showMap()

1. In addition to the ReadMap(int n) function, separate the code for displaying the map in Showmap().
2. Define a global variable "scale" with initial value 1. User can press the '+' and '-' key to increase/decrease the size of the map. For example, when scale = 1, the original map is
   .

   When scale=3, each cell is displayed as a 3x3 block.
   .

3. Assume MAX_ROW=25 and MAX_COLUMN=80. Be sure to check the value of scale to prevent it from being too large or too small (becoming 0).