/*两个大数相乘：char* multiply(char*,char*)。给了两个字符串，每个都是代表了一个很长的10进制表示的数， 比如 String str1 = "23456789009877666555544444"； String str2 = "346587436598437594375943875943875"， 最后求出它们的乘积。 不用jdk的数学运算包BigInteger.或者类似的包。*/#include<string>
#include<iostream>
#include<stdio.h>using namespace std;
string strPlusAsNum(string str1,string str2);string ZeroNum(int num){string result="";for(int i=0;i<num;i++){result+="0";}return result;
}
char * itoa_m(int n){char* arrBuff=NULL;int radix=10;char tmp[33];char* tp = tmp;int i;unsigned v;int sign;char* sp;if (radix > 36 || radix <= 1){
//        __set_errno(EDOM);//return 0;radix=10;}sign = (radix == 10 && n < 0);if (sign)v = -n;elsev = (unsigned)n;while (v || tp == tmp){i = v % radix;v = v / radix;if (i < 10)*tp++ = i+'0';else*tp++ = i + 'a' - 10;}if (arrBuff == 0){arrBuff=(char*)malloc((tp-tmp)+sign+1);}sp = arrBuff;if (sign)*sp++ = '-';while (tp > tmp)*sp++ = *--tp;*sp = 0;return arrBuff;
}int main(){//    string str1="2345678900987766554411223301",str2="346587436598437594375943875943875";
string str1="1234",str2="1234";cout<<"============"<<endl;cout<<"Biginteger 相乘运算"<<endl;cout<<"============"<<endl;cout<<"输入Num1=";cin>>str1;cout<<"输入Num2=";cin>>str2;string result;int wei1=strlen(str1.data());int wei2=strlen(str2.data());string * calcOneBit=new string[wei2];for(int i=0;i<wei2;i++){calcOneBit[i]+=str2.data()[wei2-i-1];int n1=atoi(calcOneBit[i].data());calcOneBit[i]="";//清空int str1_jinwei=0;string temp;for(int j=0;j<wei1;j++){//进行一位与str1的计算结果 保存到calcOneBit[i]中temp=str1.data()[wei1-j-1];int n2=atoi(temp.data());int n=n1*n2;n+=str1_jinwei;if(n>=10){str1_jinwei=n/10;n=n%10;}else{str1_jinwei=0;}temp=calcOneBit[i];char *ccc=itoa_m(n);calcOneBit[i]=ccc; free(ccc);calcOneBit[i]+=temp;cout<<"calcOneBit["<<i<<"]="<<calcOneBit[i].data()<<endl;}if(str1_jinwei>0){temp=calcOneBit[i];char * cc=itoa_m(str1_jinwei);calcOneBit[i]=cc;free(cc);calcOneBit[i]+=temp;cout<<"&& calcOneBit["<<i<<"]="<<calcOneBit[i].data()<<endl;}}for(int i=0;i<wei2;i++){if(i>0)calcOneBit[i]+=ZeroNum(i);cout<<" "<<i<<" "<< calcOneBit[i].data()<<endl;}result=calcOneBit[0];for(int i=0;i < wei1 - 1;i++){result=strPlusAsNum(result,calcOneBit[i+1]);}cout<<"========================"<<endl;cout<<""<<str1.data()<<" * "<<str2.data()<<" = "<<result.data()<<endl;cout<<"========================"<<endl;return 0;
}string strPlusAsNum(string str1,string str2){int size1=strlen(str1.data());int size2=strlen(str2.data());int size=size1>size2 ? size1 : size2;int jinwei=0;string result="",temp="";for(int i=0;i<size;i++){int n1,n2,n;//n1if(i<size1){string temp2;temp2=str1.data()[size1-i-1];n1=atoi(temp2.data());}else{n1=0;}//n2if(i<size2){string temp2;temp2=str2.data()[size2-i-1];n2=atoi(temp2.data());}else{n2=0;}//Plus nn=n1+n2;n+=jinwei;if(n>=10){jinwei=n/10;n=n%10;}else{jinwei=0;}//n to stringchar * cc=itoa_m(n);temp=result;result=cc;free(cc);result+=temp;}if(jinwei>0){temp=result;char * cc=itoa_m(jinwei);result=cc;free(cc);result+=temp;}return result;
}