C++分数表达式加减运算实现

C++11虽然有radio库，但用起来也没那么方便
代码简单易懂，就不注释了

 string fractionAddition(string expression) {
        expression.push_back('+');
        vector<int> fenzi;
        vector<int> fenmu;
        int i=expression[0]=='-'?0:-1,j=0;
        while(j<expression.size()){
            //cout<<i<<" "<<j<<endl;
            if(expression[j]=='/'){
                int t=atoi(expression.substr(i+1,j-i-1).c_str());
                if(i>=0&&expression[i]=='-') t*=-1;
                fenzi.push_back(t);
                i=j;
            }
            else if(expression[j]=='+'||(expression[j]=='-'&&j!=0)){
                fenmu.push_back(atoi(expression.substr(i+1,j-i-1).c_str()));
                i=j;
            }
            ++j;
        }
        int fm=1;
        int fz=0;
        for(int& f:fenmu) fm*=f;
        for(int i=0;i<fenzi.size();++i){
            //cout<<fenzi[i]<<" "<<fenmu[i]<<endl;
            fz+=fenzi[i]*fm/fenmu[i];
        }
        int _gcd=gcd(fz,fm);    //gcd函数需要C++17版本
        //cout<<fz<<" "<<fm<<" "<<_gcd<<endl;
        return to_string(fz/_gcd)+"/"+to_string(fm/_gcd);
    }