UVA 465 Overflow

练习C++bign类高精度，这一题数据中含有前导0，必须在重载=号时处理一下，而且必须以char类型的数组输入，一开始我用bign类输入，会报错的，我WA了至少30多次。

#include <iostream>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <string>
#include <algorithm>
#include <climits>
using namespace std;

const int MAXN = 40000;
const int INF = 2147483647;

char str1[MAXN], str2[MAXN];

struct bign
{
	int len, s[MAXN];
	bign ()
	{
		memset(s, 0, sizeof(s));
		len = 1;
	}
	bign (int num) {*this = num;}
	bign (const char *num) { *this = num ;}
	bign operator = (const char* num)
	{
		for(int i = 0; num[i] == '0'; num++) ; //去前导0，很重要。 
		len = strlen(num);
		for(int i = 0; i < len; i++)
		{
			s[i] = num[len-i-1] - '0';
		}
		return *this;
	}
	bign operator = (int num)
	{
		char s[MAXN];
		sprintf(s, "%d", num);
		*this = s;
		return *this;
	}
    bign operator + (const bign& b) const  
    {  
        bign c;  
        c.len = 0;  
        for(int i = 0, g = 0; g || i < max(len, b.len); i++)  
        {  
            int x = g;  
            if(i < len)  
                x += s[i];  
            if(i < b.len)  
                x += b.s[i];  
            c.s[c.len++] = x % 10;  
            g = x / 10;  
        }  
        return c;  
    }
	void clean()
	{
		while(len > 1 && !s[len-1]) len--;
	}
	bign operator * (const bign &b) const
	{
		bign c;
		c.len = len + b.len;
		for(int i = 0; i < len; i++)
		{
			for(int j = 0; j < b.len; j++)
			{
				c.s[i+j] += s[i] * b.s[j];
			}
		}
		for(int i = 0; i < c.len; i++)
		{
			c.s[i+1] += c.s[i] / 10;
			c.s[i] %= 10;
		}
		c.clean();
		return c;
	}
	bign operator += (const bign &b)
	{
		*this = *this + b;
		return *this;
	}
	bool operator < (const bign &b)
	{
		if(len != b.len) return len < b.len;
		for(int i = len-1; i >= 0; i--)
		{
			if(s[i] != b.s[i]) return s[i] < b.s[i];
		}
		return false;
	}
	bool operator > (const bign &b)
	{
		if(len != b.len) return len > b.len;
		for(int i = len-1; i >= 0; i--)
		{
			if(s[i] != b.s[i]) return s[i] > b.s[i];
		}
		return false;
	}
	bool operator == (const bign &b)
	{
		return !(*this > b) && !(*this < b);
	}
	string str() const
	{
		string res = "";
		for(int i = 0; i < len; i++) res = char(s[i]+'0') + res;
		if(s[len-1] == 0) res = "";
		if(res == "") res = "0";
		return res;
	}
};

istream& operator >> (istream &in, bign &x)
{
	string s;
	in >> s;
	x = s.c_str();
	return in;
}

ostream& operator << (ostream &out, bign &x)
{
	out << x.str();
	return out;
}

int main()
{
	char ope;
	bign a, b;
    while(~scanf("%s", str1))
    {
		scanf(" %c", &ope);
		scanf("%s", str2);
		printf("%s %c %s\n", str1, ope, str2);
		a = str1, b = str2;
		if(a > INF) printf("first number too big\n");
		if(b > INF) printf("second number too big\n");
		if(ope == '+' && a+b > INF) printf("result too big\n");
		else if(ope == '*' && a*b > INF) printf("result too big\n");
    }  
    return 0;    
}