title: use malloc out of main
body: <p>I need to declare a global big sized array.
  I tried to use malloc out ouf main:</p>
  
  <pre><code>#include &lt;stdio.h&gt;
  #include &lt;math.h&gt;
  #include &lt;stdlib.h&gt;
  #include &lt;string.h&gt;
  #define LENGTH 200000
  
  double *u_data = malloc(LENGTH * sizeof(double));
  double *u_data_old = malloc(LENGTH * sizeof(double));
  double *psi = malloc(LENGTH * sizeof(double));
  
  void main(void){
  
      free(u_data);
      free(u_data_old);
      free(psi);
  }
  </code></pre>
  
  <p>but I receive this error: initialiser element is not constant.
  Does anyone know how to solve this problem?</p>