Win API wrong textbox output - winapi

Question

I've been tying to build a simple Win Api program (using CodeBlocks) and ran into a weird problem.
case WM_COMMAND:{
if (LOWORD(wParam) == Calculate) {
int A=0, ArrayReset = 0;
char textread[256];
SendMessage((HWND)Box1,(UINT) EM_GETLINE, (WPARAM)1, (LPARAM)&textread);
A = atoi(textread);
itoa(ArrayReset, textread, 10);
itoa(A, textread, 10);
SendMessage((HWND)Box1,(UINT) WM_SETTEXT, (WPARAM)1,(LPARAM)&textread);
(My program is a bit more complicated, but this is just to show the problematic point)
Now, what I expect the code to do is to read the value in Box1, convert it into integer, convert it back to char array, and print this array back on the same Box1. Basically, some converting with no difference in the end result.
However, there is this strange problem. The code works with single digit numbers just fine, but if I enter a number with more digits, like 12 or 356, I get 1200 and 3560 respectively. If the input number is bigger than a thousand, it works fine again.
Is this a problem because of my method of resetting array's value back to 0, or does it have to do something with the conversion processes?

Answer 1

There are some mistakes in this code.
For starters, (LPARAM)&textread should be either (LPARAM)textread or (LPARAM)&textread[0].
But more importantly, you are not preparing the EM_GETLINE message correctly:
lParam
A pointer to the buffer that receives a copy of the line. Before sending the message, set the first word of this buffer to the size, in TCHARs, of the buffer. For ANSI text, this is the number of bytes; for Unicode text, this is the number of characters. The size in the first word is overwritten by the copied line.
Try this instead:
case WM_COMMAND:{
if (LOWORD(wParam) == Calculate) {
int A = 0;
TCHAR textread[256];
*((LPWORD)&textread) = 256; // <-- add this
SendMessage(Box1, EM_GETLINE, 0, (LPARAM)textread);
_stscanf(textread, _T("%d"), &A);
_stprintf(textread, _T("%d"), A);
SendMessage(Box1, WM_SETTEXT, 0, (LPARAM)textread);
}
break;

Answer 2

I think you have several problems there.
First, you didn't show us what Parse1 is. Beware that you must set the size of the buffer in the first word of the buffer. Also, why do you pass 1 as the WPARAM? This is the zero-based index of the line to retrieve from a multiline edit control, but is ignored if the edit is single line.
Also, what is with the first itoa call?
Here is an example that works:
TCHAR textread[256] = {0};
*(reinterpret_cast<WORD*>(&textread)) = 256;
::SendMessage(hwnd, EM_GETLINE, 0, reinterpret_cast<LPARAM>(&textread));
auto n = _ttoi(textread);
_itot_s(n, textread, 256, 10);
::SendMessage(hwnd, WM_SETTEXT, 0, reinterpret_cast<LPARAM>(&textread));