C++ While Loop help

[Swenghk]

I was working on a text-based game and I want the program to continue prompting the user until he/she enters a valid answer...Here is what i have, but it won't work...what's wrong with it?


while (true)
{
cout << "\n\nChoose: ";
cin >> menuChoose;

if (menuChoose == 1)
{
newGame();
break;
}

if (menuChoose == 2)
credits();

if (menuChoose == 3)
quitGame();

else
{
cout << "\nYour choice was invalid!";
}

[credobyte]

else {
cout << "Wrong answer! \n";
continue; // should start the while loop over and over again until satisfied ( if )
}

Still learning tough :P

[WRDN]

If it won't compile, its because you haven't closed the while loop.

Change it to this and it will work:



while (true)
{
cout << "\n\nChoose: ";
cin >> menuChoose;

if (menuChoose == 1)
{
newGame();
break;
}

if (menuChoose == 2)
credits();

if (menuChoose == 3)
quitGame();

else
{
cout << "\nYour choice was invalid!";
}
}

[Martin Witte]

You have to make sure menuChoose is evaluated only once per loop

#include <iostream>

using std::cout;
using std::cin;
using std::endl;

void newGame() { cout << "new game" << endl; }
void credits() { cout << "credits" << endl; }
void quitGame() { cout << "quit" << endl; }

int main()
{
int menuChoose(0);

while (true)
{
cout << endl << endl << "Choose: ";
cin >> menuChoose;
if (menuChoose == 1)
{
newGame();
break;
}
else if (menuChoose == 2)
{
credits();
}
else if (menuChoose == 3)
{
quitGame();
break;
}
else
{
cout << "Your choice was invalid!" << endl;
}
}

return 0;
}

A kind request: please always post a minimal example which compiles and shows your problem (or if you have a cryptic compiler error which shows the error)

[Swenghk]

I tried continue, but it gives me this


Choose:
Your choice was invalid!

Choose:
Your choice was invalid!

Choose:
Your choice was invalid!

Choose:
Your choice was invalid!

Choose:
Your choice was invalid!



It gets stuck in an infinite loop...

[.Maleficus.]

You will always be stuck in an infinite loop with the code you have (and were given). This should be the indicator:

while (true)
If it never evaluates to false, why would it stop?

[c0mput3r_n3rD]

you can also just do this: (which i find easier)

while(menuChoose != 1 || menuChoose != 2 || menuChoose != 3)
{
cout << "wrong choose\n";
cout << "Re-enter: ";
cin >> menuChoose;
}
/* then do a if(menuChoose == 1) { /*do w/e */ }
else if(menuChoose == 2) { /*do w/e*/ }
else /*do w/e*/

--That's just me though

[dwhitney67]

I believe the example provided earlier are fine, but only for certain cases.

I bet the OP is trying to input values other than integers, and that is what is throwing his application for a spin.

So borrowing Martin Witte's example, and tweaking it a bit, I came up with this working example:


include <iostream>

using std::cout;
using std::cin;
using std::endl;

void newGame() { cout << "new game" << endl; }
void credits() { cout << "credits" << endl; }

int main()
{
unsigned int menuChoose(0);
bool quit = false;

while (!quit)
{
cout << "1. New Game.\n"
<< "2. Credits.\n"
<< "3. Quit.\n\n"
<< "Choose: ";

cin >> menuChoose;

if (!cin.good() || menuChoose < 1 || menuChoose > 3)
{
cout << "Your choice was invalid!" << endl;
cin.clear();
cin.ignore(1024, '\n');
continue;
}

switch (menuChoose)
{
case 1: newGame(); break;
case 2: credits(); break;
case 3: quit = true; break;
}
}

return 0;
}

Note that the issue was resolved with the usage of cin's clear() and ignore() methods. The rest was merely reorganization of the code.

[Swenghk]

You will always be stuck in an infinite loop with the code you have (and were given). This should be the indicator:

while (true)
If it never evaluates to false, why would it stop?

You provide an exit...like break, a function call, or continue

[unknownPoster]

you can also just do this: (which i find easier)

while(menuChoose != 1 || menuChoose != 2 || menuChoose != 3)
{
cout << "wrong choose\n";
cout << "Re-enter: ";
cin >> menuChoose;
}
/* then do a if(menuChoose == 1) { /*do w/e */ }
else if(menuChoose == 2) { /*do w/e*/ }
else /*do w/e*/

--That's just me though

Except for the fact that your proposed solution won't work. You made a simple flaw in boolean logic...




while(menuChoose != 1 && menuChoose != 2 && menuChoose != 3)
{
cout << "wrong choose\n";
cout << "Re-enter: ";
cin >> menuChoose;
}



The above is a more appropriate solution...

[dwhitney67]

...

while(menuChoose != 1 && menuChoose != 2 && menuChoose != 3)
{
cout << "wrong choose\n";
cout << "Re-enter: ";
cin >> menuChoose;
}

[/code]

The above is a more appropriate solution...

Yes, but it does not address the issue the OP was having. Please take a look at my previous post where I provided a working solution, although not a very good one.

[Swenghk]

I don't know what it is...maybe it's my compiler or something, but I trieds everything above. But when i run it, it just displays the message indicating the user entered something wrong endlessly...is there any other way to do this?

[Swenghk]

Wait! Nevermind!

dwhitney67's example worked...I just don't understand some of the member functions you're using...what book contains those?

[dwhitney67]

Wait! Nevermind!

dwhitney67's example worked...I just don't understand some of the member functions you're using...what book contains those?

Go here: http://www.cplusplus.com/reference/

Look under the section for IOstream Library, or more specifically for istream (click the appropriate box in the diagram).

[Swenghk]

Thank you everybody for all of your help!

[Can+~]

you can also just do this: (which i find easier)

while(menuChoose != 1 || menuChoose != 2 || menuChoose != 3)
{
cout << "wrong choose\n";
cout << "Re-enter: ";
cin >> menuChoose;
}
/* then do a if(menuChoose == 1) { /*do w/e */ }
else if(menuChoose == 2) { /*do w/e*/ }
else /*do w/e*/

--That's just me though

Remember De Morgan's laws (http://en.wikipedia.org/wiki/De_Morgan%27s_laws)?

x != 1 || x != 2 || x != 3 <=> !(x == 1 && x == 2 && x == 3)

That implies that the value is true when what's inside the parenthesis is false, and it will always be false for any value of x defined on integers, ergo, condition will always be true.

It's a common mistake ;), I had a lot of them when I first started with logic.

As for the OP, there other fun ways to create menus, instead of "switching" or "if-ing" (if that's a word), you can also create a Hash with pointers to function, which is my personal favorite :KS (Although, it's kinda overkill here, but great thing to learn).