Need Help creating a prime number function!

[jewleeuhn]

Hello fellow programmers,

I'm a bit new to programming, and I am trying to create a function that reports prime numbers between a number k and a number secondnum. Here's where I am so far:

void prime_number(int k, int secondnum)
{
    int i;
    int m;
    int j = secondnum;
    for (i = k; i<=j; i++)
    {
        m = i;
        m = m%2;
        if(m!=0)
        {
            printf("%d is a prime number.\n", i);
            continue;
        }
    }
}

When I call the function, when k = 1 and secondnum = 5, it prints out:

1 is a prime number.
3 is a prime number.
5 is a prime number.
3 is a prime number.
5 is a prime number.
3 is a prime number.
5 is a prime number.
5 is a prime number.
5 is a prime number.

I'm not sure why it prints out the same number multiple times. Any help is appreciated!

[CommonTater]

Remove line 13 and try it again.

[tbolton]

Hello fellow programmers,

I'm a bit new to programming, and I am trying to create a function that reports prime numbers between a number k and a number secondnum. Here's where I am so far:

void prime_number(int k, int secondnum)
{
    int i;
    int m;
    int j = secondnum;
    for (i = k; i<=j; i++)
    {
        m = i;
        m = m%2;
        if(m!=0)
        {
            printf("%d is a prime number.\n", i);
            continue;
        }
    }
}

When I call the function, when k = 1 and secondnum = 5, it prints out:

1 is a prime number.
3 is a prime number.
5 is a prime number.
3 is a prime number.
....

I'm not sure why it prints out the same number multiple times. Any help is appreciated!

Hi. A couple of things..

I rewrote the program so that it would function as you were expecting it to work. Here's what I ended up with:

#include <stdio.h>

void prime_number(int k, int secondnum);

int main(void) {

    prime_number(1,11);

}

void prime_number(int k, int secondnum) {
    int m;
    
    while( k <= secondnum) {
        m = k;
        m %=2;
        if(m != 0) {
            printf("%d is a prime number.\n", k);
        }
        k++;
    }
}

I'm sure it's not the cleanest code. But, it'll do.

So, a few things. I think a "while" statement here will suit you better. It'll help you reduce unnecessary variables.

Another thing, I removed the "continue" from the if statement.

And finally, this isn't testing if a number is prime, it's testing if it's odd.

Prime numbers are only divisible by 1 and themselves. So, when you hit numbers like 9, 15, 21, etc., you'll start getting "false positives".

Although I do like the "first number, second number" bit. Once you get your formula worked out, you can find all of the prime numbers within a range of two different ones. Never though about doing it that way.

Also, if you're working with Primes, you may want to look into Goldbach's Conjecture.

[subhash.rao]

You need 2 loops
1)to traverse from firstnum to secondnum
2)to traverse from 2 to currentnum and check if it is divisible(remainder is 0)[This is how you find if the number is prime or not]