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small question

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Join Date: Sep 2006

Posts: 27

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donaldunca donaldunca is offline

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small question

May 4th, 2007

Could you tell me the mean of this code?

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 C++ Syntax (Toggle Plain Text) 
while(1)
{  // do something
while(1)
{  // do something

thanks!

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Join Date: Feb 2006

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Bench

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Re: small question

May 4th, 2007

Its a way of starting an infinite loop which will be stopped using some means other than the condition inside the brackets next to while.

eg,

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 CPP Syntax (Toggle Plain Text) 
void somefunc()
{
    std::string str;
    while(true)
    {
        std::getline(cin, str);
        if( str == "quit" )
            return;
        else
            std::cout << "You Typed: " << str << std::endl;
    }
}
void somefunc()
{
    std::string str;
    while(true)
    {
        std::getline(cin, str);
        if( str == "quit" )
            return;
        else
            std::cout << "You Typed: " << str << std::endl;
    }
}

IMHO, this kind of idiom is seldom useful - unless you have some compelling reason to do otherwise, you should put an exit condition in the while brackets

Last edited by Bench; May 4th, 2007 at 11:31 am.

¿umop apisdn upside down?

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Join Date: May 2007

Posts: 15

Reputation: yesm is an unknown quantity at this point

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yesm

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Re: small question

May 4th, 2007

Personally, I sometimes use while(1) or similar for things like menus, where choosing a menu option would cause the program to do something and then return to the menu. Then, if you want to exit the program, just return 0 to end the program:

 Help with Code Tags 
 C++ Syntax (Toggle Plain Text) 
int main()
{
   int bob;
   while(1)
   {
      cout << "Enter a number to display, or -1 to exit: ";
      cin >> bob;
      if(bob == -1) { return 0; }
      cout << bob << endl;
    }
}
int main()
{
   int bob;
   while(1)
   {
      cout << "Enter a number to display, or -1 to exit: ";
      cin >> bob;
      if(bob == -1) { return 0; }
      cout << bob << endl;
    }
}

However, some form of exit condition works better, like this:

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 C++ Syntax (Toggle Plain Text) 
int main()
{
    int bob;
   char exit = false;
   while(!exit)
   {
      cout << "Enter a number to display, or -1 to exit: ";
      if(bob == -1) { exit = true; }
      else { cout << bob << endl; }
    }
}
int main()
{
    int bob;
   char exit = false;
   while(!exit)
   {
      cout << "Enter a number to display, or -1 to exit: ";
      if(bob == -1) { exit = true; }
      else { cout << bob << endl; }
    }
}

Of course, your program would probably be a little more complicated.

Edit: Ha, totally didn't see that it had already been answered. My bad!

Last edited by yesm; May 4th, 2007 at 12:24 pm. Reason: Giving credit to previous poster.

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Join Date: May 2006

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WaltP

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Posting Sensei

Re: small question

May 5th, 2007

•

Originally Posted by yesm

Personally, I sometimes use while(1) or similar for things like menus, where choosing a menu option would cause the program to do something and then return to the menu. Then, if you want to exit the program, just return 0 to end the program:
Help with Code Tags

C++ Syntax (Toggle Plain Text)
int main()
{
   int bob;
   while(1)
   {
      cout << "Enter a number to display, or -1 to exit: ";
      cin >> bob;
      if(bob == -1) { return 0; }
      cout << bob << endl;
    }
}
int main() { int bob; while(1) { cout << "Enter a number to display, or -1 to exit: "; cin >> bob; if(bob == -1) { return 0; } cout << bob << endl; } }

This is generally not recommended, although it does work. The reason is you are burying the exit from the function/program in the middle of your code. This could be a maintenance nightmare for the team that inherits your program (or for you in 2 months

) It would be best to break out of the loop and return at the bottom of the function.