The Sieve of Eratosthenes - Find primes in Python, Golang, and C

prime-numbers-1.py

#!/usr/bin/env python3
import os, string

max = 1000000

# seed list with first two primes
primes = [2,3]

# set number
start_num = 4

# range of numbers searching for primes
for num in range(start_num, max):
    #intialize not-a-prime as false
    nap = 0

    # cycle through list of known primes
    for prime in primes:
        # check if a previous prime divides evenly
        # into the current number -- if so the number
        # we are checking (num) is not a prime
        if (num % prime) == 0:
            nap = 1
            break
        # if prime squared is bigger than the number
        # than we don't need to check any more
        if prime*prime > num:
           break

    # did we determine it's not a prime
    # if not, then we found a prime
    if nap != 1:
        # add prime to list of known primes
        primes.append(num)
        print(num)

prime-numbers-2.go

package main

import "fmt"

func main() {

	max := 1000000

	primes := []int{2, 3}

	start_num := 4

	// loop through numbers to max
	for num := start_num; num <= max; num++ {
		nap := false

		// check if a previous prime divides evenly
		// into the current number -- if so the number
		// we are checking (num) is not a prime
		for _, prime := range primes {
			if (num % prime) == 0 {
				nap = true
				break
			}

			// if prime squared is bigger than the number
			// than we don't need to check any more
			if prime*prime > num {
				break
			}
		}

		// did we determine it's not a prime
		// if not, then we found a prime
		if !nap {
			primes = append(primes, num)
			fmt.Println(num)
		}
	}

}

prime-numbers-3.c

/*
    Prime Number Finder
    Marcus Kazmierczak, [email protected]
    Created On: March 18, 2002

    # findthem.c  $Revision: 1.3 $
    # Last Updated: $Date: 2002/03/19 06:59:11 $
*/
#include <stdlib.h>
#include <stdio.h>

/*== start/stop range ==*/
#define START 5  // MUST BE ODD
#define STOP 99999999

int main(void)
{
    int nap;
    long num, c, i;
    long *prime;
    
    prime = malloc((STOP/3) * sizeof(long));
    if (!prime) { printf("Memory Allocation Error."); exit(1); }
    
    prime[0] = 2; prime[1] = 3;
    c = 2; /*== initial primes ==*/
    
    /*== only have to check odd numbers ==*/
    for (num=START; num < STOP; num = num + 2)
    {
        nap = 0;  // set not-a-prime false
        
        /*= cycle through list of known primes =*/
        for (i=0; i < c; i++)
        { 
            /*= check if a previous prime divides evenly =*/
            /*= if so the number is not a prime =*/
            if ((num % prime[i]) == 0) { nap = 1; break; }
            
            /*= stop if prime squared is bigger than the number =*/
            if ((prime[i] * prime[i]) > num) { break; }
        }
        
        /*= if not-a-prime, then we found a prime =*/
        if (nap != 1)
        {
            /*= add prime to list of known primes =*/
            prime[c] = num; c++;
            printf("%d \n",num);
        }
    }
    
    free(prime);
}