CST112--Functions Page 1

Transcription

1 CST112--Functions Page Processing: Functions CST112 Structuring Programs (Modularity) Programmers often divide large applications into several modules within program This is necessary due to size and complexity of professional programs Hierarchies of structure allow design to begin at most general level And work to more specific To Find an Office in a Building A city has many districts or suburbs each of which has many streets each of which has many buildings»each of which has many offices Top-Down Program Structure problem has some major tasks each of which has many subtasks each of which has many subtasks and so on down as needed Structure Using Functions (Page 1) Complete applications in programming consist of a hierarchical collection of functions Working toger y perform entire programming task Most complex tasks can be subdivided into procedures in this way ( divide and conquer ) Structure Using Functions Functions are written by a programmer to define specific tasks within larger task Each task should be clearly identifiable Statements defining functions are written once in application and may be called from more than one location in program (reusability) Statements and variables are hidden from or functions in program (information hiding) Advantages of Using Functions Pre-written built-in functions (part of Processing language/library) simplify program development E.g. line(), rect(), ellipse(), etc Each small piece can be written and tested separately Smaller functions usually are easier to understand In large professional systems individual programmers and programmer teams can build and share functions Function Call (Page 1) function is invoked by a function call syntax specifies function s name

2 CST112--Functions function at which sub function was called Page At conclusion of execution of sub function, control returns to point in initial Functions1 (Page 1) Functions1 Functions1 Transfers(Page control 3) to location of function in program and executes it Specifications Optionally provides for Functions2 information/input (called arguments) that function needs for execution Draw Stick Man Move Function by adding Call speed (+) to x-coordinate Format: Set speed by finding absolute difference ( ) between current and previous mousex If functionname( x-coordinate is [argument1, at right edge argument2, of output window, ] ); reset x-coordinate to (=) zero (0) Structure function Chart call for will Functions2 transfer control of execution of program to location of functionname Functions2 Examples: (Page 1) Functions2 stickman(); circle(x, y, radius); Functions2 (Page 3) Function Definition (Page 1) Functions2 A program (Page function 4) is defined by a header (which names function also is called its Functions2 signature) and (Page 5) body enclosed in braces format is similar to setup() or draw() Specifications Format: for Functions3 Draw type/ snow functionname (small circles ( in [type white) parameter1, at random type x- and parameter2, y-coordinates ] ) If mouse is pressed, shovel snow (draw larger circles in same color as background) variabledeclarations/statements at current mousex and mousey locations Structure Chart for Functions3 Functions3 Function (Page Definition 1) Examples: Functions3 setup() Mini Quiz No. 1 (Save as FunctionsMiniQuiz1.pde ) Draw a ball inside an output window of 400 x 400 From stickman() draw() function call programmer-defined functions to: Draw ball Move ball right (or left) at given speed Change speed direction (1 or -1) if ball reaches eir left or right edge of Function output Control window Place a comment before each function header 1. function call transfers control to named sub function You must show me that one function is working before you start working on next 2. body of that function is executed entirely one 3. At conclusion of execution of sub function, control returns to point in initial Structure function Chart at which for Mini sub Quiz function No. was 1 called Passing Arguments In function calls, re may be one or more values in parenses (called arguments) which are passed to called function (data sharing ) This is true for built-in Processing function calls as well as those defined by programmers Format: functionname(parameter1[, parameter2, ]); Examples: rect(x, y, w, l); circle(x, y, radius); Parameter List (Page 1) parameter list is a comma-separated list of variable declarations in function header

3 CST112--Functions Page Data Values in Functions4 draw() circle(75, circle(x, y, 125, radius); 50); circle(150, 100, 75); Parameter List (Page 1) parameter list is a comma-separated list of variable declarations in function header textbook calls this argument list However circle(int for x, int clarity y, int and radius) consistency with or languages, we will use term parameter list Variables receive values passed from parameters in function call Parameter List Format: Specifications type/ functionname( for Functions4 [type parameter1, type parameter2, ] ) Draw Each a circle parameter giving in x- list and is a y-coordinates, declared variable, and declared radius separately with its own type (even if two or more parameters are same type) Add (+) to size of radius Examples: If radius is half width of output window, reset radius to zero (0) circle(int x, int y, int radius) Also if radius is half width of output window, reset fill color to random RBG values stickman(int xcoord, int ycoord) Structure Parameter Chart List for Functions4 (Page 3) Parameters are local variables: Functions4 A means (Page for communicating 1) information between function call and function Functions4 itself When function is called, argument values are passed and assigned to Functions4 parameter (Page variables 3) in function header Functions4 Parameter (Page List 4) (Page 4) MiniQuiz number No. of 2 arguments in function call must be same as number of (Specifications parameter variables for Functions5) in called function header Only variable write code type inside of each parameter draw() function: in function header must match that of argument value passed to it (and in same order) x and y variables should be declared locally inside draw() function If function is not passed any argument values, leave parenses empty: Set random values for x- and y-coordinates to within 50 pixels of left, right, top and setup() bottom edges of output window Draw resetradius() Stick Man giving x- and y-coordinate arguments Function If Call mouse and is pressed, Definition set Examples background to white (erases all random Stick Function Men ) calls: MiniQuiz circle(75, No. 125, 2 50); (Structure circle(x, y, Chart r); for Functions5) circle(mousex, mousey, radius); Functions5 (Page 1) Function header (signature) and body Functions5 circle(int (Page x, int 2) y, int radius) Functions5 (Page 3) Functions5 (Page 4) Passing Arguments ByValue Passing an argument by value means that a copy of argument is stored as private in called function at a separate RAM address Changing value of variable in called function does not change original value opposite of passing by value is passing by reference which means that address of values is passed to called function Changing value of variable in called function will change original value

