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    <p><code>char*</code> isn't quite a <code>char</code>. <code>char*</code> is basically a string (it's what strings were before C++ came along).</p> <p>For illustration:</p> <pre><code>int array[N]; // An array of N ints. char str[N]; // An array of N chars, which is also (loosely) called a string. </code></pre> <p><code>char[]</code> degrades to <code>char*</code>, so you'll often see functions take a <code>char*</code>.</p> <p>To convert <code>std::string</code> to <code>const char*</code>, you can simply call:</p> <pre><code>std::string s; s.c_str() </code></pre> <p>In this case, it's common to use the preprocessor to define your OS. This way you can use the compiler to do the platform specific stuff:</p> <pre><code>#ifdef OS_LINUX const char cls[] = "clear"; #elif OS_WIN const char cls[] = "cls"; #endif </code></pre> <p>One thing you may want to consider is making it a function. This avoids nasty dependencies of <a href="http://www.devx.com/getHelpOn/10MinuteSolution/17803" rel="nofollow noreferrer">global construction order</a>.</p> <pre><code>string GetClearCommand() { if (OS == "LINUX") { return "clear"; } else if (OS == "WIN") { return "cls"; } FAIL("No OS specified?"); return ""; } </code></pre> <p>What it looks like you're trying to do is this:</p> <pre><code>#include &lt;iostream&gt; using namespace std; #ifdef LINUX const char cls[] = "LINUX_CLEAR"; #elif WIN const char cls[] = "WIN_CLEAR"; #else const char cls[] = "OTHER_CLEAR"; #endif void fake_system(const char* arg) { std::cout &lt;&lt; "fake_system: " &lt;&lt; arg &lt;&lt; std::endl; } int main(int argc, char** argv) { fake_system(cls); return 0; } // Then build the program passing your OS parameter. $ g++ -DLINUX clear.cc -o clear $ ./clear fake_system: LINUX_CLEAR </code></pre>
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    1. COPerfect, but within the function that I'm using (within while loops as well..) I need to still call system(cls), with ::cls the compiler fails and says it isn't defined, how would I access the cls constant defined out of scope?
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    2. COI think the thing with `#ifdef` is supposed to be a global (outside of functions). For this usage, I think a plain `const char* cls = "clear"` might also be fine (no need for an array if you just want a reference to a constant literal).
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    3. CO@Jason, edited my answer with an example. You can always look "up-scope" to see variables. Never down-scope.
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