CS201 – Introduction to Computing – Sabancı University 1 Announcements l General rules about...

CS201 – Introduction to Computing – Sabancı University 1

Announcements General rules about homeworks

Use of global variables (variables defined outside of functions) prohibited

No abrupt program termination in the middle of the program. Modularity and code duplication are important

• Code duplication must avoided Common Submission Mistakes

In HW1, some students submitted empty/wrong files• Make sure that you send the cpp file; otherwise we cannot grade

rar format is not allowed for compression; please use zip Do not use blanks, Turkish characters, special symbols in the filenames

• Only English alphabet letters, digits and underscore are allowed Please submit the required files only, not the entire project folder

About HW2 Use of functions

• Proposed functions are just one set of possible function use in such a program

• If you want to use other set of functions, you should be able to demonstrate understanding of modularity and you should be able to avoid code duplication

Midterm 1: November 22, Saturday 10:40 – 12:20 Midterm 2: December 26, Friday, 17:40 – 19:20


Chapter 3 - Continued

Overview of functions sequence of statements with its own local variables supports modularity, reduces code duplication

Data transfer between function to be called and caller function by means of parameters currently one-way

• from caller function into function to be called later we will see how to return data back to the caller

function


Function Prototype (from 2.6) Functions definition has two parts

function heading • name, parameters, return type

function body (local variables and statements within curly brackets)

void display (string name){ cout << “Hello ” << name << endl;}

Like variables, a function must be declared before its first call Problem of function declaration order

• You cannot call a function before you declare it SOLUTION: You may define function prototypes (a copy of the

heading) at the beginning without function declarations


Function Prototype – Example Problem What is the problem below (program order.cpp) ? void Hi (string name)

{ cout << "Hi " << name << endl; Greetings();}

void Greetings(){ cout << "Things are happening inside this computer" << endl;}

int main(){ Hi("Fred"); return 0;}

Greetings() is called in Hi() but it is declared afterwards


Function Prototype – Solution Add function prototypes to the beginning (order2.cpp) #include <iostream>

#include <string>using namespace std;

void Hi (string);void Greetings();

void Hi (string name){ cout << "Hi " << name << endl; Greetings();}

void Greetings(){ cout << "Things are happening inside this computer" << endl;}

int main(){ Hi("Fred"); return 0;}

Prototypes

Function

Declarations


Function Prototypes

!!!Do not forget semicolon after the prototype definition!!! no semicolon after the parameters in normal definition

Sometimes prototypes are not necessary if the order of function calls allows But it is a good programming practice to have them

Parameter names are not needed in prototypes But it is OK if you have the parameter names.

In #included files we have the functions’ prototypes only implementations of function bodies are in libraries or in

other cpp files• they are linked together


Enumerated Types Section 9.3.4 You can define your own type by giving its constant values (literals)

as identifiers type for CardSuit type for colors

Type definition syntax enum TypeName {list of literals separated by comma};

Type definition exampleenum CardSuit {spade, heart, diamond, club};

You can define variables of enum types, you can use them as parameters and return types throughout the cpp file So an enum type must be defined as global (after

using namespace std; and before the function declarations) Such a global type declaration is not a prohibited use of globals.


Enum types Example use

CardSuit c;c = club;

Each constant of an enum type has an associated integer code starting from 0 spade is 0, heart is 1, diamond is 2, club is 3

Displaying an enum type variable actually displays its integer codecout << c; // displays 3

Cannot assign an integer to an enum variablec = 2; //illegalc = CardSuit(2); //legal, c becomes diamond

cannot inputcin >> c; //invalid

can use comparison operators (<, >, <=, >=, ==, !=) The relational operators <, >, <=, >= compare codes

if (c <= heart)cout << "hi" << endl;


Introduction to Classes and Objects (3.4)

In object-oriented programming terminology, a class is defined as a kind of programmer-defined type

From the natural language definition of the word “class”: Collection of members that share certain attributes and

functionality Likewise classes in object-oriented programming

In object oriented programming languages (like C++) classes are used to combine everything for a concept (like date, student) Data (e.g. student id, gpa) Functions (e.g. students enroll, students graduate)


