How concatenate a char with TCHAR array?

I want concatenate a random string with a directory name and the final result must be something like this:

C:\Program Files (x86)\AAAFFF1334

On following code this part: "AAAFFF1334" comes strange characters see:

What must be made to fix this?

TCHAR mydir[MAX_PATH];

void gen_random(char *s, const int len) {
    static const char alphanum[] =
        "0123456789"
        "ABCDEFGHIJKLMNOPQRSTUVWXYZ"
        "abcdefghijklmnopqrstuvwxyz";

    for (int i = 0; i < len; ++i) {
        s[i] = alphanum[rand() % (sizeof(alphanum)-1)];
    }

    s[len] = 0;
}

// main

TCHAR szProgramFiles[MAX_PATH];
HRESULT hProgramFiles = SHGetFolderPath(NULL, CSIDL_PROGRAM_FILES, NULL, SHGFP_TYPE_CURRENT, szProgramFiles);

char str;

gen_random(&str, 10);

wsprintf(mydir, TEXT("%s\\%s"), szProgramFiles, str);

gen_random should get char array with at least 11 characters (10 for size + 1 for terminating null).

So it should be:

char str[10+1]; //or char str[11];
gen_random(str, 10);

in addition, the format string should be: "%s\\%hs", the first is TCHAR* type (if UNICODE defined wchar_t* if not char*) the second is always char* type.

hs, hS

String. This value is always interpreted as type LPSTR, even when the calling application defines Unicode.

look here

Note: in Microsoft documentation:

• LPSTR = always char*
• LPWSTR = always wchar_t*
• LPTSTR = TCHAR* (if UNICODE defined: wchar_t*, else: char*)