The best way to execute a sequence once in C++ - c++

Question

Using C++ What could possibly the best way for a sequence to run only once? To make it clearer for example that I have a program in where you need to guess a string, if the user entered hint I would display the hint of the word but I would only allow it once... I am currently doing this:
bool hintLock = false;
...
if (guess == "hint"){
if (!hintLock){
cout << hint << endl;
hintLock = true;
}
else
cout << "I've given you the hint" << endl;
}
Here's my code:
#include <iostream>
#include <string>
using namespace std;
void main(){
string guess;
bool hintLock = false;
cout << "Guess one of StackExchange's best site: Type \"hint\" for hint" << endl << endl;
do{
cout << "Guess > ";
cin >> guess;
if (guess == "hint"){ // Here it is
if (!hintLock){
cout << hint << endl;
hintLock = true;
}
else
cout << "I've given you the hint" << endl;
}
}
while (guess != "stackoverflow");
cout << "You've got it right!" << endl;
}
Is there any much better statement to do this? or is it already the best?

Answer 1

I suspect that either you are overanalyzing things or you haven't adequately described the real problem. From the code you've posted, I see no reason why you shouldn't wrap the code you want to execute in to a function and then simply call that function one time.
void blahBlah()
{
// blah blah
}
int main()
{
if (userInput == "hint")
blahBlah();
}
Perhaps what you meant is that in your program you have a main loop which executes until program termination, and in that loop you accept input from the user. The user is allowed to ask for a hint, but only once during the program's run. The first time the ask for a hint they are given one, but subsequent times they are not.
I still believe simple is better than fancy (read: complex). To that end, I start with having a bool scoped outside of the main loop which you check each time they ask for help:
int main()
{
bool displayedHint = false;
// program's main loop
for (bool endProgram = false; !endProgram; )
{
std::string command = getUserInput();
if (command == "hint")
{
if (displayedHint)
{
cout << "I already gave you a hint!\n";
}
else
{
displayHint();
displayedHint = true;
}
}
}
}

Answer 2

If you want to make sure it only shows once for any particular run of the program (anything more global than that is pretty complicated and platfrom-specific), all you need is a global boolean to protect the function. For example:
bool shownHint = false;
void showHint() {
if (!shownHint) {
cout << "The hint is: ........" << endl;
shownHint = true;
} else {
cout << "Hint has already been shown, no cheating!" << endl;
}
Whenever you think you might want to show the hint, call showHint() and it will show (or not) as appropriate.
The trick is making sure the variable is global (or a static, in a class, which looks almost the same), so that it doesn't get reset during your loop or otherwise while the program is running.
If you need to persist between runs, you could write to a file, check a server, set a registry key, or any number of other options.

Answer 3

I think that the most appropriate iteration statement is do-while. It allows at least one iteration
for example
do
{
std::cout << "Enter your word: ";
std::string answer;
std::cin >> answer;
// some other stuff
} while ( false );
Or
bool allow = true;
do
{
std::cout << "Enter your word: ";
std::string answer;
std::cin >> answer;
// some other stuff
} while ( allow = !allow );

Answer 4

You can use flags that are boolean, that represent a state in your system. Once the state is "defined", you can then query the state and find if it is "set" or "cleared"..
to be more precise
bool hasHinted = false; // unset or cleared( also definition of a state variable)
if(hasHinted == false){
//do something
hasHinted = true; // set
}else{
// do nothing
}

Answer 5

I think the OP is looking for a piece of code similar to singleton init. i.e.: only create the singleton once, and after that always return the pointer.
void Init() {
static bool isInitialized = false;
if (!isInitialized) {
isInitialized = true;
doRealInit();
}
}
the same thing done with std::call_once as a comment suggests:
std::once_flag flag;
void do_once() {
std::call_once(flag, [](){ std::cout << "Called once" << std::endl; });
}
in my opinion it's not really more readable or shorter.