C++: Convert ushort, uint and ulong to vector<uchar> - c++

Question

I'm building a numeric class to work with 1 to 8 bytes. The idea is: input the value by a string or a char*, then the program convert it to unsigned short, unsigned int or unsigned long, according to the string size (I've used stringstream to conversion, this part is ok). After the program separa the value in bytes, storing them in a vector<unsigned char>. To output the number, the program convert the vector<unsigned char> to unsigned short, unsigned int or unsigned long, according to the number of bytes and then convert to string.
The problem is: the program is storing/showing a value different to the inputed.
Here's the full code:
typedef unsigned char uchar;
typedef unsigned short ushort;
typedef unsigned int uint;
typedef unsigned long ulong;
class Num
{
private:
vector<uchar> x;
ushort len;
template<typename T>
string str()
{
T val = 0;
for(ushort i = 0; i < len; i++)
{
val += x[i] * pow(256, i);
}
stringstream res;
res << val;
return res.str();
}
template<typename T>
void set(string a)
{
T val;
stringstream(a) >> val;
x.resize(0);
len = 0;
while(val > 255)
{
x.push_back((T)(val % 256));
len++;
val = (T)(val / 256);
}
len++;
for(ushort i = 0; i <= len / 2; i++)
{
uchar aux = x[i];
x[i] = x[len - 1 - i];
x[x.size() - 1 - i] = aux;
}
}
public:
Num()
{
x.resize(0);
len = 0;
}
Num(const Num& other)
{
*this = other;
}
friend bool operator>(const Num& l, const Num& r)
{
for(uchar i = l.len - 1; i >= 0; i--)
{
if(l.x[i] != r.x[i])
return (l.x[i] > r.x[i]);
}
}
friend bool operator<(const Num& l, const Num& r)
{
return r > l;
}
friend bool operator>=(const Num& l, const Num& r)
{
return !(l < r);
}
friend bool operator<=(const Num& l, const Num& r)
{
return !(l > r);
}
friend bool operator==(const Num& l, const Num& r)
{
return l >= r && l <= r;
}
friend bool operator!=(const Num& l, const Num& r)
{
return !(l == r);
}
Num& operator=(const string& l)
{
string a = l;
if(a.size() <= 4)
{
set<ushort>(a);
}
else if(a.size() <= 9)
{
set<uint>(a);
}
else
{
set<ulong>(a);
}
return *this;
}
Num& operator=(const char* l)
{
return (*this = string(l));
}
string get()
{
if(len == 0)
return "0";
if(len <= 2)
{
return str<ushort>();
}
else if(len <= 4)
{
return str<uint>();
}
else
{
return str<ulong>();
}
}
friend ostream& operator<<(ostream& os, Num& l)
{
return os << l.get();
}
friend istream& operator>>(istream& is, Num& l)
{
string x;
is >> x;
l = x;
return is;
}
};
int main()
{
Num x;
cout << "Entrada: ";
cin >> x;
cout << "Saida: "<< x << endl;
system("pause");
return 0;
}
The result can be:
Entrada: 572648319
Saida: 3136023423