为什么这份代码会出现这样的问题？

/**
 * This file is for "Code Analysis Dev Team" private testing only.
 * DO NOT spread this beta cersion through PUBLIC CHANNELS.
 */

#define Test
#define High_Precision_Calc

#ifdef Test
#define UNKNOWN_CASES -1
#define SYSTEM_ERROR -2
#define APPLICATION_FAULT -3
#endif 

#ifdef High_Precision_Calc
#define private public
#define protected public 
#endif

#include <iostream>
#include <cstring> // Including for memset(). 
using namespace std;

class calculation
{
	public:
		int len;
		bool flag; // If n >= 0, flag = true. Or flag = false.
		short num[1000005]; // For 0 to 9 only, short is enough.
	calculation()
	{ // Set at 0.
		len = 1, flag = true;
		memset(num, 0, sizeof num);
		return ;
	}
	calculation(int x)
	{ // Set at x. 
		len = 0, memset(num, 0, sizeof num);
		if(x >= 0) flag = true;
		else flag = false, x = -x;
		while(x > 0) num[++len] = x % 10, x /= 10;
		if(!len) len = 1; // If x = 0, we can't go into the while (line 39).
		return ;
	}
	calculation(string s)
	{ // Set at s. 
		if(s[0] == '-') flag = false, s = s.substr(1);
		else flag = true;
		len = s.size();
		for(int i = 1; i <= len; i++)
			num[i] = s[len - i] - '0';
		return ;
	}
	~calculation()
	{  /**
	    * In order not to take any risk, although we don't need, write a destructer is necessary.
	    * Set at 0.
	    */
		len = 1, flag = true;
		memset(num, 0, sizeof num);
		return ;
	}
};

// This is the unsigned calculating area.
bool unsigned_smaller(calculation a, calculation b)
{
	if(a.len != b.len) return a.len < b.len;
	for(int i = a.len; i >= 1; i--)
		if(a.num[i] != b.num[i])
			return a.num[i] < b.num[i];
	return false;
} 
bool unsigned_bigger(calculation a, calculation b)
{
	if(a.len != b.len) return a.len > b.len;
	for(int i = a.len; i >= 1; i--)
		if(a.num[i] != b.num[i])
			return a.num[i] > b.num[i];
	return false;
} 
bool unsigned_equal(calculation a, calculation b)
{
	if(a.len != b.len) return false;
	for(int i = 1; i <= a.len; i++)
		if(a.num[i] != b.num[i])
			return false;
	return true;
} 

// This is the signed calculating area.


/**
 * Because divide needs plus, minus and multiplicate three types of operators, 
 * so I put the divide calculating area here. 
 * This is the divide calculating area.
 */

signed main()
{
	calculation a(10), b(20);
	cout << unsigned_smaller(a, b) << endl;
	
	return 0;
}

使用软件：Dev-C++

编译器：TDM-GCC 4.9.2 64-bit Release