大数乘法模板

#include <iostream>
#include <stdio.h>
#include <string.h>
#include <vector>
#include <algorithm>
#include <string>
using namespace std;
string s1,s2;
string add(string a,string b)
{
string s;
int i=0,j=0,l=0;
int m,ans=0,k;
while(a[i]&&b[j])
{
m=a[i]-'0'+b[j]+ans-'0';
ans = m / 10;
s += (m%10+'0');
i++;
j++;
}
if(i==a.size())
{
while(i != b.size())
{
m = ans + b[i] - '0';
ans = m / 10;
s += m % 10 + '0';
i++;
}
if(ans) s += ans + '0';
}
else if(i==b.size())
{
while(i != a.size())
{
m = ans + a[i] - '0';
ans = m / 10;
s += m % 10 + '0';
i++;
}
if(ans) s += ans + '0';
}
return s;
}
void dashuchengfa()
{
int i,j,k=0,ans,num,w;
string anss="0",ss[10000];
for(i=0; i<s1.size(); i++)
{
for(w=0; w<i; w++)
ss[i]+='0';
for(j=0; j<s2.size(); j++)
{
num=(s1[i]-'0')*(s2[j]-'0')+k;
ans=num%10;
k=num/10;
ss[i]+=(ans+'0');
}
if(k!=0)
ss[i]+=(k+'0');
k=0;
}
for(i=0; i<s1.size(); i++)
anss=add(anss,ss[i]);
reverse(anss.begin(),anss.end());
cout<<anss<<endl;
}
int main()
{
//freopen("a.txt","r",stdin);
// freopen("aa.txt","w",stdout);
while(cin>>s1>>s2)
{
reverse(s1.begin(),s1.end());
reverse(s2.begin(),s2.end());
dashuchengfa();
}
return 0;
}