求Sum[pow((1/i),2){i,1,n}]：
#include <iostream>
using namespace std;
int main()
{
    double i,n,sum=0;
    cout<<"input n="<<endl;
    cin>>n;
    for(i=1;i<=n;i++)
    {
        sum=sum+(1/i)*(1/i);
    }
    cout<<"sum="<<sum<<endl;
    return 0;
}


用对象指针访问对象数组：
#include <iostream>
using namespace std;
class Rectangle
{
    public:
        void setRec(int len,int wid);
        void disp();
    private:
        int length,width;
};
void Rectangle::setRec(int len,int wid)
{
    length=len;
    width=wid;
}
void Rectangle::disp()
{
    cout<<"length="<<length<<"\t"<<"width="<<width<<endl;
}
int main()
{
    Rectangle rec[2];     //定义类Rectangle的对象数组rec
    Rectangle *pr;        //定义pr指向类Rectangle的对象指针变量
    rec[0].setRec(20,30); //调用元素rec[0]的成员函数setRec
    rec[1].setRec(40,60); //调用元素rec[1]的成员函数setRec
    pr=rec;               //将对象数组rec的起始地址赋给pr
                          //调用pr说指向的对象数组rec中第一个元素
    pr->disp();           //函数disp，即rec[0].disp()
    pr++;                 //对象指针变量pr加1
                          //即指向下一个元素rec[1]的地址
                          //调用pr所指向的对象rec数组中第2个元素的
    pr->disp();           //函数disp，rec[1].disp
    return 0;
}


论文中一些数据做多元线性回归（R软件）：
x1<-c(5160.3,5425.1,5888.8,6279.9,6907.1,7702.8,8472.2,9500.5,10493.6,11769.5,13785.8)
x2<-c(6388.1,6765.1,7188,7828,8591.8,9367.8,10510.4,12299.5,14002,16042.2,18885.3) x3<-c(1235,1473.6,1495.7,1607.5,1544.4,1607.4,1634.4,2081,2033.2,2442.8,2970.9)
x4<-c(3743.5,4280.8,4739.9,5075.8,5779.5,6765.9,8018.2,9197.4,10787.3,12292.9,13058)
y<-c(1790,1854,1857,1948,2017,2092,2197,2608,2937,3119,2645)
x<-cbind(x1,x2,x3,x4)
>x

lm<-lm(y~x)
>lm

>summary(lm)



那个是暴力的穷举法，另外我不知道你的第二问什么意思，麻烦详细说明

应该是10^9吧？和int的范围有关，在C语言中int的范围是-2147483648 ~ +2147483647  

今天上班中的一些数据，同时用R软件做的一元回归分析：

>x=matrix(c(0.1,42,0.11,43,0.12,45,0.13,45,0.14,45,0.15,47.5,0.16,49,0.17,53,0.18,50,0.2,55,0.21,55,0.23,60),nrow=12,ncol=2,byrow=T,dimnames=list(1:12,c("C","E")))
> outputcost=as.data.frame(x)
> plot(outputcost$C,outputcost$E)

很显然这些点基本上（但并不精确地）落在一条直线上。
下面在之前数据录入的基础上做回归分析：
> lm.sol = lm(E~C,data = outputcost)
> summary(lm.sol)



对上面的summary进行分析：
常数项=28.083，变量的系数=132.899
得到回归方程：y =28.083+132.899x
由于回归模型建立使用的是最小二乘法 ,而最小二乘法只是一种单纯的数学方法 ,存在着一定的缺陷 ,即不论变量间有无相关关系或有无显著线性相关关系 ,用最小二乘法都可以找到一条直线去拟合变量间关系。所以回归模型建立之后 ,还要对其进行显著性检验 ：在上面的结果中sd(常数项）=1.567，sd(变量系数)=9.606。而对应于两个系数的P 值6.27e-09 和7.59e-08，故是非常显著的。
关于方程的检验，残差的标准差=1.309。相关系数的平方R2 =0.9503。关于F 分布的P 值为7.585e-08，也是非常显著的。

将得到的直线方程画在散点图上，
> abline(lm.sol)
得到散点图及相应的回归直线：

下面分析残差：
> y.res=residuals(lm.sol);
> plot(y.res)
得到残差图：

从残差图可以看出，第8个点有些反常，这样用程序将第8 个点的残差标出：
> text(8,y.res[8],labels=8,adj=1.2)

这个点可能有问题，下面做简单处理，去掉该样本点：
> i=1:12;
> outputcost2=as.data.frame(x[i!=8,])
> lm2=lm(E~C,data=outputcost2)
> summary(lm2)

由结果分析，去掉第8个点之后，回归方程系数变化不大，R2 相关系数有所提高，并且p-值变小了，这说明样本点8可以去掉。

结果分析后得到的新模型：
>x2=matrix(c(0.1,42,0.11,43,0.12,45,0.13,45,0.14,45,0.15,47.5,0.16,49,0.18,50,0.2,55,0.21,55,0.23,60),nrow=11,ncol=2,byrow=T,dimnames=list(1:11,c("C","E")))
> outputcost=as.data.frame(x2)
> plot(outputcost$C,outputcost$E)
> lm.sol = lm(E~C,data = outputcost)
> summary(lm.sol)

