Memory allocation problem Post: 302913411

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Top Forums UNIX for Dummies Questions & Answers Memory allocation problem Post 302913411 by bakunin on Saturday 16th of August 2014 10:11:10 AM

08-16-2014

Registered User

Quote:

Originally Posted by Abhishek_kumar

Can anyone guide me whats the problem ? although new codes are welcome, but i want to know problem with my code

Fair enough. The first problem, without even looking at what your code does, is obvious: use speaking names for your variables. Instead of juggling around "i", "j", "k", "p" and whatnot, like in good old FORTRAN/77, you should write names which tell you instantly what is in them: numbers, primes, factors, whatever. Not only will that help you with housekeeping, it will help you to concentrate on coding instead of remembering what "i" exactly means now in this function.

My personal favorite in this regard (but that is a matter of taste) is "Hungarian Style Notation" - or at least some personal subset variation of it. I prefix my variables names with a type indicator, which helps remembering this vital fact.

Secondly, regarding your code: the problem you are experiencing is IMHO in the function next_prime(), in this line:

Code:

	for(i=p+1;i<10000;i++)

Actually the program does what you told it to do and therefore this loop is interrupted at 9999 (not "9989 (or so )", as you said).

Aside from that your code inefficient to the extreme. Because "2" is a prime you could skip all even numbers and increment i by 2 instead of one, yes? This, btw., could be done with all the other found primes too. This consideration is the basis of the "Sieve of Eratosthenes", which will work for very small numbers like the ones you deal with. For bigger numbers you need better algorithms, like Lucas-Lehmer, Adleman-Pomerance-Rumely, etc..

For a quick introduction to primality tests and their pros and cons start with searching for "Primality Test" in Wikipedia.

I hope this helps.

bakunin

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