C - Pointer Arithmetic causing problems as opposed to standard [] way-CodePudding

I'm new to C and learning it for a class right now. We are currently working on a little project and we are supposed to use pointer arithmetic to access arrays as opposed to the standard [] way.

For some reason, I can use it just fine on the first loop (see code) but when I use it in the second, it doesn't produce the same outcome as if I were to use the standard [] way.

    for (int i = 0; i < size; i  ) {
        for (int j = 0; j < size; j  ) {
            int num = *(*array i) j;
            //Irrelevant code
         }
    }

    for (int i = 0; i < size; i  ) {
        for (int j = 0; j < size; j  ) {
            int num = array[j][i]; // Error comes if I do *(*array j) i;
            //Irrelevant code
         }
    }

I don't know if I am missing something here but why would calling the array using pointer arithmetic be different between the 2 loops?

CodePudding user response：

The equivalence between subscripts and pointer notation is:

a[i] == *(a   i)

You are using (*a i) in place of the correct *(a i).

I believe your first set of loops should read:

for (int i = 0; i < size; i  ) {
    for (int j = 0; j < size; j  ) {
        int spot = *(*(board i) j);
        for (int k = j   1; k < size; k  ) {
            if (spot == *(*(board   i)   k) && spot > 0) {  
                 return 0; 
            }
        }
    }
}

However, since you've not provided an MCVE (Minimal, Complete, Verifiable Example — or MRE or whatever name SO now uses) or an SSCCE (Short, Self-Contained, Correct Example — the same idea by a different name), I can't easily test the code.

Also, now you know why it is better to use the explicit subscript notation; it is a lot harder to get it wrong.