C++ Assignment 10
Etch-A-Sketch

Background:

In this assignment you will create an electronic version of the Etch-A-Sketch. This program will give you practice with switch statements, if statements and graphics.

Selection in C++

if (Condition)
  Statement1
else
  Statement2

Here's a fragment of code that displays "Positive":

int nNum = 3;
if (nNum > 0)
     cout<<"Positive"<<endl;
else if (nNum < 0)
     cout<<"Negative"<<endl;
else
     cout<<"Zero"<<endl;

Notice that there is no condition with an else. Just as with loops, if you want more than one line of code to be controlled by an if or an else, make a block of code surrounded by curly braces {} .

If you have only a single statement that you want to execute conditionally, you can leave off the else part, as shown in the following example:

if (nNum == 4)
  cout<<"Four"<<endl;

Similar to the if-else, the switch statement is specifically designed to work with a list of many choices. Here's a fragment of code that displays "Average":

char cGrade = 'C';
switch (cGrade) 
{
  case 'A':
    cout<<"Excellent"<<endl;
    break;
  case 'B':
    cout<<"Good"<<endl;
    break;
  case 'C':
    cout<<"Average"<<endl;
    break;
  case 'D':
    cout<<"Needs Improvement"<<endl;
    break;
  default:
    cout<<"Needs Lots Of Improvement"<<endl;

}

Note that switch only works with variables that can be represented by integers. You can switch on ints, chars and colors, but not doubles, strings or conditions. Each case ends in a colon. Also note the break; at the end of each case.

Since this is a larger program than the previous assignments, you may want to complete it in steps.

Step One:

Here is some pseudocode for the main function:

1. Open a graphics window.
2. Declare three local variables: two integers for the X & Y coordinates of the stylus and a character variable to hold the Key pressed by the user
3. Do while the key pressed is not 'q'
   1. Use getch() to store the key pressed in the local character variable
   2. Switch on the key pressed.
      1. The key pressed means left
         1. decrease the X coordinate by one
      2. The key pressed means right
         1. increase the X coordinate by one
      3. The key pressed means up
         1. increase the Y coordinate by one
      4. The key pressed means down
         1. decrease the Y coordinate by one
      5. The key pressed means clear the screen
         1. Call the cleardevice() function to erase the screen
   3. draw a point at the current coordinates.
4. use closegraph(); to close the graphics window
5. return 0

Step Two:

To make a red border that looks like a traditional etch-a-sketch you can use the bar function from winbgim.h. The bar function takes four arguments that are the coordinates for the four corners of a rectangle in the order left, top, right, bottom. To make a solid red bar acrss the top of the screen try:

	setfillstyle(1,RED);
   	bar(0,0,640,50);

You can use three more calls to the bar function to finish your border.

To make the white knobs at the two bottom corners of the screen the fillellipse function from winbgim.h works well. To make a knob in the lower left of the screen try:

	setfillstyle(1,WHITE);
     	fillellipse(25, 455, 15, 15);

	settextstyle(5, 0, 2);
	//takes three arguments, the first is font style, last is size
	settextjustify(1, 1);
	setcolor(WHITE);
	outtextxy(320, 20, "Etch-A-Sketch");
	//takes three arguments, the first two are coordinates and the third a string

It's a good idea to place all the code that clears the screen, draws the border and displays the instructions in the same function.

Extensions: