“运算符”的C模糊过载

ex1.cpp: In function ‘int main(int,char**)’:
ex1.cpp:35:13: error: ambiguous overload for ‘operator+’ in ‘a + 4’
ex1.cpp:35:13: note: candidates are:
ex1.cpp:35:13: note: operator+(int,int) <built-in>
In file included from ex1.cpp:3:0:
Fraccao.h:41:9: note: Fraccao operator+(const Fraccao&,const Fraccao&)
ex1.cpp:38:13: error: ambiguous overload for ‘operator+’ in ‘4 + a’
ex1.cpp:38:13: note: candidates are:
ex1.cpp:38:13: note: operator+(int,const Fraccao&)

班级：

class Fraccao {
    int numerador;
    int denominador;

public:
    Fraccao(int num = 0,int deno = 1) : numerador(num),denominador(deno) {}

    Fraccao & operator+=(const Fraccao &fra);

    Fraccao & operator*=(const Fraccao &fra);

    operator int() const;

    const Fraccao & operator++();
    const Fraccao operator++(int);

    string getAsString() const;
};

Fraccao operator +(const Fraccao &a,const Fraccao &b);
ostream & operator<<(ostream & saida,const Fraccao & fra);

在我的主要：

void func(int n) {
    cout << n; // 
}

int main(int argc,char** argv) {
    //...
    d = a + b;
    const Fraccao h(7,3);
    func(h);

    return 0;
}