} } }

    C++/C The variable in the LOOP STRUCT

    添加时间:2013-5-9 点击量:

     1 #include<iostream>
    
    2 using namespace std;
    3 void main()
    4 {
    5 for(int i=0;i<5;i++)
    6 cout<<i<< ;
    7 cout<<endl;
    8 for(int i=5;i<10;i++)
    9 cout<<i<< ;
    10 cout<<endl;
    11 }
    12
    13 --------------------Configuration: fgyt - Win32 Debug--------------------
    14 Compiling...
    15 d.cpp
    16 E:\Program Files\Microsoft Visual Studio\MyProjects\fgyt\d.cpp(9) : error C2374: i : redefinition; multiple initialization
    17 E:\Program Files\Microsoft Visual Studio\MyProjects\fgyt\d.cpp(6) : see declaration of i
    18 Error executing cl.exe.
    19
    20 d.obj - 1 error(s), 0 warning(s)


     



     1 /when I compile this program in Visual Studio 2012/
    
    2
    3 #include<iostream>
    4 #include<conio.h>
    5 using namespace std;
    6 void main()
    7 {
    8 for(int i=0;i<5;i++)
    9 cout<<i<< ;
    10 cout<<endl;
    11 for(i=5;i<10;i++)
    12 cout<<i<< ;
    13 cout<<endl;
    14 getch();
    15 }
    16
    17 1>------ 已启动生成: 项目: ConsoleApplication9, 设备: Debug Win32 ------
    18 1> 源.cpp
    19 1>c:\users\wkl7123\documents\visual studio 2012\projects\consoleapplication9\consoleapplication9\源.cpp(50): error C2065: “i”: 未声明的标识符
    20 1>c:\users\wkl7123\documents\visual studio 2012\projects\consoleapplication9\consoleapplication9\源.cpp(51): error C2065: “i”: 未声明的标识符
    21 ========== 生成: 成功 0 个,失败 1 个,新 0 个,跳过 0 个 ==========


    So I know, loop variable will disappear after the loop end in Visual Studio 2012, but not in VC 6.0



     1 //More...
    
    2 #include<iostream>
    3 using namespace std;
    4 void main()
    5 {
    6 for(int i=0;i<5;i++)
    7 {
    8 int a=3;
    9 cout<<i<< ;
    10 }
    11 cout<<endl;
    12 for(i=5;i<10;i++)
    13 cout<<i<< ;
    14 cout<<endl;
    15 //cout<<a=<<a<<endl;
    16 }



    This is a program, its right though nearly nothing useful. But please stare at this sentence “int a=3;”it will be executed every loop, but system think its right, because every a will disapear when a loop end. So its easy to know when I add cout<<a=<<a<<endl; in the end of the problem, system will say 




    a: Undeclared identifier.




     To sum up,in Visual Studio 2012, Loop variable will disappear after all the loop end. But the variavle defined in the loop struct will disappear after a single loop end. However in VC6.0 the Loop variable will disappear when the function end. That is to say, 




    
    
    for(int i=0;i<5;i++)
    
    {...}

    
    

        VC 6.0
    
    <====equal===>


    int i;
    
    for(i=0;i<5;i++)

    {...}


    //I think Visual Studio 2012s way is better.

    原来,再大的房子,再大的床,没有相爱的人陪伴,都只是冰冷的物质。而如果身边有爱人陪伴,即使房子小,床小,也觉得无关紧要,因为这些物质上面有了爱的温度,成了家的元素。—— 何珞《婚房》#书摘#
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