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C++ Discussion Thread
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May 4th, 2007

small question

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Could you tell me the mean of this code?

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

thanks!

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donaldunca

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May 4th, 2007

Re: small question

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,

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.

Bench

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May 4th, 2007

Re: small question

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:

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:

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.

yesm

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May 5th, 2007

Re: small question

Click to Expand / Collapse Quote 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:
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.

WaltP

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May 5th, 2007

Re: small question

thank you for your helps

donaldunca

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