大数相乘

给定两个数据“1234”与“3456”

#include <iostream>
#include <string>
#include <vector>
#include <stdlib.h>
#include <assert.h>
using namespace std;
struct bigcheng2
{
	string a;
	string b;
	string result_str;
};
//void reverse_data( string &data)；//字符串反转
//void multiply2(bigcheng2 &tempcheng2);//字符串模拟相乘
void reverse_data( string &data)
{
	char temp = '0';
	int start=0;
	int end=data.size()-1;
	assert( data.size()&& start <= end );
	while ( start < end )
	{
		temp = data[start];
		data[start++] = data[end];
		data[end--] = temp;
	}
}
void multiply2(bigcheng2 &tempcheng2)
{
	reverse_data(tempcheng2.a);//字符串反转
	reverse_data(tempcheng2.b);
	int c=0;
	string temp(tempcheng2.a.size()+tempcheng2.b.size(),'0');//将temp全部初始化为0字符
	for (unsigned int i=0;i<tempcheng2.a.size();i++)
	{
		unsigned int j;
		for (j=0;j<tempcheng2.b.size();j++)
		{
			c+=temp[i+j]-'0'+(tempcheng2.a[i]-'0')*(tempcheng2.b[j]-'0');//注意temp[i+j]可能保存有上一次计算的结果
			temp[i+j]=(c%10)+'0';//将结果转换为字符
			c=c/10;
		}
		while(c)
		{
			temp[i+j++]+=c%10;//temp里已存字符
			c=c/10;
		}
	}
	for (int i=temp.size()-1;i>=0;i--)
	{
		if (temp[i]!='0')
			break;
		else
			temp[i]='\0';
	}
	reverse_data(temp);//结果?字á?符¤?串??反¤??转áa
	tempcheng2.result_str=temp;
}
int main()
{
       bigcheng2 tempcheng2;
       string a,b;
       cin>>a>>b;
       tempcheng2.a=a;
       tempcheng2.b=b;
       multiply2(tempcheng2);
       cout<<tempcheng2.result_str<<endl;
       system("pause");
       return 0;
}

大数相加

bool check(char *p)
{
	if (!p)
	{
		return 1;
	}
	int i=0;
	while(p[i]!='\0') 
	{
		if (p[i]<'0'||p[i]>'9')
		{
			return 1;
		}
		else ++i;
	}
	return 0;//合法
}
char* bigadd(char *p1,char *p2)
{
	if (check(p1)||check(p2))
	{
		throw exception("Invalid input!");
	}
	int len1=strlen(p1);
	int len2=strlen(p2);
	int len3=max(len1,len2)+1;
	char *p3=new char[len3+1];
	memset(p3,'0',len3);
	p3[len3]='\0';
	int index1=len1-1,index2=len2-1,index3=len3-1;
	int carry=0;
	while(index1>=0&&index2>=0)
	{
		int num=p1[index1--]-'0'+p2[index2--]-'0'+carry;
		if (num>=10)
		{
			carry=1;
			num-=10;
		}
		else
			carry=0;
		p3[index3--]=num+'0';
	}
	while(index1>=0)
	{
		int num=p1[index1--]-'0'+carry;
		if (num>=10)
		{
			carry=1;
			num-=10;
		}
		else
			carry=0;
		p3[index3--]=num+'0';
	}
	while(index2>=0)
	{
		int num=p1[index2--]-'0'+carry;
		if (num>=10)
		{
			carry=1;
			num-=10;
		}
		else
			carry=0;
		p3[index3--]=num+'0';
	}
	p3[index3]=carry?'1':'0';
	return p3;
}