转载高精度加减乘除法

#include <iostream>

#include <string>

using namespace std;

inline int compare(string str1,string str2) {//相等返回0，大于返回1，小于返回-1

         if (str1.size()>str2.size()) return 1; //长度长的整数大于长度小的整数

    else if (str1.size()<str2.size()) return -1;

    else                              return str1.compare(str2); //若长度相等，则头到尾按位比较

}

string SUB_INT(string str1,string str2);

string ADD_INT(string str1,string str2) {//高精度加法

    int sign=1; //sign 为符号位

    string str;

    if (str1[0]=='-') {

        if (str2[0]=='-') {

            sign=-1;

            str=ADD_INT(str1.erase(0,1),str2.erase(0,1));

        } else {

            str=SUB_INT(str2,str1.erase(0,1));

        }

    } else {

        if (str2[0]=='-') {

            str=SUB_INT(str1,str2.erase(0,1));

        } else { //把两个整数对齐，短整数前面加0补齐

            string::size_type L1,L2;

            int i;

            L1=str1.size();

            L2=str2.size();

            if (L1<L2) {

                for (i=1;i<=L2-L1;i++) str1="0"+str1;

            } else {

                for (i=1;i<=L1-L2;i++) str2="0"+str2;

            }

            int int1=0,int2=0; //int2 记录进位

            for (i=str1.size()-1;i>=0;i--) {

                int1=(int(str1[i])-'0'+int(str2[i])-'0'+int2)%10;

                int2=(int(str1[i])-'0'+int(str2[i])-'0'+int2)/10;

                str=char(int1+'0')+str;

            }

            if (int2!=0) str=char(int2+'0')+str;

        }

    }

    //运算后处理符号位

    if ((sign==-1)&&(str[0]!='0')) str="-"+str;

    return str;

}

string SUB_INT(string str1,string str2) {//高精度减法

    int sign=1; //sign 为符号位

    string str;

    int i,j;

    if (str2[0]=='-') {

        str=ADD_INT(str1,str2.erase(0,1));

    } else {

        int res=compare(str1,str2);

        if (res==0) return "0";

        if (res<0) {

            sign=-1;

            string temp =str1;

            str1=str2;

            str2=temp;

        }

        string::size_type tempint;

        tempint=str1.size()-str2.size();

        for (i=str2.size()-1;i>=0;i--) {

            if (str1[i+tempint]<str2[i]) {

                j=1;

                while (1) {//zhao4zhong1添加

                    if (str1[i+tempint-j]=='0') {

                        str1[i+tempint-j]='9';

                        j++;

                    } else {

                        str1[i+tempint-j]=char(int(str1[i+tempint-j])-1);

                        break;

                    }

                }

                str=char(str1[i+tempint]-str2[i]+':')+str;

            } else {

                str=char(str1[i+tempint]-str2[i]+'0')+str;

            }

        }

        for (i=tempint-1;i>=0;i--) str=str1[i]+str;

    }

    //去除结果中多余的前导0

    str.erase(0,str.find_first_not_of('0'));

    if (str.empty()) str="0";

    if ((sign==-1) && (str[0]!='0')) str ="-"+str;

    return str;

}

string MUL_INT(string str1,string str2) {//高精度乘法

    int sign=1; //sign 为符号位

    string str;

    if (str1[0]=='-') {

        sign*=-1;

        str1 =str1.erase(0,1);

    }

    if (str2[0]=='-') {

        sign*=-1;

        str2 =str2.erase(0,1);

    }

    int i,j;

    string::size_type L1,L2;

    L1=str1.size();

    L2=str2.size();

    for (i=L2-1;i>=0;i--) { //模拟手工乘法竖式

        string tempstr;

        int int1=0,int2=0,int3=int(str2[i])-'0';

        if (int3!=0) {

            for (j=1;j<=(int)(L2-1-i);j++) tempstr="0"+tempstr;

            for (j=L1-1;j>=0;j--) {

                int1=(int3*(int(str1[j])-'0')+int2)%10;

                int2=(int3*(int(str1[j])-'0')+int2)/10;

                tempstr=char(int1+'0')+tempstr;

            }

            if (int2!=0) tempstr=char(int2+'0')+tempstr;

        }

        str=ADD_INT(str,tempstr);

    }

    //去除结果中的前导0

    str.erase(0,str.find_first_not_of('0'));

    if (str.empty()) str="0";

    if ((sign==-1) && (str[0]!='0')) str="-"+str;

    return str;

}

string DIVIDE_INT(string str1,string str2,int flag) {//高精度除法。flag==1时,返回商; flag==0时,返回余数

    string quotient,residue; //定义商和余数

    int sign1=1,sign2=1;

    if (str2 == "0") {  //判断除数是否为0

        quotient= "ERROR!";

        residue = "ERROR!";

        if (flag==1) return quotient;

        else         return residue ;

    }

    if (str1=="0") { //判断被除数是否为0

        quotient="0";

        residue ="0";

    }

    if (str1[0]=='-') {

        str1   = str1.erase(0,1);

        sign1 *= -1;

        sign2  = -1;

    }

    if (str2[0]=='-') {

        str2   = str2.erase(0,1);

        sign1 *= -1;

    }

    int res=compare(str1,str2);

    if (res<0) {

        quotient="0";

        residue =str1;

    } else if (res == 0) {

        quotient="1";

        residue ="0";

    } else {

        string::size_type L1,L2;

        L1=str1.size();

        L2=str2.size();

        string tempstr;

        tempstr.append(str1,0,L2-1);

        for (int i=L2-1;i<L1;i++) { //模拟手工除法竖式

            tempstr=tempstr+str1[i];

            tempstr.erase(0,tempstr.find_first_not_of('0'));//zhao4zhong1添加

            if (tempstr.empty()) tempstr="0";//zhao4zhong1添加

            for (char ch='9';ch>='0';ch--) { //试商

                string str;

                str=str+ch;

                if (compare(MUL_INT(str2,str),tempstr)<=0) {

                    quotient=quotient+ch;

                    tempstr =SUB_INT(tempstr,MUL_INT(str2,str));

                    break;

                }

            }

        }

        residue=tempstr;

    }

    //去除结果中的前导0

    quotient.erase(0,quotient.find_first_not_of('0'));

    if (quotient.empty()) quotient="0";

    if ((sign1==-1)&&(quotient[0]!='0')) quotient="-"+quotient;

    if ((sign2==-1)&&(residue [0]!='0')) residue ="-"+residue ;

    if (flag==1) return quotient;

    else         return residue ;

}

string DIV_INT(string str1,string str2) {//高精度除法,返回商

    return DIVIDE_INT(str1,str2,1);

}

string MOD_INT(string str1,string str2) {//高精度除法,返回余数

    return DIVIDE_INT(str1,str2,0);

}

int main() {

    char ch;

    string s1,s2,res;

    while (cin>>s1>>ch>>s2) {

        switch (ch) {

            case '+':res=ADD_INT(s1,s2);break;

            case '-':res=SUB_INT(s1,s2);break;

            case '*':res=MUL_INT(s1,s2);break;

            case '/':res=DIV_INT(s1,s2);break;

            case '%':res=MOD_INT(s1,s2);break;

            default :                   break;

        }

        cout<<res<<endl;

    }

    return(0);

}