Using #define in C Program

Question

I am trying to use #define to define a constant in my program. I realize I could use const, but I am trying to get a good understanding of #define. Could someone please explain why the following code does not work, and should be done instead?

#include <stdio.h>
#define M 20;
typedef int Marray_t[M][M]; //I can't define an M x M array
int main() {
 Marray_t A;
 int i;
 for (i = 0; i < M; ++i) { //Can't iterate up to M
 A[i] = i;
 }
 return 0;
}

Answer 1

You must remove ; after20, like this

#define M 20

• Oliver Spryn: Oh... it was defining it as 20;. I totally didn't think of that! Thank you.
• MrMesees: Also if like me you are an idiot and put = assignment in define, try removing it. This shows how much I dislike defines and how I don't use C enough any more.