plot.cpp

来自「数据结构与程序设计教材源码 数据结构与程序设计教材源码」· C++ 代码 · 共 142 行

 
int Plot::get_print_col(double x_value)
{
   double interp_x = ((double) max_col) * (x_value - x_low) / (x_high - x_low) + 0.5;
   int answer = (int) interp_x;
   if (answer < 0 || answer > max_col) answer = -1;
   return answer;
}
 
int Plot::get_print_row(double y_value)
/* 
 
Post:
Returns the row of the screen at which a point with
y-coordinate y_value should be plotted, or
returns -1 if the point would fall off the edge of
the screen.
 
*/
{
   double interp_y =
      ((double) max_row) * (y_high - y_value) / (y_high - y_low) + 0.5;
   int answer = (int) interp_y;
   if (answer < 0 || answer > max_row) answer = -1;
   return answer;
}
 
Error_code Plot::set_limits()
{
   double x, y;
   double new_increment = x_increment,
      new_x_low = x_low,
         new_x_high = x_high,
            new_y_low = y_low,
               new_y_high = y_high;
   cout << "Give a new value for x increment. Previous value = " << x_increment;
   cout << "\n Enter a value or a new line to keep the old value: " << flush;
   if (read_num(x) == success) new_increment = x;
   cout << "Give a new value for lower x limit. Previous value = " << x_low;
   cout << "\n Enter a value or a new line to keep the old value: " << flush;
   if (read_num(x) == success) new_x_low = x;
   cout << "Give a new value for upper x limit. Previous value = " << x_high;
   cout << "\n Enter a value or a new line to keep the old value: " << flush;
   if (read_num(x) == success) new_x_high = x;
   cout << "Give a new value for lower y limit. Previous value = " << y_low;
   cout << "\n Enter a value or a new line to keep the old value: " << flush;
   if (read_num(y) == success) new_y_low = y;
   cout << "Give a new value for upper y limit. Previous value = " << y_high;
   cout << "\n Enter a value or a new line to keep the old value: " << flush;
   if (read_num(y) == success) new_y_high = y;
   if (new_increment <= 0 || new_x_high <= new_x_low || new_y_high <= new_y_low)
      return fail;
   x_increment = new_increment;
   x_low = new_x_low;
   x_high = new_x_high;
   y_low = new_y_low;
   y_high = new_y_high;
   return success;
}
 
void Plot::clear()
{
   points.clear();
}
 
void Plot::find_points(Expression &postfix)
/* 
 
Post:
The Expression postfix is evaluated for values of
x that range from x_low to x_high in steps of
x_increment.  For each evaluation we add a Point 
to the Sortable_list points.
Uses:
Classes Token, Expression, Point, and List.
 
*/
{
   double x_val = x_low;
   double y_val;
   while (x_val <= x_high) {
      Token::set_x(x_val);
      postfix.evaluate_postfix(y_val);
      postfix.rewind();
      Point p(get_print_row(y_val), get_print_col(x_val));
      points.insert(0, p);
      x_val += x_increment;
   }
}
 
void Plot::draw()
/* 
 
Post:
All screen locations represented in points have
been marked with the character '#' to produce a
picture of the stored graph.
Uses:
Classes Point and Sortable_list and its method merge_sort.
 
*/

{
   points.merge_sort();
   int at_row = 0, at_col = 0;         //  cursor coordinates on screen

   for (int i = 0; i < points.size(); i++) {
      Point q;
      points.retrieve(i, q);
      if (q.row < 0 || q.col < 0) continue;  //  off the scale of the graph
      if (q.row < at_row || (q.row == at_row && q.col < at_col)) continue;

      if (q.row > at_row) {                  //  Move cursor down the screen.
         at_col = 0;
         while (q.row > at_row) {
            cout << endl;
            at_row++;
         }
      }

      if (q.col > at_col)                    //  Advance cursor horizontally.
         while (q.col > at_col) {
            cout << " ";
            at_col++;
         }
      cout << "#";
      at_col++;
   }
   while (at_row++ <= max_row) cout << endl;
}
 
Plot::Plot()
{
   x_low = -10;
   x_high = 10;
   y_low = -1000;
   y_high = 1000;
   x_increment = 0.01;
   max_row = 19;
   max_col = 79;
}