Thread: Help me with my basic program, nothing I create will run

Originally Posted by MacGyver

Find a simple algorithm for finding prime numbers. Don't overcomplicate it.



Well, what should the compiler assume?

Code:

int main(void)
{
	int y;
	y = 5; /* there is only 1 y, so the compiler knows which one to use. */

	return 0;
}

Note the giant braces. When you say, y = 5, it looks for y inside the current braces. If there was a global variable also named y, then the compiler would still use the one inside main(). It assumes that you mean the most inner-declared variable.

It won't look inside other functions, though, for a variable. A valid variable is either inside the current set of braces, inside the current function, or declared globally. That's about it.

Ok I can grasp that (=
I'm thinking searching for an existing algorithm for finding prime numbers would be cheating myself but if thats all theres left to do... (=

Thanks again,
-Ravens'Wrath

Of course, there are many examples of algorithms that find prime numbers. If you don't know how to search for prime numbers with a pencil and paper (and maybe a calculator), then you will need to use somebody else's algorithm.

You can't expect to program a computer to do something that you don't know how to do, yourself.

If you do know how to search for prime numbers by hand, then programming a computer to do it is an excellent challenge, and you'll learn a lot, as well.

I won't let you fail, so don't worry.

If you want to work with me on this, let me know, and we'll move along, smartly. There's been several good posts here, but they've been geared to a more C refinement to your code, rather than a C "let's solve this problem, learn a bit, and have some fun" kind of approach.

If you want to go with this, just jot down the steps you use to find a prime, by hand, in either plain English or pseudo code. We'll flush it out from there.

Adak

Been a way for one day and so many posts (=
Thanks for your time in trying to help. And to answer everyones question, yes I know what a prime number is :P Im just having trouble setting up a program that will find them...

I have made another attempt to try do this but I have had the same problem as before, I can get a program to compile but thats about it, the following is how I'm attempting to solve the problem:

Code:

/* program to find first 100 prime numbers */

#include <stdio.h>
int main(void)
{

int counter, test_n, divisor;
counter = 100;
test_n = divisor = 2;

while (counter) 

{

	if (test_n == divisor)
		{
 		printf("%d is prime", test_n);
  		counter = counter - 1;
		test_n = test_n + 1;
		divisor = 2;
	 	}
	else
		while (test_n % divisor)
			{
			divisor = divisor +1;
			}
	if (test_n != divisor)
		{
		divisor = 2;
		test_n = test_n + 1;
		}
}


return 0;
}

My program seems to be nearly right... But still doesn't give me all of the first 100 primes (although it does seem to list only primes, haven't checked all though).

Any ideas why this isn't working...
by the way, my trash has 76 copies of a.out and they're all attempts at this silly program...

so any help would be greatly appreciated.