expected constant expression?

Hello, newbie here.

Just started euler problems to get better acquainted with C. The first problem is this-

If we list all the natural numbers below 10 that are multiples of 3 or 5, we get 3, 5, 6 and 9. The sum of these multiples is 23.


Find the sum of all the multiples of 3 or 5 below 1000.

So here is my program-

Code:

#include <stdio.h>


int main()
{
	int _MAX = 1000;
	int nums[_MAX] = {0};
	int checkers[] = {3,5};
	int k = 0;
	int len = sizeof(checkers)/sizeof(int);
	int sum = 0;
	int checker;


	for(k = 0; k < len; k++)
	{
		checker = checkers[k];
		sum = 0;
		while(sum+checker <= _MAX)
		{
			sum += checker;
			nums[sum] = 1;
		}
	}


	sum = 0;
	for(k = 0; k < _MAX; k++)
	{
		if(nums[k])
			sum += k;
	}


	printf("%d", sum);
	getchar();


	return 0;
}

This compiles with an error-

main.c(6): error C2057: expected constant expression
main.c(6): error C2466: cannot allocate an array of constant size 0

which is line

Code:

int nums[_MAX] = {0};

If I change _MAX here to 1000 everything works and I get the right answer. What is wrong and how do I fix this? I tried google but got more confused.

o_O

Due what it says on the label: make `_MAX' a constant value.

Soma

C Tutor Needed

It means that you're using a C compiler that is not C99 compliant, and from the looks of it, it's some version of MSVC. MSVC is good for C++, but not so good for C.
If you want to MSVC, use an enum or #define for the size.
Otherwise, others will suggest better C compilers such as "Pelles C".

Also, you should not use a leading underscore in your identifiers:
[quote="C99 7.1.3p1]
All identifiers that begin with an underscore and either an uppercase letter or another
underscore are always reserved for any use.
[/code]
It's not likely, but entirely possible, that later on, some implementation you use defines _MAX, and your code no longer works. And pray they don't declare _MAX as a function macro, because it may throw some nasty compiler errors that make no sense when you go back and look at the code.

EDIT: Actually, with a name like _MAX, it's quite likely that an implementation will define it, to be used in calculating the greater of two variables:

Code:

#define _MAX(a,b)    a > b ? a : b  // yes, I know this is naive and error prone, it's just for demonstration