UVA465:Overflow

WA了三次；仅仅是因为输出输入数据时，先去了了前导0.罪过啊！！

#include<iostream>
#include<string>
#include<limits>
#include<sstream>
using namespace std;

inline string reverse(const string a)
{
    string t(a.rbegin(), a.rend());
    return t;
}
string operator + (const string& a, const string& b)
{
    string sum = "";
    int c = 0, i = 0;
    for( ; i < a.size() && i < b.size(); ++i)
    {
        c += a[i] - '0' + b[i] - '0';
        sum += c%10 + '0';
        c /= 10;
    }
    while(i < a.size())
    {
        c += a[i] - '0';
        sum += c % 10 + '0';
        c /= 10;
        ++i;
    }
    while(i < b.size())
    {
        c += b[i] - '0';
        sum += c % 10 + '0';
        c /= 10;
        ++i;
    }
    if(c)
        sum += 1 + '0';
    return sum;
}
string operator +=(string& a, string& b)
{
    return a = a+b;
}
string operator * (string& a, string& b)
{
    if(a.size() > b.size())
    {
        string t(a);
        a = b;
        b = t;
    }
    string tot = "0";
    for(int i = 0; i != a.size(); ++i)
    {
        string sum(i, '0');
        int c = 0;
        for(int j = 0; j != b.size(); ++j)
        {
            c += (a[i] - '0') * (b[j] - '0');
            sum += (c % 10 + '0');
            c /= 10;
        }
        while(c)
        {
            sum += (c%10 + '0');
            c /= 10;
        }
        tot += sum;
    }
    return tot;
}

string del_pre_zero(string& a)
{
    int i = 0;
    for(; a[i] == '0' && i != a.size(); ++i);
    if(i == a.size())
        a = "0";
    else
    {
        string b(a.begin()+i, a.end());
        a = b;
    }
    return a;
}

inline bool is_bigger(const string& a, const string& b)
{
    if(a.size() != b.size())
        return a.size() > b.size();
    return a > b;
}
int main()
{
    string a, b, c, sum;
    int n = (numeric_limits<int>::max)();
    stringstream ss;
    ss << n;
    string max_int;
    ss >> max_int;
    //cout << max_int << endl;//2147483647
    while(cin >> a >> c >> b)//getline(cin, a), a != "0")
    {
        cout << a << " " << c << " " << b << endl;
        a = del_pre_zero(a);
        b = del_pre_zero(b);
        if(is_bigger(a, max_int))
            cout << "first number too big" << endl;
        if(is_bigger(b, max_int))
            cout << "second number too big" << endl;
        sum = "";
        a = reverse(a);
        b = reverse(b);
        if(c == "+")
            sum = a + b;
        else if(c == "*")
            sum = a * b;
        sum = reverse(sum);
        sum = del_pre_zero(sum);
        if(is_bigger(sum, max_int))
            cout << "result too big" << endl;
    }
    return 0;
}

#include<iostream>
#include<string>
#include<sstream>

using namespace std;

string del_pre_zero(const string& a)
{
    int i = 0;
    for(; a[i] == '0' && i != a.size(); ++i);
    if(i == a.size())
        return "0";
    string t(a.begin()+i, a.end());
    return t;
}
bool is_not_small(const string& a, const string& b)
{
    if(a.size() != b.size())
        return a.size() > b.size();
    return a >= b;
}

string reverse(const string& a)
{
    string t(a.rbegin(), a.rend());
    return t;
}
string operator - (const string& a, const string& b)
{
    //cout << "a: " << a << "  " << "b: " << b << endl;
    string result = "";
    string x(a), y(b);
    bool flag = true;
    if(!is_not_small(a, b))
    {
        flag = false;
        string t(x);
        x = y;
        y = t;
    }
    x = reverse(x);
    y = reverse(y);
    int i, cur, c;
    i = cur = c = 0;
    for(; i < y.size(); ++i)
    {
        cur = x[i] - y[i] + c;
        (cur < 0) ? (cur += 10, c = -1) : (c = 0);
        result +=(cur + '0');
    }
    while(i < x.size())
    {
        cur = x[i] - '0' + c;
        (cur < 0) ? (cur += 10, c = -1) : (c = 0);
        result += (cur + '0');
        ++i;
    }
    if(!flag)
    {
        string t = "-";
        t += result;
        result = t;
    }
    result = reverse(result);
    return del_pre_zero(result);
}

string operator -= (string& a, const string& b)
{
    return a = a - b;
}
string operator / (const string& a, const string& b)
{
    if(!is_not_small(a, b))
        return "0";
        if(a == b)
            return "1";
        string x(a), y(b);
    int count = 0;
    while(is_not_small(x, y))
    {
        x -= y;
        ++count;
    }
    stringstream ss;
    ss << count;
    string result = "";
    ss >> result;
    return result;
}
string operator % (const string& a, const string& b)
{
    if(!is_not_small(a, b))
        return a;
        if(a == b)
            return "0";
    string x(a), y(b);
    while(is_not_small(x, y))
    {
        x -= y;
       // cout << "***" << x << "***" << endl;
    }
    return x;
}

int main()
{
    string a, b, c, result;
    std::ios::sync_with_stdio(false);
    while(cin >> a >> c >> b, b != "0")
    {
        a = del_pre_zero(a);
        b = del_pre_zero(b);
        if(c == "%")
            result = a % b;
        else if(c == "/")
            result = a / b;
            //cout << a - b << endl;
        cout << result << endl;
    }
    return 0;
}