假定用于分析的数据包含属性age。数据元组中age的值如下（按递增序）：13, 15, 16, 16, 19, 20, 20, 21, 22, 22, 25, 25, 25, 25, 30, 33, 33, 35, 35, 35, 35, 36, 40, 45, 46, 52, 70。使用c语言实现,使用ODBC连接数据库。实现如下功能（要求程序具有通用性）： (a) 使用按箱平均值平滑法对以上数据进行平滑，箱的深度为3。 (b) 使用按箱中值平滑法对以上数据进行平滑，箱的深度为3。 (c) 使用按箱边界值平滑法对以上数据进行平滑，箱的深度为3。

首先需要安装ODBC驱动程序，然后使用C语言编写程序连接数据库，读取数据并进行平滑处理。

以下是基本的程序框架：

#include <stdio.h>
#include <stdlib.h>
#include <sql.h>
#include <sqlext.h>

#define BUFFER_LEN 1024

int main(void)
{
    SQLHENV henv; // Environment handle
    SQLHDBC hdbc; // Connection handle
    SQLHSTMT hstmt; // Statement handle
    SQLRETURN retcode;
    char buffer[BUFFER_LEN];

    // Allocate environment handle
    retcode = SQLAllocHandle(SQL_HANDLE_ENV, SQL_NULL_HANDLE, &henv);
    if (retcode != SQL_SUCCESS && retcode != SQL_SUCCESS_WITH_INFO) {
        printf("SQLAllocHandle failed: %d\n", retcode);
        return EXIT_FAILURE;
    }

    // Set ODBC version
    retcode = SQLSetEnvAttr(henv, SQL_ATTR_ODBC_VERSION, (SQLPOINTER)SQL_OV_ODBC3, 0);
    if (retcode != SQL_SUCCESS && retcode != SQL_SUCCESS_WITH_INFO) {
        printf("SQLSetEnvAttr failed: %d\n", retcode);
        SQLFreeHandle(SQL_HANDLE_ENV, henv);
        return EXIT_FAILURE;
    }

    // Allocate connection handle
    retcode = SQLAllocHandle(SQL_HANDLE_DBC, henv, &hdbc);
    if (retcode != SQL_SUCCESS && retcode != SQL_SUCCESS_WITH_INFO) {
        printf("SQLAllocHandle failed: %d\n", retcode);
        SQLFreeHandle(SQL_HANDLE_ENV, henv);
        return EXIT_FAILURE;
    }

    // Connect to database
    retcode = SQLConnect(hdbc, (SQLCHAR *)"DataSourceName", SQL_NTS, (SQLCHAR *)"username", SQL_NTS, (SQLCHAR *)"password", SQL_NTS);
    if (retcode != SQL_SUCCESS && retcode != SQL_SUCCESS_WITH_INFO) {
        printf("SQLConnect failed: %d\n", retcode);
        SQLFreeHandle(SQL_HANDLE_DBC, hdbc);
        SQLFreeHandle(SQL_HANDLE_ENV, henv);
        return EXIT_FAILURE;
    }

    // Allocate statement handle
    retcode = SQLAllocHandle(SQL_HANDLE_STMT, hdbc, &hstmt);
    if (retcode != SQL_SUCCESS && retcode != SQL_SUCCESS_WITH_INFO) {
        printf("SQLAllocHandle failed: %d\n", retcode);
        SQLDisconnect(hdbc);
        SQLFreeHandle(SQL_HANDLE_DBC, hdbc);
        SQLFreeHandle(SQL_HANDLE_ENV, henv);
        return EXIT_FAILURE;
    }

    // Execute query and fetch data
    retcode = SQLExecDirect(hstmt, (SQLCHAR *)"SELECT age FROM table_name ORDER BY age", SQL_NTS);
    if (retcode != SQL_SUCCESS && retcode != SQL_SUCCESS_WITH_INFO) {
        printf("SQLExecDirect failed: %d\n", retcode);
        SQLFreeHandle(SQL_HANDLE_STMT, hstmt);
        SQLDisconnect(hdbc);
        SQLFreeHandle(SQL_HANDLE_DBC, hdbc);
        SQLFreeHandle(SQL_HANDLE_ENV, henv);
        return EXIT_FAILURE;
    }

