Infinite feedback from a loop?

[ribenaman]

Hi there, this is a problem I've been having for a while, but it was never particularly troublesome until now.
I was wondering if there's a way to stop the infinite feedback from a while loop without using a break

For example,

#include <iostream>
#include <string>

int main()
{
	std::cout << "pick a number\n";
	std::string number;
	std::cin >> number;

	while(true)
	if (number == "1")
	{
		std::cout << "your class is 1\n";
		break;
	}
	else if (number == "2")
	{
		std::cout << "your class is 2\n";
		break;
	}
	else
	{
		std::cout << "sorry, try again\n";
	}
	
	std::cout << "thanks for playing\n";
	system("pause");
}

If you give this a quick run and type in a 3, you'll get a continuous string of spam from the else output.
What I'm wondering is if there's a way to go back to the start of the loop?

Thanks in advance

[Gaminic]

You are going back to the start of the loop, but the value of "number" never changes, because it is set before the loop. Put while(true) before std::cout << "pick a number\n";.

Also, a while should be followed by brackets ({ }) to make sure the entire loop body is executed. Now, only the first statement is evaluated as the loop [but if-else is treated as 'one statement', so you won't notice a difference with the current code. It will mess up your code if you move the while(true) to the start of the main).

Secondly, system() is bad practice: http://www.cplusplus.com/articles/j3wTURfi/
Thirdly, your main should end with return 0;.

[ribenaman]

Thanks very much for the help. I have a couple of questions though. Firstly, what does return 0 do?
Second, that thread was very useful, thank you for that. However it didn't really explain what to use instead. I'm used to using system() or simply setting break points. I was taught another way but I'm afraid I'm drawing a blank

Again, thanks for the help, especially in such a quick response!

[Gaminic]

return 0; tells the calling environment that the program exited successfully. For your current projects it probably makes no difference, and I even think modern compilers assume the return 0 by default anyway, but it's still considered good practice.

To avoid system("pause"), you can use a variety of tricks, going from easy to very complicated. Personally, I use breakpoints or a simple piece of code:

std::cout << "Enter any number to quit.\n";
std::cin >> t; // Random variable from the code somewhere.
return 0;

Code-wise, I think that's as easy as it gets. I simply overwrite the value of a random variable (here: 't'). The program is about to end anyway, so I'm not doing any damage.

[nickoolsayz]

The reason your code is in an infinite loop is your while statement. While true ... then you have nested if statements. while true means loop, and if 3 cout ......, so you will infinitely cout the statement because its true.

i would remove the while. You have to ask yourself what you want your program to do exactly. Then figure whats the best way to create that.

[ribenaman]

Thanks again for all the help, Gaminic.

Nickoolsayz, the loop is not infinite as it is broken if number = 1 or 2, however I need it to be a possibly infinite loop in case the player keeps entering a number that is not 1 or 2.

[nickoolsayz]

not sure exactly what your trying to but but if you are wanted to go back to start the program again maybe you are looking for:

#include <iostream>
#include <string>

int main()
{

do{
	std::cout << "pick a number\n";
	std::string number;
	std::cin >> number;
        //use -1 as a sentinal value to stop the loop.
	while(true)
	if (number == "1")
	{
		std::cout << "your class is 1\n";
		break;
	}
	else if (number == "2")
	{
		std::cout << "your class is 2\n";
		break;
	}
	
        else if (number == -1)
        {
                 std::cout << "thanks for playing\n";
        }
        else
	{
		std::cout << "sorry, try again\n";
	}
}while (number != -1)
	system("pause");
}

this code will not work since im not sure exactly what your looking to do, but its a basic idea of who to use do while for your block of code.