Question: How can I pad out a vector with 0's if it is not a multiple of 8 bytes? 
In the following code I work out the offset and add to the vector to make sure it always has 8 values. I would like to pad this out with 0's and I am wondering what is the most efficient way to do this.

For example:

Input: **4444** 

With padding: **4444000000000000**

The code I have so far is:

```
if ((vector1.size() % 8) != 0)
{
  for (std::vector<unsigned char>::iterator itr = vector1.begin(); itr != vector1.end(); itr ++)
  {
    vector1.push_back(fmod(vector1.size(), 8));

    if(vector1.size() == 8)
      break;
  }
}

```

Answer: 
What's wrong with the trivial

```
while (vector1.size() % 8){
    vector1.push_back(0);
}

```

which will append zeros until the number of elements is a multiple of 8?

The potential for re-allocation is a red herring here given how you're making up the size.
How about:

```
constexpr std::size_t ceil_to_multiple(std::size_t n, std::size_t mul)
{
    return (n + mul - 1) / mul * mul;
}

```

and then

```
vector1.resize(ceil_to_multiple(vector1.size(), 8), 0);

```