51nod 1027大数乘法

题目链接：51nod 1027大数乘法

直接模板了。

 #include<cstdio>
 #include<cstring>
 using namespace std;
 const int N = ;
 const int DLEN = ;
 const int mod = ;
 int alen, blen;
 int ans_len;
 char a1[N], b1[N];
 int a[], b[];
 int ans[];

 void BigInt(const char s[], int (&c)[], int &len){
     memset(c, , sizeof(c));
     int L = strlen(s);
     len = L / DLEN;
     if(L%DLEN) len++;
     int cnt = ;
     for(int i = L-; i >=  ; i -= DLEN){
         int k = i - DLEN + ;
         if(k < ) k = ;
         int t = ;
         for(int j = k; j <= i; ++j)
             t = t *  + s[j] - '';
         c[cnt++] = t;
     }
 }
 void multi(){
     int i, j;
     for(i = ; i < alen; ++i){
         int up = ;
         for(j = ; j < blen; ++j){
             int t = a[i] * b[j] + ans[i+j] + up;
             up = t / mod;
             ans[i+j] = t % mod;
         }
         if(up != )
             ans[i+j] = up;
     }
     ans_len = alen + blen;
     while(ans[ans_len-] ==  && ans_len > )
         ans_len--;

     printf("%d", ans[ans_len-]);
     for(i = ans_len-; i >= ; i--)
         printf("%04d", ans[i]);
     puts("");
 }
 int main(){
     scanf("%s%s", a1, b1);
     BigInt(a1, a, alen);
     BigInt(b1, b, blen);
     multi();
     return ;
 }