程序代码：

/*
命名法:
函数:蛇形命名
变量:小驼峰法
思路:定义一个结构体,包含字符串指针与和两个整型变量,一个记录小数点位置,一个记录数字末尾(小数点并不存放于字符串中)
*/
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <ctype.h>
#define BUFFER_SIZE_MAX 200

typedef struct {
    char *data;//指向字符串
    int pi;//数字末尾
    int decimalPi;//小数点位置
}FloatNum;

void float_square_calculattion(char *data, int pow);

int main() {
    char douleStr[200];
    int pow;
    while (scanf("%200s%d", douleStr, &pow) == 2)
        float_square_calculattion(douleStr, pow);
    return 0;
}

FloatNum *str_to_FloatNum(char *data);//将字符串转换为结构体
FloatNum *reverse(FloatNum *Object);//逆序
FloatNum *float_creat_image(const FloatNum *constData);//声明拷贝函数
FloatNum *float_operation(const FloatNum *dataNum, FloatNum *dataImage, FloatNum *resultContainer, int pow);//声明运算函数
void str_set_data(char *, char val, int num);

void float_square_calculattion(char *str, int pow) {
    if (*str == '-') {//如果为负则先打印负号,并跳过字符串中的负号
        putchar('-');
        ++str;
    }
    FloatNum *dataNum = str_to_FloatNum(str);
    FloatNum *dataImage = float_creat_image(dataNum);//创建dataNum的镜像文件
    FloatNum *resultContainer = (FloatNum *)malloc(sizeof(FloatNum));//创建一个结果容器
    resultContainer->data = (char *)malloc(BUFFER_SIZE_MAX);
    str_set_data(resultContainer->data, '0', BUFFER_SIZE_MAX);
    FloatNum *result = float_operation(dataNum, dataImage, resultContainer, pow);//由于不确定最后到底返回容器还是镜像文件,故用另一个指针接收
    int resultPi;//result的字符串偏移量
    if (result->data[0] != '0')
        for (resultPi = 0; resultPi < result->decimalPi; resultPi++)
            putchar(result->data[resultPi]);
    else
        resultPi = 1;
    if (result->decimalPi < result->pi)
        putchar('.');
    printf("%s\n", result->data + resultPi);
    free(dataNum);
    free(dataImage->data);
    free(dataImage);
    free(resultContainer->data);
    free(resultContainer);
}

FloatNum *str_to_FloatNum(char  *str) {
    FloatNum *temp = (FloatNum *)malloc(sizeof(FloatNum));
    temp->data = (char *)malloc(BUFFER_SIZE_MAX);
    int tempPi;
    for (tempPi = 0; str[tempPi] != '.' && str[tempPi]; tempPi++)
        temp->data[tempPi] = str[tempPi];
    temp->decimalPi = tempPi;
    if (str[tempPi]) {//判断字符串整数部分后面是小数点还是结束符
        ++str;
        while (str[tempPi])
            temp->data[tempPi] = str[tempPi++];
    }
    temp->data[tempPi--] = 0;
    if (temp->decimalPi <= tempPi)
        while (temp->data[tempPi] == '0')
            temp->data[tempPi--] = 0;
    temp->pi = tempPi;
    return temp;
}

FloatNum* reverse(FloatNum *Object) {
    char temp;
    for (int i = Object->pi, g = 0; g < i; g++, i--) {
        temp = Object->data[i];
        Object->data[i] = Object->data[g];
        Object->data[g] = temp;
    }
    return Object;
}

FloatNum *float_creat_image(const FloatNum *constData) {
    FloatNum *tempBuffer = (FloatNum *)malloc(sizeof(FloatNum));
    tempBuffer->data = (char *)malloc(BUFFER_SIZE_MAX);
    strcpy(tempBuffer->data, constData->data);
    tempBuffer->decimalPi = constData->decimalPi;
    tempBuffer->pi = constData->pi;
    str_set_data(tempBuffer->data + tempBuffer->pi + 2, '0', BUFFER_SIZE_MAX - 2 - tempBuffer->pi);
    return tempBuffer;
}

FloatNum *float_operation(const FloatNum *dataNum, FloatNum *dataImage, FloatNum *resultContainer, int pow) {
    int tempBuffer = 0;
    for (int dataPi = dataNum->pi; dataPi >= 0; dataPi--) {
        resultContainer->pi = dataNum->pi - dataPi;
        for (int imagePi = dataImage->pi; imagePi >= 0; imagePi--) {
            tempBuffer = (dataNum->data[dataPi] - '0') * (dataImage->data[imagePi] - '0');
            resultContainer->data[resultContainer->pi] += tempBuffer % 10;
            tempBuffer /= 10;
            while (resultContainer->data[resultContainer->pi] > '9') {
                resultContainer->data[resultContainer->pi] -= 10;
                tempBuffer++;
            }
            resultContainer->data[++resultContainer->pi] += tempBuffer;
            tempBuffer = 0;
        }
    }
    if (resultContainer->data[resultContainer->pi] != '0')
        resultContainer->data[resultContainer->pi + 1] = 0;
    else
        resultContainer->data[resultContainer->pi--] = 0;
    if (resultContainer->decimalPi)
        resultContainer->decimalPi = resultContainer->pi - dataNum->pi + dataNum->decimalPi - dataImage->pi + dataImage->decimalPi - 1;//计算小数点位置:容器末尾+1 分别减去 原数和镜像的末尾 + 1 - 二者小数点位置
    if (pow == 2)
        return reverse(resultContainer);
    str_set_data(dataImage->data, '0', dataImage->pi + 2);
    return float_operation(dataNum, reverse(resultContainer), dataImage, pow - 1);//进行递归调用,容器作为镜像,镜像清空数据作为容器
}
void str_set_data(char *str, char val, int num) {
    for (int i = 0; i < num; i++)
        str[i] = val;
}