4 CST112--Functions Page original value opposite of passing by value is passing by reference which means that address of values is passed to called function Changing value of variable in called function will change original value Return Values (Page 1) Programmer-defined functions: 1. May have arguments passed to m ( input) 2. Process that data ( code) 3. May have return values ( output from function that is sent back to location of function call) Return Values Many functions calculate a return value (result) that is passed back to calling function Statements using keyword return are used to return a value from function to call location Any number of return statements may be coded within function, any of which: 1. Terminate execution of function at that point 2. Return control to location at which it was called and passes result back to call Return Values (Page 3) Format for functions that return a result: return expression; Returns expression value to calling function Examples: return 10; return x; return mousex * mousey; return random(0, 255); Return Value Example Function call: int rgb = rgbrandom(); Execution of all functions take precedence over assignment operator Function definition: int rgbrandom() return (int) random(0, 255); Using Return Value function call should use returned value as part of anor statement Assignment statement, output statement, or some or data related operation Examples: r = rgbrandom(); println( rgbrandom() );

5 Data Values in Functions6.pde int rgbrandom() draw() int return r; (int) random(0, 255); int rgbrandom() r = 127; if (rgbrandom() < 127) Data fill( return Values rgbrandom(), (int) in random(0, Functions6a.pde rgbrandom(), 255); rgbrandom() ); draw() Invalid Function Calls Function Types refore fill( 127 functions, rgbrandom(), that return rgbrandom() a value should ); not stand alone int Functions rgbrandom() circle(int, that int, return int) function a value have does a not type return a value so following is valid: circle(mousex, A function s type mousey, must rad); be same as type of value that is returned Format: return rgbrandom() (int) random(0, function 255); does return a value so following is invalid: rgbrandom(); type functionname( [parameterlist] ) Example: Function int rgbrandom() int rgbrandom() Types Functions If a value is that not return returned, a value have return a type is A return function s (int) random(0, type must 255); circle(int xcoord, intbe ycoord, same int radius) as type of value that is returned Format: key System Variable Data typevalues functionname( in Functions6a.pde [parameterlist] ) Example: A Processing system variable that stores last character that was used on keyboard draw() (eir keyed or released) int rgbrandom() Special system constants that can be tested for are BACKSPACE, TAB, ENTER, ESC, If a value is not returned, return type is etc. fill( 127, 200, rgbrandom() ); circle(int xcoord, int ycoord, int radius) Examples: if (key System == 'A') Variable A Differentiates Processing system between variable upper that and stores lower cases last character that was used on keyboard if (key == (eir ENTER) keyed // or released) Enter key intspecial rgbrandom() system constants that can be tested for are BACKSPACE, TAB, ENTER, ESC, Functions6.pde (Page 1) etc. Functions6.pde Examples: return (int) random(0, 255); if (key == 'A') Functions6.pde (Page 3) Data Differentiates Values in Functions6a.pde between upper and lower cases Functions6.pde if (key == ENTER) Pythagorean // Enter orem draw() key Functions6.pde sq and sqrt Functions (Page 1) Functions6.pde se fill( are 127 two, Math 200 functions:, 110 ); sq() function returns square of a value, ( product of multiplying it by Functions6.pde itself), i.e. (Page 3) Functions6.pde square = sq(9); Pythagorean // square will orem be 81 sqrt() function returns square root of a value, i.e. int rgbrandom() sq root = sqrt(9); Functions // root will be 3 se are two Math functions: Using Return Value return sq() (int) function random(0, returns 255); square of a value, ( product of multiplying it by A function itself), i.e. call that returns a value can be used to represent values in a larger expression (not just in assignment statements) square = sq(9); // square will be 81 Functions6a Examples: (Page 1) sqrt() function returns square root of a value, i.e. println( rgbrandom() ); Functions6a root = sqrt(9); // root will be 3 circle(x, y, radius(x, y) ); Using Functions6a fill( rgbrandom(), Return Value rgbrandom(), rgbrandom() (Page 3) ); A function call that returns a value can be used to represent values in a larger Data Final Values Review in of Functions6a.pde Calls expression (not just in assignment statements) Examples: So draw() remember that re are three distinct elements involved in calling functions: println( 1) function rgbrandom() call transfers ); control to called function (and automatically circle(x, fill( transfers rgbrandom(), back to y, radius(x, rgbrandom(), call location y) ); rgbrandom() when done ); executing) 2) fill( One or more argument values may be passed to parameter variables that are rgbrandom(), rgbrandom(), rgbrandom() ); defined in called function s header Data 3) A Values value ( in Functions6a.pde result of function s processing) may be returned after its execution MiniQuiz draw() No CST112--Functions Page

6 CST112--Functions Page 6 transfers back to call location when done executing) 2) One or more argument values may be passed to parameter variables that are defined in called function s header 3) A value ( result of function s processing) may be returned after its execution