7.23 C++ How to Program (8th Edition) By Paul Deitel, Harvey Deitel

(Turtle Graphics) The Logo language, which is popular among elementary school children, made the concept of turtle graphics famous. Imagine a mechanical turtle that walks around the room under the control of a C++ program. The turtle holds a pen in one of two positions, up or down. While the pen is down, the turtle traces out shapes as it moves; while the pen is up, the turtle moves about freely without writing anything. In this problem, you’ll simulate the operation of the turtle and create a computerized sketchpad as well.

Use a 20-by-20 array floor that is initialized to false. Read commands from an array that contains them. Keep track of the current position of the turtle at all times and whether the pen is currently up or down. Assume that the turtle always starts at position (0, 0) of the floor with its pen up. The set of turtle commands your program must process
Solution:

 
#include <iostream>
 
using std::cin;
using std::cout;
using std::endl;
 
void turtle(int, int, int);
void print(void);
void direction(int command);
unsigned char floor[20][20] = {'_'}; // initial empty floor
enum Direct {UP, RIGHT, DOWN, LEFT}; // possible turtle directions
Direct go = RIGHT;
int command;
int step;
int posY = 0;
int posX = 0;
bool pen = 0; // initial pen position is up
 
int main()
{
   // array initialization
   for(int i = 0; i < 20; i++)
   {
      for(int j = 0; j < 20; j++)
      {
         floor[i][j] = '.';
      }
   }
 
   // start program
   cout << "Please enter commands: ";
   cin >> command;
 
   // get commands
   while(command != 9)
   {
      // pen status update
      if(command == 2)
      {
         pen = 1;
         cout << "Pen down" << endl;
      }
      else
         if(command == 1)
         {
            pen = 0;
            cout << "Pen up" << endl;
         }
 
      // direction
      if(command == 3 || command == 4)
         direction(command);
 
      // check move
      if(command == 5)
      {
         cout << "Enter \",\" symbol and then step length" << endl;
 
         char com;
         cin >> com;
 
         while(com != ',')
         {
            cout << "\nPlease enter \",\" symbol and then step length";
            cin >> com;
         }
         cout << "\nStep length: ";
         cin >> step;
 
         if(go == RIGHT)
         {
            while((posX + step) > 20)
            {
               cout << "You are going out of floor(right)."
                  << "Please enter less number:" << endl;
               cin >> step;
            }
         }
         else if(go == DOWN)
         {
            while((posY + step) > 20)
            {
               cout << "You are going out of floor(down)."
                  << "Please enter less number:" << endl;
               cin >> step;
            }
         }
         else if(go == UP)
         {
            while((posY - step) <= 0)
            {
               cout << "You are going out of floor(up)."
                  << "Please enter less number:" << endl;
               cin >> step;
            }
         }
         else
         {
            while((posX - step) <= 0)
            {
               cout << "You are going out of floor(right)."
                  << "Please enter less number:" << endl;
               cin >> step;
            }
         }
 
         turtle(step, posY, posX);
         cout << "Your current position: " << posY << ":" << posX << endl;
      }
 
      // print result
      if(command == 6)
         print();
 
      cin >> command;
 
   }
   return 0;
}
 
// go turtle go
void turtle(int a, int posy, int posx)
{
   if(go == RIGHT)
   {
      for(int i = posy; i == posy; i++)
      {
         for(int j = posx; j < posx + step; j++)
         {
            if(pen == 1)
               floor[i][j] = 'X';
            else
               floor[i][j] = '-';
         }
      }
      posX += step - 1;
   }
   else if(go == DOWN)
   {
      for(int i = posy; i < posy + step; i++)
      {
         for(int j = posx; j == posx; j++)
         {
            if(pen == 1)
               floor[i][j] = 'X';
            else
               floor[i][j] = '-';
         }
      }
      posY += step - 1;
   }
   else if(go == LEFT)
   {
      for(int i = posy; i == posy; i++)
      {
         for(int j = posx; j > posx - step; j--)
         {
            if(pen == 1)
               floor[i][j] = 'X';
            else
               floor[i][j] = '-';
         }
      }
      posX -= step - 1;
   }
   else if(go == UP)
   {
      for(int i = posy; i > posy - step; i--)
      {
         for(int j = posx; j == posx; j++)
         {
            if(pen == 1)
               floor[i][j] = 'X';
            else
               floor[i][j] = '-';
         }
      }
      posY -= step - 1;
   }
 
}
 
// Print the 20-by-20 array
void print()
{
   for(int i = 0; i < 20; i++)
   {
      for(int j = 0; j < 20; j++)
      {
         cout << floor[i][j];
      }
      cout << endl;
   }
}
 
// determine directions
void direction(int command)
{
   if(go == RIGHT)
   {
      if(command == 3)
      {
         go = DOWN;
         cout << "Right turn.\Your direction: " << go << endl;
      }
      else
         if(command == 4)
         {
            go = UP;
            cout << "Left turn.\Your direction: " << go << endl;
         }
   }
   else if(go == DOWN)
   {
      if(command == 3)
      {
         go = LEFT;
         cout << "Right turn.\Your direction: " << go << endl;
      }
      else
         if(command == 4)
         {
            go = RIGHT;
            cout << "Left turn.\Your direction: " << go << endl;
         }
   }
   else if(go == LEFT)
   {
      if(command == 3)
      {
         go = UP;
         cout << "Right turn.\Your direction: " << go << endl;
      }
      else
         if(command == 4)
         {
            go = DOWN;
            cout << "Left turn.\Your direction: " << go << endl;
         }
   }
   else
   {
      if(command == 3)
      {
         go = RIGHT;
         cout << "Right turn.\Your direction: " << go << endl;
      }
      else
         if(command == 4)
         {
            go = LEFT;
            cout << "Left turn.\Your direction: " << go << endl;
         }
   }
}