 0;
for sub in [Low(sub)..High(sub)] do
Inc(num, sub);

ShowMessage(IntToStr(num)); {32640}
end;

四、遍历枚举
type
TEnum = (Red,Green,Blue);
var
enum: TEnum;
count: Integer;
begin
count := 0;
for enum in [Low(enum)..High(enum)] do
Inc(count);

ShowMessage(IntToStr(count)); {3}
end;

五、遍历集合
type
TEnum = (Red,Green,Blue,Yellow);
TSet = set of TEnum;
var
set1: set of TEnum;
set2: TSet;
elem: Tenum;
count: Integer;
begin
set1 := [Red, Yellow];
count := 0;
for elem in set1 do Inc(count);
ShowMessage(IntToStr(count)); {2}

set2 := [Red..Yellow];
count := 0;
for elem in set2 do Inc(count);
ShowMessage(IntToStr(count)); {4}
end;

六、遍历字符串
var
str: string;

c:string; //c: Char;
begin
str := 'ABCD';
for c in str do
ShowMessage(c);
end;