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POComparing arrays with comparison operator
 

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  1. POComparing arrays with comparison operator
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    <p>This is just a small question, more aimed at understanding the usage of arrays than at solving a difficult problem.</p> <p>I currently have an array of four integers (Neighbors) that I'd like to compare against a set of other arrays (which don't exist anywhere else - I have no need to store them). I want to know which of the four arrays Neighbors is identical to. As somebody who doesn't know any better, my first attempt was to do this:</p> <pre><code>if (Neighbors == {1, 1, 0, 0}) { //code... } else if (Neighbors == {0, 1, 1, 0}) { //code... } else if (Neighbors == {0, 0, 1, 1}) { //code... } else if (Neighbors == {1, 0, 0, 1}) { //code... } </code></pre> <p>As you can see, the order of the integers is important. However, the above returned compiler errors about expecting primary expressions before curly-brace tokens.</p> <p>So instead, I tried this:</p> <pre><code>int Sets[4][4] = { {1, 1, 0, 0}, {0, 1, 1, 0}, {0, 0, 1, 1}, {1, 0, 0, 1} }; if (Neighbors == Sets[0]) { //code... } else if (Neighbors == Sets[1]) { //code... } else if (Neighbors == Sets[2]) { //code... } else if (Neighbors == Sets[3]) { //code... } </code></pre> <p>What happens here is that even when <code>Neighbors = {0, 1, 1, 0}</code> (for example), <code>Neighbors == Sets[1]</code> returns false.</p> <p>Now, after doing this and wondering why, I remembered that the array variable is basically a pointer to the first element in a sequence. Right? So I think I get why the above code doesn't work - I'm comparing two memory addresses, rather than two arrays. So instead I wrote this code, which works fine:</p> <pre><code> for (int ii = 0; ii &lt; 4; ++ii) { bool Same = true; for (int jj = 0; jj &lt; 4; ++jj) { if (Neighbors[jj] != Set[ii][jj]) { Same = false; } } if (Same == true) { //code... } } </code></pre> <p>What I want to know is whether there is a way to compare arrays like this without going through two for-loops. It seems like something that ought to be simpler than this. I know a for-loop isn't especially intensive when you've only got 4 values, but I still would have thought it'd be easier to determine whether two arrays contain identical information. If each array is a contiguous block of memory, I would have thought you could just look at those two blocks and check whether they are identical (which is basically what the for-loops are doing, although that requires doing it manually).</p> <p>So is there a way to compare the content of arrays directly, preferably with a single line of code? If not, why not? I'd like to understand the science behind this issue.</p>
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    1. COJust a tip here - you can add a `break;` statement after your line `Same = false;` this will speed up a little as once you know its false, why continue checking (unless you really want to) ???
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      1. USmathematician1975
    2. COThat's true - I usually do that, but I forgot this time around, since it's such a small set of data. Thanks for the reminder though!
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