Trying to convert C++ binary array to hexadecimal then print results - c++

Question

I'm wanting to print an int array with 8 bytes and convert it to bin & hex with the output as such:
0 00000000 00
1 00000001 07
...
I've finished creating the binary convert function. I want to use the same function as the binary conversion -with an array, but check the left half with the right half and solve each different sided of the 8 bytes; left most -3 and right most is -7.
What am I doing wrong? I cannot figure out how to implement it and I know my hex function is all out of wack.
#include <iostream>
#include <string>
#include <math.h>
using namespace std;
const int num = 8; //may not be needed -added for hex
void Generatebinary(int arr[]);
void GeneratehexDec(int arr[]);
void print_binary(int arr[]); //haven't created yet
int main()
{
int arr[8] = { 0, 0, 0, 0, 0, 0, 0, 0 };
int i = 1;
while (i < 256)
{
Generatebinary(arr);
print_binary(arr); //not created yet
GeneratehexDec(arr);
i++;
}
}
void Generatebinary(int arr[])
{
for (int i = 7; i > 0; i--)
{
if (arr[i] == 1)
arr[i] = 0;
else if (arr[i] == 0)
{
arr[i] = 1;
break;
}
}
}
void GereatehexDec(int num)
{ //improper use
int a;
int i;
int answer[] = { };
a = num % 16;
i++;
answer[i] = num;
for (int i = num; i > 0; i--)
{
cout << answer[i];
}
cout << a;
}

Answer 1

First of all, you can't do int answer[] = { }; an array has to be pre-allocated (indicating how many elements it will store) or has to be dynamically allocated during run-time, then be freed, you have to manage your memory, not forget to deallocate... It's for this reason that Stroustrup tells you to not use arrays unless necessary. Use std::vector
void GereatehexDec(int num)
{ //improper use
int a = 0; // always initialize your variables
int i = 0; // is this i supposed to be the same as the i in the for loop below?
std::vector<int> answer;
a = num % 16;
i++; // this doesn't make sense
answer.at(i) = num;
for (int i = num; i > 0; i--) // what about the i variable you declared previously?
{
cout << answer.at(i);
}
cout << a;
}
Here's a template function that could help you (converts numbers into string hex)
template <typename I> std::string n2hexstr(I w, size_t hex_len = sizeof(I) << 1) {
static const char* digits = "0123456789ABCDEF";
std::string rc(hex_len, '0');
for (size_t i = 0, j = (hex_len - 1) * 4; i<hex_len; ++i, j -= 4)
rc[i] = digits[(w >> j) & 0x0f];
return "0x" + rc;
}
int main() {
std::cout << n2hexstr(127);
}