    // Smooth data using moving average method with window size 3
    // TODO: Implement smoothing algorithm

    // Smooth data using median filter method with window size 3
    // TODO: Implement smoothing algorithm

    // Smooth data using boundary value method with window size 3
    // TODO: Implement smoothing algorithm

    // Free handles and disconnect from database
    SQLFreeHandle(SQL_HANDLE_STMT, hstmt);
    SQLDisconnect(hdbc);
    SQLFreeHandle(SQL_HANDLE_DBC, hdbc);
    SQLFreeHandle(SQL_HANDLE_ENV, henv);

    return EXIT_SUCCESS;
}

在上面的程序框架中，需要将 `DataSourceName`、`username` 和 `password` 替换为实际的数据库连接信息。

接下来分别实现三种平滑算法：

### 按箱平均值平滑法

void moving_average(double *data, int n, int window_size)
{
    int i, j;
    double sum;

    for (i = window_size / 2; i < n - window_size / 2; i++) {
        sum = 0.0;
        for (j = i - window_size / 2; j <= i + window_size / 2; j++) {
            sum += data[j];
        }
        data[i] = sum / window_size;
    }
}

### 按箱中值平滑法

void median_filter(double *data, int n, int window_size)
{
    int i, j, k, l, r, mid;
    double *window = (double *)malloc(window_size * sizeof(double));

    for (i = window_size / 2; i < n - window_size / 2; i++) {
        l = i - window_size / 2;
        r = i + window_size / 2;
        for (j = l; j <= r; j++) {
            window[j - l] = data[j];
        }
        for (j = 0; j < window_size - 1; j++) {
            for (k = j + 1; k < window_size; k++) {
                if (window[j] > window[k]) {
                    double temp = window[j];
                    window[j] = window[k];
                    window[k] = temp;
                }
            }
        }
        mid = window_size / 2;
        if (window_size % 2 == 0) {
            data[i] = (window[mid - 1] + window[mid]) / 2.0;
        } else {
            data[i] = window[mid];
        }
    }

    free(window);
}

### 按箱边界值平滑法

void boundary_value(double *data, int n, int window_size)
{
    int i, j, l, r;

    for (i = window_size / 2; i < n - window_size / 2; i++) {
        l = i - window_size / 2;
        r = i + window_size / 2;
        if (data[i] < data[l]) {
            data[i] = data[l];
        } else if (data[i] > data[r]) {
            data[i] = data[r];
        }
    }
}

最后在主程序中调用这三个函数即可：

// Execute query and fetch data
retcode = SQLExecDirect(hstmt, (SQLCHAR *)"SELECT age FROM table_name ORDER BY age", SQL_NTS);
if (retcode != SQL_SUCCESS && retcode != SQL_SUCCESS_WITH_INFO) {
    printf("SQLExecDirect failed: %d\n", retcode);
    SQLFreeHandle(SQL_HANDLE_STMT, hstmt);
    SQLDisconnect(hdbc);
    SQLFreeHandle(SQL_HANDLE_DBC, hdbc);
    SQLFreeHandle(SQL_HANDLE_ENV, henv);
    return EXIT_FAILURE;
}

// Fetch data
int n = 0;
double data[BUFFER_LEN];
while (SQLFetch(hstmt) == SQL_SUCCESS) {
    SQLGetData(hstmt, 1, SQL_C_DOUBLE, &data[n], sizeof(double), NULL);
    n++;
}

// Smooth data using moving average method with window size 3
moving_average(data, n, 3);

// Smooth data using median filter method with window size 3
median_filter(data, n, 3);

// Smooth data using boundary value method with window size 3
boundary_value(data, n, 3);