Lesson 7: Graphics (cont) Ricardo Salazar, Pic 10A

Transcription

1 Lesson 7: Graphics (cont) Ricardo Salazar, Pic 10A

2 (2.8) Graphics Window (Input) cwin can output shapes and text. E.g. cwin << acircle; or cwin << amessage; It can also be used to get input which includes: Text Numbers Mouse clicks The syntax cwin >> myobject does not work Instead, use member functions: cwin.function() The prompt and response are shown at the top of the window.

3 Getting text: cwin.get_string() The member function get_string() reads a string. It needs a message [string] to display. It prompts the user for input. It returns a string. Example: string name = cwin.get_string("enter text: "); The header #include <string> is not needed because it is used by ccc_win. The prompt and user input (at the top) cannot be moved, so plan accordingly. For text inside the window use the Message class.

4 Getting numbers: cwin.get_double() and cwin.get_int() The function cwin.get_double() reads a number. It needs a message to display. It prompts the user for input. It returns a double. To grab integers use cwin.get_int(). It works in a similar fashion. Examples: int x = cwin.get_int("enter an integer: "); double y = cwin.get_double("enter a decimal: ");

5 Getting mouse clicks: cwin.get_mouse() The location of a click can also be obtained. Use the member function cwin.get_mouse() It needs a message to display. It returns an object in the Point class. The prompt appears at the top of the screen. The coordinates also appear at the top, they update with the movement of the mouse. Example: Point p = cwin.get_mouse("click on the screen.");

6 Examples What does the following program do? All inputs as well as the prompt are displayed at the top of the graphics window. Plan your graphics. Leave some space at the top or it will get covered by the prompt. What does the following code do? string name = "El chavo del 8"; name = cwin.get_string(name); cwin << Message( Point(0,0), name );

7 cwin: Member functions Member function cwin.coord( double x1, double x2, double y1, double y2 ) cwin << x Description Sets the viewing area (window) with top left corner (x1,y1) and bottom right corner (x2,y2). Displays the object x (a point, circle, line or message). cwin.clear() string cwin.get_string(string s) int cwin.get_int(string s) double cwin.get_double(string s) Point cwin.get_mouse() Erases the contents of the viewing area. Displays string s at the top and returns the entered string. Displays string s at the top and returns the entered integer. Displays string s at the top and returns the entered double. Displays string s at the top and returns the mouse click Point.

8 More examples After 5 clicks Initial display

9 Decisions, decisions Suppose we want to draw a dart board. Then ask the user to click on it and keep track of the score depending on where the user clicked. First we should draw the board, for example, by displaying 3 concentric circles centered at (0,0) with labels 10, 5 and 1. Problem: How do we figure out how many points to report? Solution: It depends on which circle the click lies in. If the click lies in the inner circle we should add 10 to the score, if on the other hand it lies in the mid circle the score should be increased by 5. Lastly, if it lies on the outer circle the scores changes by one. Needless to say that the score remains the same if the user clicks outside the circles. If we only had a way to tell this to the computer

10 Pseudo-code Sometimes we know how to solve a problem but do not know how to implement (i.e., code) the solution. In these cases writing the steps needed to complete the task could be of great help. A combination of known code and clear steps in plain language is called pseudo-code. In the dartboard example: int score // keeps track of the score if (inside smallest circle) score += 10 if (outside smaller but inside medium circle) score += 5 if (outside medium but inside big circle) score += 1 in any other case leave score untouched

11 Boolean * statements A boolean statement is one that can be evaluated as true or false, and are useful for decision purposes. ( 2 < 3 ) is a true statement; ( 2 > 3 ) is a false statement. Boolean variables store the values of such statements. bool b = 2 < 3 ; // sets b = true A common representation is 1 = true and 0 = false. The following lines are equivalent: bool my_boolean = (2 < 3); bool my_boolean = true; bool my_boolean = 1; * Named after George Boole (Logician, ).