hi. new here. Im a freshman at UCSB and im taking my first c++ class. I got this assignment in class and i was hoping for some tips.

The value of pi to 15 decimal places is PI = 3.141592653589793 . . . Your job is to write a
program that can be used to find decent approximations to PI. More specifically, your program must find
integers N and D such that the fraction N/D is the best possible approximation to PI and such that D <

I have already set up nested while loops to chug through the fractions and limited the numerator to n <= 3145926. I also set a if condition right in between the while to reduce the numer of times it goest through the calculations by narrowing the numbers between 3 and 4( like pi). such that if( 3*d < n && 4*d > n){

Now the thing works but it takes about 6 hrs to run and for this project the instructor wants us to make one that runs in 2 min or less. I was wondering if anyone has any tips that may help.
thank you

12 Years
Discussion Span
Last Post by Rashakil Fol

If you post code (using code tags) someone may be willing to take a stab at helping you. Without posting code it's like asking "how can I reduce the time it takes me to file out my tax return?".


Well, try all numbers from D to 1,000,000. I was able to write a program that calculates this in under 20 seconds.

BestPi: 3.141592653588651 3126535/995207

I used one loop that went from D equals 1 to 1,000,000, the interior loop is where it gets tricky. Like you said, the ratio of N/D has to be between 3 and 4...

3 < N/D < 4
3*D < N < 4*D

That's all you get without posting your code.



Now the thing works but it takes about 6 hrs to run

LMAO :lol: :lol: :lol: Sorry for laughing so much! But the last time I heard something like that was way back in 1987 on an old Unix computer -- the program (no, I didn't write it) took 48 hours to run. I rewrite it in C and got it to run in under 10 minutes.

Post your program and I'm certain someone will help you with it.


this is what i got now. it still takes a long time. like an hour

int n, d=1, n2, d2;
double pie= 3.141592643563118, guess, piguess = 3.15;

int main()

while(d <= 1000000) {     /* d goes to 1000000 */
n=3.1*d;               /* started n at 3.1 * to get right to pi area*/
while(n <= 3.2*d ){    /*shortened loop for values */

guess = fabs(((double)n/d) - pie); /*abs value to compare guess*/
if( guess < piguess ){
n2= n;
d2= d;
piguess= guess;


printf( "%d / %d", n2, d2);

Edited by happygeek: fixed formatting


Algorithm efficiency is dependant upon eliminating fluff. For example, eliminate reducable fractions. (You've already tested it before... 1/3 ======= 2/6)


A method based on continued fractions will get you the answer in less than a millisecond.

(Ooh I'm being so unhelpful :twisted: )

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