C++/CLI学习入门(二):控制与循环 …

一、基本控制结构

ISO/ANSIC++中的控制与循环全部适用于C++/CLI。下例展示了C++/CLI控制台程序中的控制循环：

例子：基本循环控制- - - - - - - - - - - -- - - - <<== 华丽的分割线::开始==>> [Ex3_15.cpp] - - - - - -- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -- - -// Ex3_15.cpp : main project file.
#include "stdafx.h"

using namespace System;

int main(array<System::String ^>^args)
{
wchar_t letter;

Console::Write(L"Enter a letter:");
letter = Console::Read();

if(letter>='A')
if(letter<='Z')
{
Console::WriteLine(L"You entered a captial letter.");
return 0;
}

if(letter>='a')
if(letter<='z')
{
Console::WriteLine(L"You entered a small letter.");
return 0;
}

Console::WriteLine(L"You did not enter a letter.");
return 0;
}- - - - - - - - - - - - - - - - <<==华丽的分割线 ::结束==>>[Ex3_15.cpp] - - - - - - - - - - - - - - - - - - - - - - - - - - -- - - - - - - - - - - - - - - -

letter被声明为wchar_t类型，映射为C++/CLI中的System::Char类型，它具有一些特殊的功能，其中包括将字符代码转换为大写和小写的函数：Char::ToUpper（）和Char::ToLower()，被转换的函数作为参数被传递给它:

wchar_t uppercaseLetter = Char::ToUpper(letter);

此外还包括检测字母是否大写或小写的函数:IsUpper()和IsLower()，因此上例可改为

wchar_t letter;
wchar_t upper;

Console::Write(L"Enter a letter:");
letter = Console::Read();
upper = Char::ToUpper(letter);

if(upper>='A' &&upper<='Z')
Console::WriteLine(L"You entered a {0} letter.",Char::IsUpper(letter) ? "Capital":"Small");
else
Console::WriteLine(L"You entered a small letter.");

Console::ReadKey()函数用于测试按键，并将结果存储在ConsoleKeyInfo类对象里。该类有3个可访问属性用于帮助确定被按下的键是哪个或哪些键。属性Key识别被按下的键是哪个，属性KeyChar是被按键的Unicode字符码，属性Modifiers表示Shift,Alt,Ctrl键的按位组合，它是定义在System命名空间中的枚举类型ConsoleModifiers的常量，包括Shift\Alt\Control。

应该注意的是，在C++/CLI中枚举常量在用作数值之前必须被显示的强制转换为值类型（整数类型）

例子：使用Console::ReadKey()函数- - - - - -- - - - - - - - - - <<==华丽的分割线 ::开始==>>[Ex3_16.cpp] - - - - - - - - - - - - - - - - - - - - - - - - - - -- - - - - - - - - - - - - - - -// Ex3_16.cpp : main projectfile.

#include "stdafx.h"

using namespace System;

int main(array<System::String ^>^args)
{
ConsoleKeyInfo keyPress;

Console::WriteLine(L"Press a key combination - press Escape toquit.");
do{
keyPress = Console::ReadKey(true);
Console::Write(L"You pressed");
if(safe_cast<int>(keyPress.Modifiers)>0)
Console::Write(L" {0}", keyPress.Modifiers);
Console::WriteLine(L" {0} which is the {1} character",keyPress.Key, keyPress.KeyChar);
}while(keyPress.Key != ConsoleKey::Escape);
return 0;
}- - - - - - - - - - - - - - - - <<==华丽的分割线 ::结束==>>[Ex3_16.cpp] - - - - - - - - - - - - - - - - - - - - - - - - - - -- - - - - - - - - - - - - - - -

该程序的输入示例如下：

Press a key combination - press Escape to quit.
You pressed Enter which is the character
You pressed Spacebar which is the character
You pressed Spacebar which is the character

从输出中可以看出，当不只一个键被按下时，用一条语句就可以得到所有的键。这是因为Modifiers枚举类型是用FlagsAttribute属性定义的，该属性表明这种枚举类型是一组唯一的位标志。这使得该枚举类型的变量可以由若干与在一起的标志位组成，而Write()或WriteLine()函数可以识别并输出各标志位。

二、for each循环

以例子开始

- - - - - - - - - - - - - - - - <<==华丽的分割线 ::开始==>>[Ex3_17.cpp] - - - - - - - - - - - - - - - - - - - - - - - - - - -- - - - - - - - - - - - - - - -// Ex3_17.cpp : main projectfile.

#include "stdafx.h"

using namespace System;

int main(array<System::String ^>^args)
{
int volwels = 0;
int consonants = 0;
String^ proverb = L"A nod is as good as a wink to a blindhorse.";

for each(wchar_t ch in proverb)
{
if(Char::IsLetter(ch))
{
ch = Char::ToLower(ch);
switch(ch)
{
case 'a': case 'e': case 'i': case 'o': case 'u':
++volwels;
break;

default:
++consonants;
break;
}
}
}

Console::WriteLine(proverb);
Console::WriteLine(L"The proverb contains {0} volwels and {1}consonants.",
volwels, consonants);
return 0;
}- - - - - - - - - - - - - - - - <<==华丽的分割线 ::结束==>>[Ex3_17.cpp] - - - - - - - - - - - - - - - - - - - - - - - - - - -- - - - - - - - - - - - - - - -

输出为：

A nod is as good as a wink to a blind horse.
The proverb contains 14 volwels and 18 consanants.

注意：由于proverb字符串中的字符都是Unicode字符，因此用wchar_t（映射为Char类型）类型的变量来存储这些字符。变量ch为循环内的局部变量。