这两段代码有什么区别

cpp

string f(int x,int i=0,string s=string(""))
{
    if(x==0) return string("0");
    do{
        if(x&1) 
        {
            s=(i==1? "2" : "2(" +f(i)+ ")") + (s=="" ? "": "+")+s;
            /*
                string s1=s;
                if(i==1) s="2";
                else s= "2(" + f(i) + ")";
                if(s!="") s+="+";
                s+=s1; 
            */
        }
    }while(++i,x>>=1);
    return s;
}