C preprocessor #if expression

I am a bit confused on the type of expression we can use with the #IF preprocessor in the C language. I tried the following code, and it isn't working. Please explain and provide examples for expressions that can be used with the preprocessor.

#include<stdio.h>
#include<conio.h>
#include<stdlib.h>

int c=1;

#if c==1
    #define check(a) (a==1)?a:5
    #define TABLE_SIZE 100
#endif

int main()
{
    int a = 0, b;
    printf("a = %d\n", a);
    b = check(a);
    printf("a = %d %d\n", a, TABLE_SIZE);
    system("PAUSE");
    return 0;
}