大數乘法（模板）

#include<stdio.h>
#include<iostream>
#include<string.h>
#include<algorithm>
using namespace std;
char c[1000001];
void reverse(char * c)//字符串翻轉函數
{
    int len = strlen(c);
    for(int i=0; i<len/2; i++)
        swap(c[i],c[len-i-1]);
}
void multiplication(char * sa,char * sb,char * ans)//大數相乘函數
{
    int i,j,k,r;
     reverse(sa);reverse(sb);
     int len=strlen(sa);
    int len1=strlen(sb);
      for(i=0;i<len;i++)
        {
            k=0;
            for(j=0;j<len1;j++)
            {
                int sum;
                int t=(sa[i]-'0'+0)*(sb[j]-'0'+0)+k;
                if(ans[i+j]>47)
                    sum=ans[i+j]-'0'+t;
                else
                    sum=t;
                    k=sum/10;
                    ans[i+j]=(sum%10)+'0';
            }
            r=0;
            while(k)
            {
                int t;
                if(ans[i+j+r]>47)
                t = ans[i+j+r]-'0' + k;
                else
                t=k;
                 k=t/10 ;
                ans[i+j+r] = (t%10)+'0';
                r++;
            }

        }
       reverse(sa);reverse(sb);reverse(ans);
}

int main()
{
    char a[10001],b[10001];
    while(scanf("%s%s",a,b)!=EOF)
    {
        memset(c,0,sizeof(c));
       multiplication(a,b,c);
        cout<<a<<endl<<"  乘  "<<endl<<b<<endl<<"="<<endl;
        cout<<c<<endl;
    }
    return 0;
}