pi(e)

[zacariaz]

@code
#include <iostream>
#include <cmath>

int main() {
double cache;
unsigned long n;
for (n = 1; n != 0; n++) {
cache += 1/n;
std::cout << sqrt(cache*6) << std::endl;
}
}
@end

As far as im concerned this should work, but ofcourse it doesnt.
I must have done somthing wrong, but i fail to see where.
To those in doubt, these few line should calculate pi (3.1415.....)

Thanks in advance.

Zacariaz

 

[Kai-Uwe Bux]

@code
#include <iostream>
#include <cmath>

int main() {
double cache;

You should initialize this value:

double cache = 0.0;

unsigned long n;
for (n = 1; n != 0; n++) {
cache += 1/n;

1/n is an unsigned long. Thus, you get cache = 1 after the first iteration.
From there on, 1/n == 0 and cache does not change. Thus, the next line will
always print sqrt(6).

Try

cache += 1.0/n;

std::cout << sqrt(cache*6) << std::endl;
}
}
@end

As far as im concerned this should work, but ofcourse it doesnt.
I must have done somthing wrong, but i fail to see where.
To those in doubt, these few line should calculate pi (3.1415.....)

Oh, wait: in that case

cache += 1.0/n;

would not do you good, either since there is a mistake in the math, too: You
will want

cache += sqr(1.0/n);


Finally, for better precision, you should reverse the order of this loop:
start with a large n and go down to 1.


Best

Kai-Uwe Bux

 

[Duane Hebert]

@code
#include <iostream>
#include <cmath>

int main() {
double cache;

This double is not initialized so it could be anything

unsigned long n;

This should be declared inside of the loop

for (n = 1; n != 0; n++) {
cache += 1/n;

Don't you mean 1.0/n ? 1/n is going to
return a long which will truncate so basically,
the first time it adds 1 and then 0 until the
unsigned long wraps to 0.

std::cout << sqrt(cache*6) << std::endl;
}
}
@end

As far as im concerned this should work, but ofcourse it doesnt.
I must have done somthing wrong, but i fail to see where.
To those in doubt, these few line should calculate pi (3.1415.....)

I don't think so. I would expect it to keep printing the same
number for an incredibly long time if it doesn't crash.
With msvc 2005, the initial value of
cache is -9.2559631349317831e+061.

After an initial break to tell me that cache is being used
without initialization, it goes on to print
1.#IND repeatedly.

 

[zacariaz]

Working now, and have corrected the error so now it estimates pi as it
should, but, i only get 5 digits, what can i do to get more?

@code
#include <iostream>
#include <cmath>

int main() {
double cache = 0.0;
for (unsigned long n = 1; n != 0; n++) {
cache += 1.0/pow(n,2);
std::cout << sqrt(cache*6) << std::endl;
}
}
@end

 

[zacariaz]

This looks a litle better:

@code
#include <iostream>
#include <cmath>

int main() {
double cache = 0.0;
for (unsigned long n = 1000000; n != 0; n--) {
cache += 1.0/pow(n,2);
}
std::cout << sqrt(cache*6) << std::endl;
std::cin.get();
}
@end

 

[osmium]

in message news:[email protected]...

Working now, and have corrected the error so now it estimates pi as it
should, but, i only get 5 digits, what can i do to get more?

There are tons of articles about different methods of computing pi. Look
around the web. Use "algorithm" as one of the search terms.

 

[zacariaz]

osmium skrev:

in message news:[email protected]...

There are tons of articles about different methods of computing pi. Look
around the web. Use "algorithm" as one of the search terms.

I know, i just wanted to see if this actually worked, it just seemed
too simple...

 

[peter koch]

(e-mail address removed) skrev:

osmium skrev:

Check how many decimals you print.

I know, i just wanted to see if this actually worked, it just seemed
too simple...

It is not too simple. It works.

/Peter

 

[zacariaz]

peter koch skrev:

(e-mail address removed) skrev:


Check how many decimals you print.

i print 5 but would like to print a few more just to see how slow this
is...

 

[Marcus Kwok]

i print 5 but would like to print a few more just to see how slow this
is...

If you want to print more decimals, look up std::setprecision() and
std::fixed in <iomanip>.