#define vs const declaration

[santosh]

#include <stdio.h>
#define MAX 243

int
main(void)
{
printf("MAX = %d\n", MAX);
#undef MAX
#define MAX 18
printf("MAX = %d\n", MAX);

return 0;
}

MAX is not an object. It resolves to a value. It cannot be modified
within a single expression.