I am using ubuntu. I have written a program to calculate prime factors. it works perfectly fine till entered number is less than 9989 (or so ) but when one enters a number higher than that, for example 15000, it does not work. Can anyone guide me whats the problem ? although new codes are welcome, but i want to know problem with my code. thanks in Advance
Code:
#include<stdio.h>
void prime_factors( int );
int next_prime_no( int );
int main()
{
int num;
printf("Enter a number : ");
scanf("%d",&num);
prime_factors(num);
return 0;
}
void prime_factors( int a)
{
int r,p,c=a;
for(p=2;p<=c;p=next_prime_no(p)) //checking for prime factors starting from 2 and then finding next higher prime number
{
while(a>0)
{
if(p==c) //printing the number itself if no prime factors other than itself.
{
printf(" Factors of %d are 1 and %d \n\n",c,c);
a=0;
break;
}
else
{
r=a%p;
if(r==0)
{
printf(" %d ",p);
a=a/p;
}
else
{
break;
}
}
}
}
printf("\n\n\n");
}
int next_prime_no(int p) // finding the next higher prime number
{
int i,r,j;
for(i=p+1;i<10000;i++)
{
r=0;
for(j=2;j<i;j++)
{
r=i%j;
if(r==0)
break;
}
if(r!=0)
{
return i;
break;
}
}
}
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LEARN ABOUT CENTOS
bn_generate_prime
BN_generate_prime(3) OpenSSL BN_generate_prime(3)NAME
BN_generate_prime, BN_is_prime, BN_is_prime_fasttest - generate primes and test for primality
SYNOPSIS
#include <openssl/bn.h>
BIGNUM *BN_generate_prime(BIGNUM *ret, int num, int safe, BIGNUM *add,
BIGNUM *rem, void (*callback)(int, int, void *), void *cb_arg);
int BN_is_prime(const BIGNUM *a, int checks, void (*callback)(int, int,
void *), BN_CTX *ctx, void *cb_arg);
int BN_is_prime_fasttest(const BIGNUM *a, int checks,
void (*callback)(int, int, void *), BN_CTX *ctx, void *cb_arg,
int do_trial_division);
DESCRIPTION
BN_generate_prime() generates a pseudo-random prime number of num bits. If ret is not NULL, it will be used to store the number.
If callback is not NULL, it is called as follows:
o callback(0, i, cb_arg) is called after generating the i-th potential prime number.
o While the number is being tested for primality, callback(1, j, cb_arg) is called as described below.
o When a prime has been found, callback(2, i, cb_arg) is called.
The prime may have to fulfill additional requirements for use in Diffie-Hellman key exchange:
If add is not NULL, the prime will fulfill the condition p % add == rem (p % add == 1 if rem == NULL) in order to suit a given generator.
If safe is true, it will be a safe prime (i.e. a prime p so that (p-1)/2 is also prime).
The PRNG must be seeded prior to calling BN_generate_prime(). The prime number generation has a negligible error probability.
BN_is_prime() and BN_is_prime_fasttest() test if the number a is prime. The following tests are performed until one of them shows that a
is composite; if a passes all these tests, it is considered prime.
BN_is_prime_fasttest(), when called with do_trial_division == 1, first attempts trial division by a number of small primes; if no divisors
are found by this test and callback is not NULL, callback(1, -1, cb_arg) is called. If do_trial_division == 0, this test is skipped.
Both BN_is_prime() and BN_is_prime_fasttest() perform a Miller-Rabin probabilistic primality test with checks iterations. If checks ==
BN_prime_checks, a number of iterations is used that yields a false positive rate of at most 2^-80 for random input.
If callback is not NULL, callback(1, j, cb_arg) is called after the j-th iteration (j = 0, 1, ...). ctx is a pre-allocated BN_CTX (to save
the overhead of allocating and freeing the structure in a loop), or NULL.
RETURN VALUES
BN_generate_prime() returns the prime number on success, NULL otherwise.
BN_is_prime() returns 0 if the number is composite, 1 if it is prime with an error probability of less than 0.25^checks, and -1 on error.
The error codes can be obtained by ERR_get_error(3).
SEE ALSO bn(3), ERR_get_error(3), rand(3)HISTORY
The cb_arg arguments to BN_generate_prime() and to BN_is_prime() were added in SSLeay 0.9.0. The ret argument to BN_generate_prime() was
added in SSLeay 0.9.1. BN_is_prime_fasttest() was added in OpenSSL 0.9.5.
1.0.1e 2013-02-11 BN_generate_prime(3)
08-16-2014
Memory allocation problem
