UVa 465 - Overflow

　　题目大意：给一个表达式，判断两个运算数和结果是否超过int类型的最大值。

　　可以用double类型进行计算。

#include <cstdio>
#include <climits>

int main()
{
#ifdef LOCAL
    freopen("in", "r", stdin);
#endif
    char str1[300], str2[300], op;
    double a, b;
    while (scanf("%s %c %s", str1, &op, str2) != EOF)
    {
        printf("%s %c %s\n", str1, op, str2);
        double a, b, c;
        sscanf(str1, "%lf", &a);
        sscanf(str2, "%lf", &b);
        if (op == '+')  c = a + b;
        else if (op == '*')  c = a * b;
        if (a > INT_MAX)  printf("first number too big\n");
        if (b > INT_MAX)  printf("second number too big\n");
        if (c > INT_MAX)  printf("result too big\n");
    }
    return 0;
}

　　开始是用bignum类做的，可是一直WA，也不知道怎么回事，先贴上代码，以后在研究吧。

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

const int maxn = 300;

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 = (int num)
    {
        char s[maxn];
        sprintf(s, "%d", num);
        *this = s;
        return *this;
    }

    bign operator = (const char * num)
    {
        len = strlen(num);
        for(int i = 0; i < len; i++)
            s[i] = num[len-1-i] - '0';
        return *this;
    }

    bign operator + (const bign& b) const 
    {
        bign c;
        c.len = 0;
        int g = 0;
        for(int i = 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)
    {
        bign c;
        c.len = 0;
        int g = 0;
        for(int i = 0; i < len; i++)
        {
            int x = s[i] - g;
            if(i < b.len)   x -= b.s[i];
            if(x >= 0)   g = 0;
            else 
            {
                g = 1;
                x += 10;
            }
            c.s[c.len++] = x;
        }
        c.clean();
        return c;
    }

    bign operator * (const bign& b)
    {
        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-1; 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) const
    {
        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) const
    {
        return b < *this;
    }

    bool operator <= (const bign& b) const 
    {
        return !(b < *this);
    }

    bool operator >= (const bign& b) const
    {
        return !(*this < b);
    }

    bool operator == (const bign& b) const 
    {
        return !(b < *this) && !(*this < b);
    }

    bool operator != (const bign& b) const
    {
        return (b < *this) || (b > *this);
    }

    string str() const
    {
        string res = "";
        for(int i = 0; i < len; i++)
            res = (char)(s[i] + '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, const bign& x)
{
    out << x.str();
    return out;
}

int main()
{
#ifdef LOCAL
    freopen("in", "r", stdin);
#endif
    char op;
    bign a, b, c;
    while (cin >> a >> op >> b)
    {
        if (op == '+')  c = a + b;
        else if (op == '*')  c = a * b;
        cout << a << " " << op << " " << b << endl;
        if (a > INT_MAX)  printf("first number too big\n");
        if (b > INT_MAX)  printf("second number too big\n");
        if (c > INT_MAX)  printf("result too big\n");
    }
    return 0;
}