I have a problem with a recursive function. The function must return the next prime number.

As parameter I give a number an it must return the number if is prime, or the next prime number. The function works fine in almost cases, when I comment the recursion it shows a list of numbers from one to hundred and allocate the primes. The rest return O. But when I insert the recursive in some cases shows a next prime that is not prime, case of 35 and 95 for example. when I put 4 it show the next prime that is 7. but when it reaches 32 it shows 35 that was not correct. It should shows 37. I don't know were the problem is.

The code is:

#include <stdio.h>
#include <unistd.h>

int     ft_find_next_prime(int nb)
{
    int     i;
    int     z;

    i = nb - 1;
    z = nb;

    while (i > 1)
    {
        if ((z % i) == 0)
        {
             //return (0);
             ft_find_next_prime(  z);
        }
        else
            i--;
    }
    return (z);
}

int     main(void)
{
    int     i;

    i = 1;
    printf("\n\tNUMERO\t---\tSIGIENTE PRIMO\n");
    printf("-----------------------------------------------------\n");
    while (i <= 100)
    {
        printf("\t%i\t---\t%i\n", i, ft_find_next_prime(i));
        i  ;
    }
    return (0);
}

Thanks so much in advance.

CodePudding user response：

The only thing missing in the recursive code is the return keyword, or an assignment of the variable z. The reeason is that the z passed into parameter is a copy, not the original z variable.

int ft_find_next_prime(int nb)
{
    int     i;
    int     z;

    i = nb - 1;
    z = nb;

    while (i > 1)
    {
        if ((z % i) == 0)
        {
            //return (0);
            return ft_find_next_prime(  z);
            // or : z = ft_find_next_prime(  z);
        }
        else
            i--;
    }
    return (z);
}