Fixing iteration-type of for-loop.

The current loops rely on `auto` deduction or integer suffix for the type that may not be a correct iteration type and may produce conversion warnings all over places. Therefore, I propose to remove `auto` from the loops and use appropriate and explicit types or use explicit types to initialize the variable. In a long run, it would produce a bug-free code, and it would remove all warnings produced by compilers.

From
```cpp
for(auto d = 0u; d < t.size(); ++d)
{
...
}
```

To
```cpp
for(auto d = size_type{0}; d < t.size(); ++d)
{
...
}
```