编写一个程序，要求如下： 1) 设计并实现自然数（MyNaturalNumbers）及整数（MyInteger）类。 2) 自然数及整数类至少能表示及处理20位自然数或整数数据。 3) 自然数及整数类能表示及处理任意位数的自然数或整数数据。（选作。第五章内容） 4) 自然数及整数类的设计应体现体系结构（即应设计实现完整的继承关系）。 5) 自然数及整数类应提供数据赋值、数据输出、加法计算、减法计算功能。

好的，以下是一个简单的实现：

class MyNaturalNumbers {
private:
    string value; // 自然数的值

public:
    MyNaturalNumbers() {
        value = "0";
    }

    MyNaturalNumbers(string _value) {
        value = _value;
    }

    MyNaturalNumbers& operator=(const MyNaturalNumbers& other) {
        value = other.value;
        return *this;
    }

    friend ostream& operator<<(ostream& os, const MyNaturalNumbers& obj) {
        os << obj.value;
        return os;
    }

    MyNaturalNumbers operator+(const MyNaturalNumbers& other) const {
        string result = "";
        int carry = 0;
        int i = value.size() - 1;
        int j = other.value.size() - 1;

        while (i >= 0 || j >= 0 || carry != 0) {
            int x = (i >= 0) ? value[i] - '0' : 0;
            int y = (j >= 0) ? other.value[j] - '0' : 0;
            int sum = x + y + carry;
            result += (sum % 10) + '0';
            carry = sum / 10;
            i--;
            j--;
        }

        reverse(result.begin(), result.end());
        return MyNaturalNumbers(result);
    }

    MyNaturalNumbers operator-(const MyNaturalNumbers& other) const {
        string result = "";
        int borrow = 0;
        int i = value.size() - 1;
        int j = other.value.size() - 1;

        while (i >= 0 || j >= 0) {
            int x = (i >= 0) ? value[i] - '0' : 0;
            int y = (j >= 0) ? other.value[j] - '0' : 0;
            int diff = x - y - borrow;

            if (diff < 0) {
                diff += 10;
                borrow = 1;
            } else {
                borrow = 0;
            }

            result += diff + '0';
            i--;
            j--;
        }

        reverse(result.begin(), result.end());
        return MyNaturalNumbers(result);
    }
};

class MyInteger : public MyNaturalNumbers {
private:
    bool is_negative; // 是否为负数

public:
    MyInteger() {
        is_negative = false;
    }

    MyInteger(string _value) : MyNaturalNumbers(_value) {
        is_negative = false;
    }

    MyInteger& operator=(const MyInteger& other) {
        MyNaturalNumbers::operator=(other);
        is_negative = other.is_negative;
        return *this;
    }

    friend ostream& operator<<(ostream& os, const MyInteger& obj) {
        if (obj.is_negative) {
            os << "-";
        }
        os << obj.value;
        return os;
    }

    MyInteger operator+(const MyInteger& other) const {
        if (!is_negative && !other.is_negative) {
            return MyInteger(MyNaturalNumbers::operator+(other).value);
        } else if (is_negative && other.is_negative) {
            MyInteger result(MyNaturalNumbers::operator+(other).value);
            result.is_negative = true;
            return result;
        } else if (!is_negative && other.is_negative) {
            MyInteger positive_other(other.value);
            positive_other.is_negative = false;
            return MyInteger(MyNaturalNumbers::operator-(positive_other).value);
        } else {
            MyInteger positive_this(value);
            positive_this.is_negative = false;
            return MyInteger(other.operator-(positive_this).value);
        }
    }

    MyInteger operator-(const MyInteger& other) const {
        if (!is_negative && !other.is_negative) {
            if (*this >= other) {
                return MyInteger(MyNaturalNumbers::operator-(other).value);
            } else {
                MyInteger result(other.operator-(MyNaturalNumbers::operator*(*this)).value);
                result.is_negative = true;
                return result;
            }
        } else if (is_negative && other.is_negative) {
            if (*this >= other) {
                MyInteger result(MyNaturalNumbers::operator-(other).value);
                result.is_negative = true;
                return result;
            } else {
                return MyInteger(other.operator-(MyNaturalNumbers::operator*(*this)).value);
            }
        } else if (!is_negative && other.is_negative) {
            MyInteger positive_other(other.value);
            positive_other.is_negative = false;
            return MyInteger(MyNaturalNumbers::operator+(positive_other).value);
        } else {
            MyInteger positive_this(value);
            positive_this.is_negative = false;
            return MyInteger(positive_this.operator-(other).value);
        }
    }

    bool operator>=(const MyInteger& other) const {
        if (is_negative && !other.is_negative) {
            return false;
        } else if (!is_negative && other.is_negative) {
            return true;
        } else if (is_negative && other.is_negative) {
            MyInteger positive_this(value);
            MyInteger positive_other(other.value);
            positive_this.is_negative = false;
            positive_other.is_negative = false;
            return positive_other >= positive_this;
        } else {
            if (value.size() > other.value.size()) {
                return true;
            } else if (value.size() < other.value.size()) {
                return false;
            } else {
                int i = 0;
                while (i < value.size() && value[i] == other.value[i]) {
                    i++;
                }
                if (i == value.size()) {
                    return true;
                } else if (value[i] > other.value[i]) {
                    return true;
                } else {
                    return false;
                }
            }
        }
    }

    MyInteger operator-() const {
        MyInteger result(*this);
        result.is_negative = !is_negative;
        return result;
    }
};

这个实现中，`MyNaturalNumbers` 类表示自然数，`MyInteger` 类继承自 `MyNaturalNumbers`，表示整数。其中，`MyNaturalNumbers` 实现了自然数的加法和减法，`MyInteger` 实现了整数的加法、减法和取相反数操作。在加法和减法的实现中，我们需要根据两个操作数的正负情况分别进行处理。在 `MyInteger` 类中，我们使用了继承来实现体系结构。