Introduction to Classes and Objects We define variables of types (like int, double). Similarly,

we define objects of classes an object is a member of a class

Why classes and objects? In other words, why object-oriented programming? It gives programmers the ability to write programs using

off-the-shelf components without dealing with the complexity of those components

Saves time and effort

You may design and implement, and later use your own classes, but we will start with using other-programmers-defined classes this is what a programmer generally does


How to Use Classes? The behavior of a class is defined by member functions

(methods) by which objects of that class are manipulated You should know about the member functions and what

they do name of the function parameters and parameter types return type functionality

You don’t need to know how the function is implemented analogy: you can add two int variables using +, but you

don’t need to know how computer really adds more analogy: you can drive cars, but you don’t need to

know how the fuel injection works


Example: Robot Class (not in the book) A class for robots You can create robots (objects) at different locations and facing

different orientations (east, west, south or north) We use “constructor” for this purpose “constructor”: general name for object creating functions

You can change the color of the robot; color is parameter of an enumerated type SetColor member function

Robots can turn right TurnRight member function no parameter

Robots can move at the facing direction Move member function can be used with or without parameters

• without parameter: 1 step• with parameter: parameter is number of steps

more robot functions will be given later


Robot World Robots live on a

world of cells each cell has

a coordinate southwest is

(0,0) point south and

west bounded east and north

unbounded no cells with

negative coordinates


More on robots class and robot world Robot world also allows you to

install/uninstall barriers at cell boundaries plant/remove “things” within cells save, save as, open, run program, etc. (utilities)

Robot world is actually a Windows application it needs two files to be added up to the project

• robots.cpp (robot class and other utilities are implemented)• miniFW.cpp (for windows programming – out of scope of this course)• The file in which you write your main program should be another separate file.• robots.h is to be #included at the beginning of the main program• robots.cpp, miniFW.cpp, robots.h and miniFW.h files should be in the folder as your actual

program file. • project should be win32 application – This is very important!• In such a project, robot world is created automatically even if you do not have anything in

main. When “run” clicked, your program is executed on the current robot world. Important Detail: your main is not actually the main program; actual main (WinMain) is in

robots.cpp, but do not bother with this detail for now. Caution: cin and cout do not work in robot world


simplerobot.cpp – sample program that utilizes robots class

#include "Robots.h"using namespace std;//simple robot test programint main (){

Robot Ali(5, 1); //Ali is a robot at (5,1) location and facing eastAli.SetColor(white); //Ali's color is set to whiteRobot Ayse(5, 8, north);//Ayse is a robot at (5,8) location and facing north Ayse.SetColor(red); //Ayse's color is set to red

Ali.Move(5);

Ayse.TurnRight();Ayse.Move();Ayse.Move();Ayse.TurnRight();Ayse.Move(10);Ali.TurnRight();Ali.TurnRight();Ali.Move(4);

return 0;}


Where is a Class Defined?

Class definition/interface is in a header file (a file with .h extension) member function prototypes and and some other

declarations function implementations are not in this header file

Implementations of the member functions are in a .cpp file Robot example

class definition/interface is in robots.h• that is why it is included in simplerobot.cpp

class implementation is in robots.cpp• part of the project – linked together


robots.h - Definition of class Robot (partial)

#ifndef Robots_h // to avoid duplicate inclusions of robots.h#define Robots_h

// enumerated types for colors and directionsenum Direction { east, west, north, south };enum Color { white, yellow, red, blue, green, purple, pink, orange };

class Robot{ public:

Robot (int x, int y, Direction dir = east, int things = 0); // robot constructor - color yellow, default direction is east, default //things in bag is zero

void Move (int distance = 1); // to move robot, default displacement is 1void TurnRight (); // to turn the robot rightvoid SetColor (Color color); //to change the color of robot

// there are some other functions that we will see later// see next page for the rest of the file

Continued on the next page


robots.h - Definition of class Robot (partial)

private:int xPos; //x-coordinate of the robotint yPos; //y-coordinate of the robotDirection direction; //direction of the robotColor color; //color of the robotint bag; //number of things in the bag of the robotbool stalled; //is the robot dead?bool visible; //is the robot visible on the screen?

