Wherever a constant is legal in a program, There also will a variable be legal, And even more: There also will a formula be legal.

Transcription

1 ORTHOGONALITY Page 1 The Principle 1:36 PM The PRINCIPLE of orthonality says: Wherever a constant is legal in a program, There also will a variable be legal, And even more: There also will a formula be legal. A very simple example of this principle will now be provided. Consider a program which reads an integer from the user and then prints out three times that user's number. The main method code for this program might be: int answer = 3 * number; This example will apply ORTHOGONALITY to the constant 3 that appears in the formula for the answer.

2 ORTHOGONALITY Page 2 Constant to Variable 1:46 PM Here is the program from the previous slide: int answer = 3 * number; We will use ORTHOGONALITY to replace the 3 by a variable named multer. However, this BREAKS the program because the computer is not told what value the variable multer has. This is fixed below:

3 ORTHOGONALITY Page 3 Why Bother 2:00 PM Here is the most recent version of the program steps being discussed: This likely seems a silly way to tell the computer to multiply by 3 - sort of traveling around your elbow to get from your shoulder to your thumb. The scheme above - using a variable, but actually having a constant in that variable is known as: Hard Coding We say that the decision of what to multiply the user's number by is "hard coded". But you already know (from previous homeworks) at least two other ways to get a value into the variable multer: (1) ask the user for its value and employ nextint or (2) arrange multer to be the variable in an arithmetic loop. And there is no end of other possible ways to get a value into multer.

4 ORTHOGONALITY Page 4 User Provided 2:07 PM Here again is the code under discussion: But instead of hard coding a 3 into multer, let us employ a user interaction to get a number into multer: out.print("what multiplier: "); int multer = cin.nextint(); However, this DOES change the behavior of the program - it is NO LONGER an answer to the original problem. To see what this new behavior is, you need to create a program with the above main method code and TRY IT OUT - until you understand what is going on!!! NOBODY else can do this for you!!!

5 ORTHOGONALITY Page 5 Loop Model 2:13 PM Here again is the multiply by 3 program: Below is an Arithmetic Loop model that moves the variable multer through the series of values: 10, 15, 20, 25, 30, 35 int multer = 10; while(multer<=30) { // repeated code goes here multer = multer + 5; } Since it is a model, it is incomplete. Someone needs to put some code in place of the // comment In fact, we can use the code at the top of this slide - but omitting the hard coded 3 command - since, after all, this discussion is about alternatives to hard coding.

6 ORTHOGONALITY Page 6 Loop Provided 2:20 PM Here again is the multiply by 3 program: Here is the Loop Model int multer = 10; while(multer<=30) { // repeated code goes here multer = multer + 5; } And here is the result of combining them: int multer = 10; while(multer<=30) { // repeated code can be seen above multer = multer + 5; }

7 ORTHOGONALITY Page 7 Conclusions 2:27 PM Try out the code from the previous slide - make sure you understand what it does and how it works. Actually write and run the program. NOTE: the code in the previous slide is an example of one model NESTED inside of another model. This kind of combination is VERY COMMON in program development. In many cases there may be five or more models nested one inside another. It is VERY IMPORTANT that you GET NESTING However, there is another way to combine models that is less complex: Write the first model at the top. Write the second model underneath it. That combination is called SEQUENTIAL. A few other combinations are ALTERNATE and CONCURRENT - neither explained here.