C - Mathematics - Find prime numbers

If you have a good computer, you can maybe try to find the last prime number that nobody found yet.

Indeed, you can even win a prize for that!
But you have to find a number with more than millions of digits.

I'm sure you can do it.

For the moment, let's see how to find these numbers in this prime number tutorial.

Arguments are a range: the minimum and the maximum numbers.

For example, I passed 2 as first argument and 100 as second argument, so the result displays all prime numbers between 2 and 100.
Notice that this example works until the max value of an unsigned int: 4,294,967,295.

You are of course free to modify the example to reach a greater value.

Find prime numbers

main.c

/* main.c */

#include "h.h"

int     main(int ac, char *av[])
{
    t_bp b;

    init(ac, av, &b);
    debug(&b);
    return 0;
}

misc.c

/* misc.c  */

#include <stdlib.h>
#include <stdio.h>
#include <errno.h>
#include <string.h>

#include "h.h"

void init(int ac, char *av[], t_bp *b)
{

    if (ac < 3)
    {
        printf("Usage: ./prime-number [min] [max]\n");
        exit(1);
    }
    if (atoi(av[1]) <= 1 || atoi(av[2]) <= 1)
    {
        fprintf(stderr, "Error: %s\n", "Arguments must be greater than 1");
        exit(1);
    }
    b->numberMin = atoi(av[1]);
    b->numberMax = atoi(av[2]);
    if ((b->numberMin > b->numberMax) || (b->numberMin == b->numberMax))
    {
        fprintf(stderr, "Error: %s\n", "Min must be less than Max.");
        exit(1);
    }
}

void debug(t_bp *b)
{
    printf("\n===== START =====\n\n");
    prime_testing(b);
    printf("\n===== END =====\n\n");
}

void prime_testing(t_bp *b)
{
    unsigned int i, j, k;
    int pn;

    i = b->numberMin;
    j = 0;
    while (i <= b->numberMax)
    {
        j = i;
        k = 2;
        pn = 1;
        while (k < j)
        {
            if (j % k == 0)
            {
                pn = 0;
            }
            ++k;
        }
        if (pn > 0)
        {
            printf("%d\n", j);
        }
        ++i;
    }
}

h.h

#ifndef H_H_
#define H_H_

/**
 * Structure
 */
typedef struct primes
{
    unsigned int numberMax;
    unsigned int numberMin;
} t_bp;


/**
 * Prototype
 */
void init(int ac, char *av[], t_bp *b);
void debug(t_bp *b);
void prime_testing(t_bp *b);

#endif /* H_H_ */

Compiling

$ gcc main.c misc.c -o prime-numbers ; ./prime-numbers 2 100

Result

===== START =====

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

===== END =====

Good job! wink

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