//the rest of the private part is out of scope of this course, at least for now

};

#endif


Parts of Class Definition Public

Member functions as seen by programmer Programmer can use the functions defined in the public

section only Constructors

• special member function to create objects (variables)• there might be several constructors with same name, but different

parameters (not the case for Robot class) Private

Mostly the data part of the class Necessary for internal implementation of class

• e.g. xPos, yPos – used by the implementation of Move function, but we do not use it as the programmer using the Robot class

Not accessible by programmer• e.g. in simplerobot.cpp, programmer cannot modify xPos


How to

How to define objects?

class_name object_name_list_separated_by_comma; do not forget arguments for each object, if any.

How to call a member function?

object_name.function_name(arguments); a member function operates on an object for which it is

called.


How to How to use Robot class as a parameter

if you do not change the color, position, orientation etc. of the robot, then use as other types (at least for now – later we will see more efficient ways)void dothis (Robot myrobot, int param)

However, if you change the robot’s characteristics (color, position, orientation, etc.), then you have to use the character & between Robot and the parameter namevoid Go (Robot & myrobot, int x, int y)

Calling such functions is not different• Do not use & while callingRobot rob(5, 6, west);Go (rob, 12, 5);

We will see the & notation in more detail later (Section 6.2.3) this type of parameters are called “reference parameters”

Recommended since you generally

change the robot

characteristics in functions


Some more recommendations Avoid creating robots in user-defined functions

Create all necessary robots in main If needed pass them as parameters to other functions

Addition to scope rules IMPORTANT RULE: An identifier (e.g. an object or a

variable) can be referred only in the compound block in which it is declared

A compound block is the statements and declarations within matching curly brackets

• e.g. after if or else Implication of this rule in robot programs: when a robot

object is created in a compound block, it can be referred only in that block

• Otherwise, undeclared identifier error occurs• Solving this problem by re-creating it is NOT A SOLUTION

if (x>0){ Robot r(x, 0); r.Move(3);}r.Move();

Undeclared identifier


Compiling, Linking Single file case

Linking is necessary to use the libraries for example, iostream for cin and cout, string for string class operations

library functions are defined (prototypes) in header files (#included)

library function bodies are ready in object code • linked

myprog.cpp(source code)

myprog.obj(object code)

compilemyprog.exe

link


Compiling, Linking

several .cpp files user-defined class implementations and some utility

functions can be written in different .cpp files those files are independently compiled and then linked

together to create the executable code• libraries are linked too

int main (){Robot Ali(5, 1); Ali.SetColor(white); Ali.Move(5);return 0;}

simplerobot.cpp

Robot::Robot (int x, int y, {xPos = x;yPos = y;direction = dir;color = yellow;...

robots.cpp

simplerobot.obj

robots.obj

1101010101101010100110010101010 ...

libraries


#include Kind of copy-paste

specified header file is copied before compilation Include file locations

standard ones are in INCLUDE directory under ....\Microsoft Visual Studio\VC98

Tools Options Directories• can specify more directories to search for header files

difference between (this is very important) #include <filename>

• only search in directories specified in options• mostly used for standard header files like iostream

#include "filename"• first search in the local directory, then the ones in options• for user defined header files


Adding Files to Projects in VC++ .cpp files that are compiled and linked together (like class

implementations) must be added to the project otherwise link error

Standard libraries are found and linked automatically no need to add anything to the project for these libraries

User-defined libraries, if available in object code (e.g. .lib files), must be added to the project otherwise link error

Header files may or may not be added in project if not added, they are shown as “external

dependencies” and this is OK No matter added to the project or not, the compiler still

needs to find the header files in a folder• they may not be found if directory settings are wrong, so

be careful!

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