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copied!<p>Your <code>for</code> loop:</p> <pre><code>for(int i=0;i<6*p;i++) </code></pre> <p>Treats the array size as <code>6*p</code> where in the example <code>p==9</code>. So your loop treats the array size as 54.</p> <p>But array <code>a</code> has only 18 elements so your initialisation is overflowing this array.</p> <p>Array <code>b</code> has only 36 elements so your initialisation is overflowing this array as well.</p> <p>Overflowing an array will write to memory that you probably do not intend to write to, which can cause all sorts of bugs...</p> <p>You would be better to use a function like. Also do you need to <strong>NULL-terminate</strong> your strings?</p> <pre><code>void initialize(char a[], size_t aSize, char b[], size_t bSize) { int i = 0; for(; i < aSize-1; i++) a[i]='-'; for(i = 0; i < bSize-1; i++) b[i]='-'; // I think you need to NULL terminate.... a[aSize-1] = '\0'; b[bSize-1] = '\0'; } int main() { int p=9; char a[2*p],b[4*p]; initialize(a, sizeof(a), b, sizeof(b)); std::cout << a << std::endl << b << std::endl; return 0; } </code></pre> <p>Or even more generically in you <code>main()</code> function if you ever use arrays that are <em>not</em> of type <code>char</code>...</p> <pre><code>initialize(a, sizeof(a)/sizeof(a[0]), b, sizeof(b)/sizeof(b[0])); </code></pre> <p>Or even, to initialise the arrays just use <a href="http://www.cplusplus.com/reference/cstring/memset/" rel="nofollow"> <strong><em>memset()</em></strong></a> and then you won't need the function <code>initialize()</code> :) </p> <p>E.g.</p> <pre><code>#include <string.h> int main() { int p=9; char a[2*p],b[4*p]; memset(a, '-', sizeof(a)-1); a[sizeof(a)-1] == '\0'; memset(b, '-', sizeof(b)-1); b[sizeof(b)-1] == '\0'; std::cout << a << std::endl << b << std::endl; return 0; } </code></pre> <p>The other thing I just though of was "are you <strong>NULL-terminating</strong> your strings? I've changed the above examples to cater for that, otherwise when printing the string the print function won't know where to stop!</p> <p>Yet another option might also be <a href="http://www.cplusplus.com/reference/algorithm/fill/" rel="nofollow"><strong><em>std::fill()</em></strong></a> or <a href="http://www.cplusplus.com/reference/algorithm/fill_n/" rel="nofollow"><strong>*std::fill_n()*</strong></a>:</p> <pre><code>#include <iostream> #include <algorithm> // std::fill int main(int argc, char* argv[]) { int p=9; char a[2*p],b[4*p]; std::fill_n(a, sizeof(a)-1, '-'); a[sizeof(a)-1] = '\0'; std::fill_n(b, sizeof(b)-1, '-'); b[sizeof(b)-1] = '\0'; std::cout << a << std::endl << b << std::endl; return 0; } </code></pre>

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