Convert decimal to binary in big number - c++

Question

I want to create a big number with 128 bit.
When I convert the string decimal to binary and set bit to the new data QInt :__int64 a[2], it only true for a small number (about 10 digits).
This is my code: http://codepad.org/HmYqMQme
#include<iostream>
#include<stdio.h>
#include<string>
using namespace std;
//new data
class QInt
{
private:
__int64 a[2];
public:
void Get()
{
cout << a[0] << endl;
cout << a[1] << endl;
}
QInt()
{
a[0] = 0;
a[1] = 0;
}
//the funtion get the string binary of a[1]
char* GetQInt(char *A);
//the devide two of string decimal
char* Div2(char *Str);
//the funtion set bit to a[0] and a[1]
void Setbit(int i, int bit);
//con vert decimal to binary
QInt ConvertDecimalToBinary(char *De, char *Bi);
};
//the funtion get the string binary of a[1]
char *QInt::GetQInt(char *A)
{
for (int i = 0; i < 64; i++)
{
if (((a[1] >> i) & 1) != 0)
{
A[63 - i] = 49;
}
else
{
A[63 - i] = 48;
}
}
return A;
}
// the funtion set bit to a[0] and a[1]
void QInt:: Setbit(int i, int bit)
{
//if i<64 we set bit to a[1]
if (i < 64)
{
if (bit==1)
{
a[1]=(1 << i) | a[1];
}
}//similar to a[1]
else
{
if (bit == 1)
a[0]=(1 << i) | a[0];
}
}
//the devide two of string decimal
char*QInt:: Div2(char *Str)
{
char Arr[100];
int n = strlen(Str);
int a = 0;//lay phan du
int i = 0;
int j = 0;
while (Str[i] == 0)
{
i++;
}
for (i; i < n; i++)
{
int c = Str[i] - 48 + a * 10;
a = c % 2;
Arr[j] = c / 2 + 48;
j++;
}
Arr[i] = '\0';
for (i = 0; i < strlen(Arr); i++)
{
Str[i] = Arr[i];
}
Str[i] = '\0';
return Str;
}
//con vert decimal to binary
QInt QInt::ConvertDecimalToBinary(char *De,char *Bi)
{
int bit;
int i = 127;
int lenth = strlen(De);
while (1)
{
//variable h use to count the number 0 of the string decimal,if h=lenth,exit
int k = 0;
int h = 0;
while (De[k])
{
if (De[k] == '0')
h++;
k++;
}
if (h == lenth)
break;
else
{
bit = (De[lenth - 1] - 48) % 2;
Bi[i] = bit + 48;
Setbit(127 - i, bit);
De = Div2(De);
i--;
}
}
Bi[128] = NULL;
return *this;
}
int main()
{
char s[100];
char b[200];
char c[200];
for (int i = 0; i < 128; i++)
{
b[i] = 48;
}
cout << "Please enter a string : ";
gets_s(s, 99);
QInt a;
a.ConvertDecimalToBinary(s, b);
a.Get();
a.GetQInt(c);
for (int i = 0; i < 64; i++)
cout << b[i];
cout << endl;
for (int i = 64; i < 128; i++)
cout << b[i];
cout << endl;
for (int i = 0; i < 64; i++)
{
cout << c[i];
}
cout << endl;
system("pause");
return 0;
}

Answer 1

If i==100, what do you think (1 << i) does? What should it do? And why are you ignoring a[0] in GetQInt ?
In general, you have quite a few problems. You're not comfortable with std::string, and making a mess of the char* everywhere. You're not clearly articulating (not even to yourself) what methods are supposed to be doing. You're putting mathods in a class that are unrelated to the class. Even worse, some of those methods redefine the name a ! That is very confusing.