Prime factors code in C and Python

amrlima — Thu, 14 Jan 2010 23:07:11 +0000

Today someone spoke about prime factors and I thought it was something interesting to code. I needed to practice my C so I’ve coded it in C. Here it goes:

#include 
#define VMAX 25
 
int main()
{
    /*Prime numbers < 100 */
    int primes[VMAX] = {2,3,5,7,11,13,17,19,23,29,31,37,41,43,47,53,59,61,67,71,73,79,83,89,97};
    int factors[VMAX] = {}; /*Prime factors*/
    int repeat[VMAX] = {}; /*Store times each factor repeats*/
    int a, i, n=0;
 
    printf("Type a number to find it's prime factors: \n");
    scanf("%d", &a);
 
    /*Start to divide the number by prime numbers while a is not 1*/
    for (i=0; i<VMAX; i++){
        while ((a != 1) && (a % primes[i] == 0)){ 
 
            a = a / primes[i];
            factors[i] = primes[i]; /*The prime factor is the one being used*/
            n++; /*Count how many times each prime is used*/
            } 
        if ((a % primes[i] == 0) ) n = 0; 
        repeat[i] = n;
        n = 0; /*Reinitialize counter*/
 
    }
    printf("Prime factors:\n");
    for (i=0; i<VMAX; i++){
 
        /*Print all factors in the array != 0*/
        if (factors[i] !=0){
            /*Since x ^ 0 = 1, we have to print x ^ 1 instead*/
            if (repeat[i] == 0) printf("%d ^ 1\n", factors[i]);
            else printf("%d ^ %d\n", factors[i], repeat[i]);
        }    
    }       
 
    return 0;
 
}

I really like python but unfortunately I haven’t had the time to code anything with python. Now it’s learning C , then C++ and so on. But this time I wanted to code this in python also. I’m a bit out of practice and my brain was thinking in C. But here it goes.

#! /usr/bin/env/python
VMAX = 25
 
#Prime numbers < 100
primes = [2,3,5,7,11,13,17,19,23,29,31,37,41,43,47,53,59,61,67,71,73,79,83,89,97]
factors = [0]*VMAX #Prime factors
repeat = [0]*VMAX #Store times each factor repeats
i = 0
n = 0
k = 0
 
a = raw_input("Type a number to find it's prime factors:")
 
#Start to divide the number by prime numbers while a is not 1
for i in range(VMAX): 
 
    while ((a != 1) & (int (a) % primes[i] == 0)):
 
        a = int (a) / primes[i]
 
        print primes[i]
        factors[i] = primes[i] # The prime factor is the one being used
 
        n = n + 1 #*Count how many times each prime is used
        print n
    if (int (a) % primes[i] == 0):
        n = 0 #Reinitialize counter
    repeat[k] = n
    n = 0
    k = k + 1
 
print "Prime factors:"
 
#Print all factors in the array != 0
for i in range(VMAX):
 
    if (factors[i] !=0):
    #Since x ^ 0 = 1, we have to print x ^ 1 instead
        if (repeat[i] == 0):
            print factors[i]
        else: print "%s ^ %s " % (factors[i], repeat[i])

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Prime factors code in C and Python