C++结构体报错问题

Question

定义分数结构体Per，重载Per相加符号，相加时化简。

struct Per
{
    int son, mom;
};

int gcd(int a, int b){
    int r, ok = 1, out;
    while(ok){
        r = a % b;
        if(r == 0){
            ok = 0;
            out = b;
        } else {
            a = b;
            b = r;
        }
    }
    return out;
}//最大公约数
int hj(int a, int b, int i){
    a = a / gcd(a, b);
    b = b / gcd(a, b);
    if(i) return b;
    else return a;
}//分子分母化简
Per operator + (const Per& a, const Per& b){
    int son = a.son * b.mom + a.mom * b.son;
    int mom = a.mom * b.mom;
    return Per(hj(son, mom, 0), hj(son, mom, 1));
}

ostream& operator << (ostream& out, const Per& p){
    out << p.son << "/" << p.mom;
    return out;
}

报错 no matching function for call to 'Per::Per(int, int)'

######查阅信息竞赛教材，发现刘汝佳在使用Point结构体时可以直接使用Point(int, int)，所以没有头绪

两个分数Per相加，化简，输出.son / .mom

Answer 1

没有相应的构造函数
结构体修改如下：

struct Per
{
    int son, mom;
    Per(){son=0;mom=0;}
    Per(int a,int b){son=a;mom=b;}
};