POJ1001 且适合带小数点大数的幂（R^N）

/** \function calculator R^N * * \param * \param * \return * */#include <iostream>#include <vector>#include <string>using namespace std;//big number multiplication.//str1 is the first number.//str2 is the second number.//return str1*str2string BigNumberMulti(const string& str1,const string& str2){        string product_str;        vector<int> product_number,product_number_reverse;        //reset every member of vector product_number to 0.        int i=0,limit=str1.size()+str2.size()-1;        for(i=0;i!=limit;i++)        {            product_number.push_back(0);        }        //multiplication content and the product is stored in product_number.        string::const_iterator iter_str1,iter_str2;        vector<int>::iterator iter_int;        vector<int>::difference_type bit_move=0;//multiplication move one bit by once        for(iter_str2=str2.begin();iter_str2!=str2.end();iter_str2++)        {            for(iter_str1=str1.begin(),iter_int=product_number.begin()+bit_move;iter_str1!=str1.end();iter_str1++,iter_int++)            {                *iter_int=*iter_int+(*iter_str2-'0')*(*iter_str1-'0');            }            bit_move++;        }        //transform ints to chars,product_number to product_str.        int remainder_now=0,remainder_pre=0;        vector<int>::reverse_iterator reverse_iter_int;        for(reverse_iter_int=product_number.rbegin();reverse_iter_int!=product_number.rend();reverse_iter_int++)        {            remainder_now=(*reverse_iter_int+remainder_pre)%10;            product_number_reverse.push_back(remainder_now);            remainder_pre=(*reverse_iter_int+remainder_pre)/10;        }        while(remainder_pre!=0)        {            product_number_reverse.push_back(remainder_pre%10);            remainder_pre=remainder_pre/10;        }        for(reverse_iter_int=product_number_reverse.rbegin();reverse_iter_int!=product_number_reverse.rend();reverse_iter_int++)        {            product_str.push_back('0'+*reverse_iter_int);        }        return product_str;}/** \round calculator R^n * * \param int n * \return string * */string power(const string& R_int,int n){    if(n==0)    {        string str0("1");        return str0;    }    else    {        string str1=power(R_int,n/2);        if(n%2==0)return BigNumberMulti(str1,str1);        else return BigNumberMulti(BigNumberMulti(str1,str1),R_int);    }}/** \function transform R_double to R_int * * \param * \param * \return * */class Two_Var{public:    string R_int;    int point_steps;};Two_Var R_transform(const string& R_double){    Two_Var temp;    string::const_iterator iter;    int point_position,po_pre=0;    for(iter=R_double.begin();iter!=R_double.end();iter++)    {        if(*iter=='.') break;        po_pre++;    }    point_position=R_double.size()-(po_pre+1);    if(point_position<1) point_position=0;    temp.point_steps=point_position;    string str_int;    for(iter=R_double.begin();iter!=R_double.end();iter++)    {        if(*iter!='.'&&*iter!='0') break;    }    for(;iter!=R_double.end();iter++)        if(*iter!='.') str_int.push_back(*iter);    temp.R_int=str_int;    return temp;}/** \add point(.) in N_int,meanwhile delete 0 at the end * * \param1 int type of the product * \param2 the position to insert point(.) * \return final perfect product * */string add_0andpoint(const string& product_str,int pointsteps){    string final_str;    string::const_iterator iter,iter1;    int flag=0;//0 shows have not added point,1 shows have added point.    if(product_str.size()>pointsteps)    {        iter1=product_str.begin()+product_str.size()-pointsteps;        for(iter=product_str.begin();iter!=product_str.end();)        {            if(flag==0&&iter==iter1)            {                final_str.push_back('.');                flag=1;            }            else            {                final_str.push_back(*iter);                iter++;            }        }    }    else    {        final_str.push_back('.');        flag=1;        int i=0;        for(i=1;i<pointsteps-product_str.size()+1;i++)            final_str.push_back('0');        for(iter=product_str.begin();iter!=product_str.end();iter++)            final_str.push_back(*iter);    }    //delete zeros of the end    string::reverse_iterator iter2,iter3;    for(iter2=final_str.rbegin();iter2!=final_str.rend();iter2++)        if(*iter2!='0') break;    for(iter3=final_str.rbegin();iter3!=final_str.rend();iter3++)        if(*iter3=='.') break;    if(iter3==final_str.rend()) return final_str;    string::difference_type zeros_mount=iter2-final_str.rbegin();    if(iter3>iter2)        final_str.erase(final_str.size()-zeros_mount,zeros_mount);    else if(iter3==iter2)        final_str.erase(final_str.size()-zeros_mount-1,zeros_mount+1);    if(final_str.size()==0) final_str="0";//if final_str is null,let it be "0";    return final_str;}int main(){    int N;//power    string R_double;//str input,the R of R^N    Two_Var twovar;    while (cin>>R_double>>N)    {        twovar=R_transform(R_double);        cout<<add_0andpoint(power(twovar.R_int,N),N*twovar.point_steps)<<endl;    }    return 0;}