Problem with array pass by condition

Question

Good day. I am trying to write a simple program that will substitute other values from the source text. The problem is that the program replaces the values of only the first five elements and, if they are written together without punctuation marks, adding Latin letters, for example, generally crashes the program. I tried to increase the value of the variable that is responsible for replacing the elements, but the problem is solved 50 to 50. It is painted the same way. Only a string of fused letters is greater. Source code below. Just lay out the whole project. Maybe it will be easier. https://yadi.sk/d/nGIOLDqB35vc7y

#include <Windows.h> #include"resource.h" HWND hEdit1; HWND hEdit2; const int m = 1000, n = 5; CHAR str[m] = { 0 }; CHAR rezult[] = { 0 }; CHAR buttons[n] = { 'X','Y','A','B' }; BOOL CALLBACK DlgProc(HWND hwnd, UINT uMsg, WPARAM wParam, LPARAM lParam); int CALLBACK WinMain(HINSTANCE hInstance, HINSTANCE hPrevInst, LPSTR lpCmdLine, int nCmdShow) { DialogBoxParam(hInstance, MAKEINTRESOURCE(IDD_DIALOG1), 0, (DlgProc), 0); return 0; } BOOL CALLBACK DlgProc(HWND hwnd, UINT uMsg, WPARAM wParam, LPARAM lParam) { switch (uMsg) { case WM_INITDIALOG: { hEdit1 = GetDlgItem(hwnd, IDC_EDIT1); SetWindowText(hEdit1, str); SetFocus(hEdit1); hEdit2 = GetDlgItem(hwnd,IDC_EDIT2); SetWindowText(hEdit2, rezult); break; } case WM_COMMAND: switch (LOWORD(wParam)) { case IDC_BUTTON1: GetWindowText(hEdit1, str, 255); for (int i = 0; i<n; ++i) if (str[i] > '0' && str[i] < m + '0') { str[i] = buttons[str[i] - '0' - 1]; } SetWindowText(hEdit2, str); break; case IDOK: MessageBox(hwnd, "OK", "Info", MB_OK || MB_ICONINFORMATION); break; case IDCANCEL: EndDialog(hwnd, 0); return FALSE; } break; case WM_CLOSE: EndDialog(hwnd, 0); return FALSE; } return FALSE; }

As far as I know an array like with 0 starts counting. And I need 1 = X, 2 = Y, 3 = A, 4 = B. - Petr

user194374 · Accepted Answer · 2016-12-30T11:18:28

This cycle

  for (int i = 0; i<n; ++i) if (str[i] > '0' && str[i] < m + '0') { str[i] = buttons[str[i] - '0' - 1]; }

makes no sense. Since the variable m has a value of 1000

 const int m = 1000, n = 5; ^^^^^^^^

then, in fact, this condition

 if (str[i] > '0' && str[i] < m + '0')

will be executed for any str[i] value greater than '0' . However, the correct range of indices for the array of buttons , declared as

 CHAR buttons[n] = { 'X','Y','A','B' };

this is just [0, 3] . Thus, for any value of str[i] that is greater than '4' going beyond the array will occur, which leads to unspecified program behavior.

It turns out you need to remove the limit on the array itself?
@Petr First, you have a loop from 0 to 4 for (int i = 0; i <n; ++ i), so only 5 initial characters of the string are checked.
And, secondly, you need to ensure that the index in the buttons array does not go beyond it.
I applied the exact same array in the program in the console view and everything worked fine there.
@Petr Keep in mind that you may have UNICODE enabled, and therefore you must deal with "wide" characters.

Problem with array pass by condition

1 answer 1

More articles: