CS 240: Data Structures

CS 240: Data Structures Thursday, June 7th Programming Semantics, Software Life Cycle, Memory Allocation

Decomposition • When you create a decomposition (and particularly when you create a specification) it should be readable to the point that if someone else was looking at it they could code it.

Concerns • Using classes: We will start discussing this today and using them in the next lab and successive classes. • There is no class on Tuesday, June 12th. I will not have office hours on that day either. • Exam: We will start talking about this on the 19th.

Concerns • Functions: • We use these to solve our problems • Functions are created from our decomposition and specifications. • Functions have an input and an output • These inputs and outputs may be constrained • What goes into a blender? What comes out? • What are the inputs into makepizza(…)? • There may also be side effects: • Blenders use electricity • makepizza(…) destroys my supplies!

Concerns • File Layout: • A program may consist of many, many files. • .cpp, .h, .hpp, .rc, .ico, .jpg, .wav, .dll and so on. • These represent the code as well as other resources needed by the program • Our programs will be more limited in scope: • Our main() will have its own .cpp file. • This .cpp file will use #include to put together a larger project • Each other file is broken up into two parts: • .h file for the function prototypes and #ifndef code • .cpp file the function definitions

blackjack.cpp Contains our main() Contains: #include”card.h” #include”deck.h” #include”player.h” #include”game.h” The following files organize our code: Card -> card.h and card.cpp Deck -> deck.h and deck.cpp Player -> player.h and player.cpp Game -> game.h and game.cpp File Layout Example

More on pointers • Pointers allow us to give data to functions • They also allow us to obtain additional memory resources while a program is running.

Value model: A copy of the data is given. This is like burning a copy of a CD to give to a friend because they don’t have clean hands. This is the model that Java uses. int myfunction(int first, int last, double appliedvalue, float secondvalue); Passing data:

Passing data: • Reference model: • This model allows us to share/give data to a function.

#include<iostream> #include”swap.h” using namespace std; int main() { int number = 5; int secondnum = 10; swap(&number,&secondnum); cout << number << endl; cout << secondnum << endl; return 0; } Output: 10 5 Reference passing

swap.h #ifndef SWAP_H #define SWAP_H //Swaps the values pointed to by the parameters. //input: two int pointers //output: none //side effects: the values pointed to by the two parameters are swapped. void swap(int *a, int *b); #endif swap.cpp #include”swap.h” void swap(int *a, int *b) { int temp = *a; *a = *b; *b = temp; } Reference passing

Using arrays • Arrays are a representation of multiple data of the same type: • Either: int numbers[1000]; or • int number1,number2,number3….. • An array is not just a cleaner scheme but much more modifiable. • Also, easier to access (try setting each of the numbers to 15).

Arrays • An array is implicitly a pointer (a static pointer). • Because it is static, we do not use it as we do with pointers. • Generally, we use dynamic arrays which are created differently.

Dynamic Arrays #include<iostream> using namespace std; int main() { int *numbers; int userinput; cin >> userinput; numbers = new int[userinput]; cout << “Array created of size: “ << userinput <<endl; delete [] numbers; }

Dynamic Arrays • If the array the user asked for isn’t large enough? • Lets say the user inputs: 10 • And we change the code to take in int inputs until the user inputs -1.

Dynamic Arrays #include<iostream> using namespace std; int main() { int *numbers; int userinput; cin >> userinput; numbers = new int[userinput]; cout << “Array created of size: “ << userinput <<endl; int location = 0; userinput = 0; while(userinput != -1) { cin >> userinput; numbers[location] = userinput; location++; } delete [] numbers; }

Dynamic Arrays • When the user inputs the 11th value, it uses memory that isn’t ours. • It may not cause an error right away. • In fact, on larger programs, we might just overwrite our own data for awhile. • Dynamic arrays allows us to resize the array if we need to.

#include<iostream> using namespace std; int main() { int *numbers; int userinput; cin >> userinput; numbers = new int[userinput]; cout << “Array created of size: “ << userinput <<endl; int location = 0; int maxsize = userinput; userinput = 0; while(userinput != -1) { cin >> userinput; numbers[location] = userinput; location++; if(location>=maxsize) { ….. } } delete [] numbers; } int *temp = new int[maxsize*2]; for(int i=0;i<maxsize;i++) { temp[i]=numbers[i]; } maxsize *= 2; delete [] numbers; numbers = temp;

Abstract Data Types • An abstract data type (ADT) is a collection of data. • It provides a representation for some more abstract object. class computer { string name,processor_type,brand,video_card; int processor_speed,ram_speed,ram_amount; …. };

ADTs • This allows you to use the ADT instead of defining each field in your code

ADTs #include<iostream> #include”computer.h” using namespace std; int main() { computer mycomputer; mycomputer.ram_amount = 1024; computer *mycomputer_ptr = new computer; mycomputer_ptr->ram_amount = 1024; cout << mycomputer << endl; //This doesn’t work! return 0; }

ADTs • You could print out each field/value/variable within computer. • However, that would be excessive. • Also, what if you want to change what you decided to print? You’d have to change it in every location. • computer can be given functions/methods that generate a printable output.

ADTs - Output • Option 1: • Create a function that uses cout directly: • This is not preferred, it limits what can be done with the output. • Option 2: • Overload “<<“, that way we can use cout on computer. • This is easier to use, but still limits what can be done with the output. • Option 3: • Create a function that returns a string of what we want to output. • We will use options 2 and 3 in this class

computer.h #ifndef COMPUTER_H #define COMPUTER_H class computer { string name,processor_type,brand,video_card; int processor_speed,ram_speed,ram_amount; public: string getoutput(); }; #endif

computer.cpp #include”computer.h” string computer::getoutput() { string retval = “”; retval = “Computer: “ + name; return retval; }

Other ADT benefits • An ADT allows us to group data together. This way everything we want to manipulate is close together. • The variables/fields declared in the class prototype are “global” to all the class functions/methods.

ADT constraints • Generally, you don’t give a user access to your variables/fields. • They could mess things up, so, mutators and accessors are created. • Mutators mutate/change data. • Accessors access data. • ADTs may require constructors and destructors

int main() { computer mycomputer; mycomputer.set_ram_amount(1024); computer *mycomputer_ptr = new computer; mycomputer_ptr->set_ram_amount(1024); cout << mycomputer.getoutput() << endl; cout << mycomputer.get_ram_amount() <<endl; return 0; }

Constructors/Destructors • Constructors: • Allow you to provide initial values • These are needed for dynamic memory within an ADT • Destructors: • If you have any dynamic memory in the ADT, this is where you deallocate it.

computer.h #ifndef COMPUTER_H #define COMPUTER_H class computer { string name,processor_type,brand,video_card; int processor_speed,ram_speed,ram_amount; int *somedynamicmemory; public: string getoutput(); //provides output computer(); //constructor ~computer(); //destructor }; #endif

computer.cpp #include”computer.h” string computer::getoutput() { string retval = “”; retval = “Computer: “ + name; return retval; } computer::computer() { somedynamicmemory = new int[100]; brand = “No name brand, inc.”; processor_speed = 0; } computer::~computer() { delete [] somedynamicmemory; }

Class Project • We will go over the implementation of a card game as a class. • We will implement either: • Triple Triad, http://en.wikipedia.org/wiki/Triple_Triad#Triple_Triad • Tetra Master http://en.wikipedia.org/wiki/Triple_Triad#Tetra_Master • There are some common features of each which we can work on before we make a decision of which game to implement. • We will take a vote on it next Thursday.

CS 240: Data Structures