Ive been working on learning C++ and i cant seem to find a code for using more cpu on a multi core processor?

This program is so slow and it is not using as much CPU time as you expect because you're flushing the output stream on every iteration of the loop, which is what endl does. Many tutorials make the mistake of using it to indicate end of line. Change that to '\n', and compare:

for (int x=0;x<100001;x++)

     cout << x << '\n';

cout << endl; // you need this only once and only before system("pause")

system("pause"); // which is not needed at all, just run the program from a console window

now it should run much faster, but it would still be executing on one CPU. To parallelize, you will have to learn about threads and concurrent programming in general, which is a complicated topic.

The reason the program counts only 2500 per second and uses only 3% of the CPU power is that it is printing the number to the screen on every iteration of the loop. Whenever it prints, the CPU has to stop and wait for the system and the display to catch up. If you took away the line displaying the number in the loop, it would count at a rate of hundreds of millions per second, and would probably complete in less than 1 millisecond (which is too short a time for a human to even notice), but during that 1 millisecond it would suck up all the extra power in a single core. If your system is 1-core, that would be 100% CPU usage. More likely your system is multicore, in which case the usage would only go to some integer fraction of 100% (i.e. 50% on a 2-core system, 25% on a 4-core system, etc), and because the display of CPU usage updates much less frequently than once every millisecond, you probably wouldn't get to see it spike even that high. Increasing the length of the loop to a billion or so would give you a few seconds and you'd probably get to see the full usage.

That said, this still doesn't address the meat of your question, which is, how to you take advantage of more than one core at once? You absolutely can do it, and doing it involves something called 'threading'. Right now, your program runs only a single thread. What you have to do is set it up so that it starts multiple threads. Then the system will automatically pass off active threads to other cores. However, this is not as simple (not NEARLY as simple) as setting 'threads=4' or something and then running everything else normally. Multiple cores don't let you execute a single sequence of instructions faster. What they do is let you execute multiple sequences of instructions simultaneously. This introduces some really crazy problems that you haven't even conceived of so far. For instance, with a singlethreaded program, if I wrote this:

int n=0;

void blah()

{

n=5;

cout<<n<<"\n";

}

and called blah(), I would be guaranteed to get '5' printed to the console. But with a multithreaded program, I don't get that guarantee anymore, because some other thread might come along and change the value of n between the line that sets n to 5 and the line that prints it to the console. Yes, 'between'. Now, if your two threads are never going to interact and everything they do treats separate sets of data, you'll never have that problem. But in the real world, you usually want the threads to interact in some way, and that means you have to start using some new mechanisms (such as locks) to make sure you can modify data safely and avoid breaking the program logic. Furthermore, because of the unpredictable way that schedulers work, you can have situations where an improperly written program will work perfectly 999 times out of 1000, and then fail catastrophically that 1 other time because a thread got scheduled at just precisely the wrong moment. This turns debugging multithreaded code into a colossal unholy nightmare that will make you want to scrape your own eyeballs out of their sockets with a rusty fork (no pun intended). Unfortunately, safe multithreaded programming is something any professional programmer (or even any serious amateur) will have to learn eventually, and it's becoming increasingly important as computers get more and more cores.

You can check out pages such as the following for information on threading:

http://en.wikibooks.org/wiki/C++_Programming/Threa...

http://www.linuxselfhelp.com/HOWTO/C++Programming-...

K. If the computer is busy with other stuff then that might be all that it can spare but, what you want to do is learn about threads and to be honest you don't need to worry about that until later(once you can actually write code).

As far as this program goes, it's not particularly computer intensive and it's not programmed to use threads so it's only going to run on 1 of your 4 cores anyways.

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