[OrMisicL]

pawn Код:

stock IsLetter(c)
{
    return ((c >= 65 && c <= 91) || (c >= 97 && c <= 123)) ? true : false;
}

// Under on OnDialogResponse
new bool:valid = false;
for(new i = 0; i < strlen(inputtext); i++)
{
    if(IsLetter(inputtext[i]))
    {
        valid = true;
        break;
    }
}
if(valid)
{ 
    // Success code
}
else
{
    SendClientMessage(playerid, COLOR, "Your password must contain at least one character");
}