UVa-10106-Product

AOAPC I: Beginning Algorithm Contests (Rujia Liu) :: Volume 1. Elementary Problem Solving :: Big Number

 

// 10106 - Product
#include <iostream>
#include <cstring>
//#include <cstdio>
#define MAXN 1000
using namespace std;
 
char A[MAXN], B[MAXN];
int a[MAXN], b[MAXN], c[MAXN];
 
int main(void)
{
    //freopen("in.txt", "r", stdin);
    //freopen("out.txt", "w", stdout);
 
    int lenA, lenB, carry, index, t, i, j, k, n;
    while(cin >> A >> B)
    {
        lenA = strlen(A);
        lenB = strlen(B);
        memset(a, 0, sizeof(a));
        memset(b, 0, sizeof(b));
        memset(c, 0, sizeof(c));
 
        for(i=lenA-1, k=0; i>=0; i--, k++)
            a[k] = A[i] - '0';
        for(i=lenB-1, k=0; i>=0; i--, k++)
            b[k] = B[i] - '0';
 
        index = 0;
        for(i=0; i<=lenA; i++)
        {
            carry = 0;
            t = index;
            for(j=0; j<=lenB; j++)
            {
                carry += a[i] * b[j];
                c[t] += carry % 10;
                carry /= 10;
                if(c[t] > 9) // !!!
                {
                    carry += c[t] / 10;
                    c[t] %= 10;
                }
                t++;
            }
            index++;
        }
 
        n = MAXN-1;
        while(n>0 && !c[n])      // 特别注意结果为零的情况！！！
            n--;                // 数组不能越界到-1！！！
        for(i=n; i>=0; i--)      // 同时必须输出一个零！！！
            cout << c[i];
        cout << endl;
    }
 
    return 0;
}