Concatenating wide character strings
Firstly, avoid the non-n versions of (w)str_ functions. You've got a buffer overflow just begging to happen here - if amount.length() &gt; 100 - 8, it'll overflow your buffer, causing undefined behaviour and general bad times. Use wcsncat instead:

static const unsigned kstrMax = 100;
wchar_t strAmount[kstrMax] = L"Amount: ";
wchar_t* ptr = wcsncat(strAmount, amount.c_str(), kstrMax - amount.length() - 1);


In fact, we have to be even more careful here, because there's still a bug in the above code (I left it in because I only caught it when modifying my example - it's easy to make mistakes). Say amount.length() &gt; kstrMax, then you'd think the value kstrMax - amount.length() would be below zero, but being unsigned, it will silently overflow, and will instead be some very large positive value, hence we could still easily overwrite the buffer size with this if amount is large enough.

static const unsigned kstrMax = 100;
unsigned currentBufferSize = kstrMax;
wchar_t strAmount[kstrMax] = L"Amount: ";
if(amount.length() &gt;= kstrMax - 8) {
    //find out the difference, remake your buffer and copy across
    currentBufferSize = newBufferSize;
}
wchar_t* ptr = wcsncat(strAmount, amount.c_str(), currentBufferSize - amount.length());


From the looks of it, the amount entered is meant to be a small numeric value. Never assume anything about input. Anything that a user touches must be sanitized before you blindly use it. 

std::wstring would make this fiddling about go away:

std::wstring strAmount("Amount: ");
strAmount += amount.c_str();
final.set(strAmount.c_str(), strAmount.size());