计一个类，用菜单选择用成员函数重载运算符或友元函数重载运算符，使对整型的运算符=、+、-、*、/ 适用于分数运算。要求： (1) 输出结果是最简分数(可以是带分数)； (2) 分母为1，只输出分子。

以下是一个实现上述要求的分数类的示例代码：

#include <iostream>
using namespace std;

class Fraction {
private:
    int numerator;   // 分子
    int denominator; // 分母

public:
    Fraction() {
        numerator = 0;
        denominator = 1;
    }

    Fraction(int num, int den) {
        numerator = num;
        denominator = den;
        simplify();
    }

    void simplify() {
        int gcd = getGCD(numerator, denominator);
        numerator /= gcd;
        denominator /= gcd;
        if (denominator < 0) {
            numerator = -numerator;
            denominator = -denominator;
        }
    }

    int getGCD(int x, int y) {
        if (y == 0) {
            return x;
        }
        return getGCD(y, x % y);
    }

    friend Fraction operator+(const Fraction& f1, const Fraction& f2) {
        int num = f1.numerator * f2.denominator + f2.numerator * f1.denominator;
        int den = f1.denominator * f2.denominator;
        return Fraction(num, den);
    }

    friend Fraction operator-(const Fraction& f1, const Fraction& f2) {
        int num = f1.numerator * f2.denominator - f2.numerator * f1.denominator;
        int den = f1.denominator * f2.denominator;
        return Fraction(num, den);
    }

    friend Fraction operator*(const Fraction& f1, const Fraction& f2) {
        int num = f1.numerator * f2.numerator;
        int den = f1.denominator * f2.denominator;
        return Fraction(num, den);
    }

    friend Fraction operator/(const Fraction& f1, const Fraction& f2) {
        int num = f1.numerator * f2.denominator;
        int den = f1.denominator * f2.numerator;
        return Fraction(num, den);
    }

    Fraction& operator=(const Fraction& other) {
        numerator = other.numerator;
        denominator = other.denominator;
        return *this;
    }

    friend ostream& operator<<(ostream& os, const Fraction& f) {
        if (f.denominator == 1) {
            os << f.numerator;
        } else if (abs(f.numerator) >= f.denominator) {
            int integer = f.numerator / f.denominator;
            int num = abs(f.numerator) % f.denominator;
            if (f.numerator < 0) {
                os << "-";
            }
            os << integer << " " << num << "/" << f.denominator;
        } else {
            os << f.numerator << "/" << f.denominator;
        }
        return os;
    }
};

int main() {
    Fraction f1(1, 3);
    Fraction f2(2, 5);
    Fraction f3 = f1 + f2;
    cout << f3 << endl; // output: 11/15
    f3 = f1 - f2;
    cout << f3 << endl; // output: 1/15
    f3 = f1 * f2;
    cout << f3 << endl; // output: 2/15
    f3 = f1 / f2;
    cout << f3 << endl; // output: 5/6
    return 0;
}

该示例代码中，Fraction 类重载了运算符+、-、*、/ 和=，并且还定义了一个友元函数重载运算符<<，用于输出 Fraction 类型的对象。在运算符重载函数中，需要注意将分数化简为最简分数，且要处理分母为1的情况和负数的情况。