title: defining a 2D array with malloc and modifying it
body: <p>How do i define a 2D array using malloc ? (lets say 10X20).</p>
  
  <p>second, can i increase number of rows or cols without creating a new increased array and copying all data to it?</p>
  
  <p>for instance, how do i allocate memory so the array will be 10x30 or 15x20?</p>
  
  <p>thank!</p>