> abline(lm.sol)
得到最后的散点图和回归直线:

得到回归方程：y =28.124+131.293x
Q.E.D

输出1~5的阶乘值：
#include <iostream>
using namespace std;
int fac(int n);
int main()
{
for(int i=1;i<=5;i++)
{
cout<<i<<"!="<<fac(i)<<endl;
}
system("pause");
return 0;
}
int fac(int n)
{
static int f=1;
f=f*n;
return f;
}


辗转相除求最大公因子（递归）：
#include<iostream>
using namespace std;
int fun(int n,int m)
{
if(n%m==0) return m;
else{return fun(m,n%m);}
}
int main()
{
int a,b,c;
cin>>a>>b;
if(a<b){c=a;a=b;b=c;}
cout<<fun(a,b)<<endl;
system("pause");
return 0;
}

除了递归，循环也是一个办法

1,1,2,3,5,8,13,21...这一列输的规律是:从第三个数开始，每个数为其前面两个数的和，写出计算这列数前20个数的和：
#include <iostream>
using namespace std;
int Fibonacci(int N)
{
if(N <= 2)
return 1;
else
return Fibonacci(N - 1) + Fibonacci(N - 2);
}
int main()
{
int sum=0,n;
cout<<"input n=";
cin>>n;
for(int i = 1; i <= n; i++)
{
sum=sum+Fibonacci(i);
}
cout<<"sum="<<sum<<endl;
return 0;
}


> install.packages("plotrix")
> library(plotrix)
> pieval=c(2,4,6,8)
> pielabels=c("讨厌3D饼图","反对3D饼图","无所谓","喜欢3D饼图")
> pie3D(pieval,radius=0.9,labels=pielabels,explode=0.1,main="3D饼图用户态度表")



我没编过人机界面的软件，测试一下程序：
#include <windows.h>
/* Declare Windows procedure */
LRESULT CALLBACK WindowProcedure (HWND, UINT, WPARAM, LPARAM);
/* Make the class name into a global variable */
char szClassName[ ] = "WindowsApp";
int WINAPI WinMain (HINSTANCE hThisInstance,
HINSTANCE hPrevInstance,
LPSTR lpszArgument,
int nFunsterStil)
{
HWND hwnd; /* This is the handle for our window */
MSG messages; /* Here messages to the application are saved */
WNDCLASSEX wincl; /* Data structure for the windowclass */
/* The Window structure */
wincl.hInstance = hThisInstance;
wincl.lpszClassName = szClassName;
wincl.lpfnWndProc = WindowProcedure; /* This function is called by windows */
wincl.style = CS_DBLCLKS; /* Catch double-clicks */
wincl.cbSize = sizeof (WNDCLASSEX);
/* Use default icon and mouse-pointer */
wincl.hIcon = LoadIcon (NULL, IDI_APPLICATION);
wincl.hIconSm = LoadIcon (NULL, IDI_APPLICATION);
wincl.hCursor = LoadCursor (NULL, IDC_ARROW);
wincl.lpszMenuName = NULL; /* No menu */
wincl.cbClsExtra = 0; /* No extra bytes after the window class */
wincl.cbWndExtra = 0; /* structure or the window instance */
/* Use Windows's default color as the background of the window */
wincl.hbrBackground = (HBRUSH) COLOR_BACKGROUND;
/* Register the window class, and if it fails quit the program */
if (!RegisterClassEx (&wincl))
return 0;
/* The class is registered, let's create the program*/
hwnd = CreateWindowEx (
0, /* Extended possibilites for variation */
szClassName, /* Classname */
"PCG's Very Simple Windows Application", /* Title Text */
WS_OVERLAPPEDWINDOW, /* default window */
CW_USEDEFAULT, /* Windows decides the position */
CW_USEDEFAULT, /* where the window ends up on the screen */
544, /* The programs width */
375, /* and height in pixels */
HWND_DESKTOP, /* The window is a child-window to desktop */
NULL, /* No menu */
hThisInstance, /* Program Instance handler */
NULL /* No Window Creation data */
);
/* Make the window visible on the screen */
ShowWindow (hwnd, nFunsterStil);
/* Run the message loop. It will run until GetMessage() returns 0 */
while (GetMessage (&messages, NULL, 0, 0))
{
/* Translate virtual-key messages into character messages */
TranslateMessage(&messages);
/* Send message to WindowProcedure */
DispatchMessage(&messages);
}
/* The program return-value is 0 - The value that PostQuitMessage() gave */
return messages.wParam;
}
/* This function is called by the Windows function DispatchMessage() */
LRESULT CALLBACK WindowProcedure (HWND hwnd, UINT message, WPARAM wParam, LPARAM lParam)
{
switch (message) /* handle the messages */
{
case WM_DESTROY:
PostQuitMessage (0); /* send a WM_QUIT to the message queue */
break;
default: /* for messages that we don't deal with */
return DefWindowProc (hwnd, message, wParam, lParam);
}
return 0;
}