Announcements

1. Announcements • Homework 5 • Due this Thursday (December 4), 13:00 • Common Problems and Questions about HW5 • Monsters are not so intelligent • Just turn to a random direction and Move • If dies, dies and then resurrected • No loops until no wall • Be aware of the flow of the game • One of the monsters (the one that did not move in the previous iteration) and then player • Until the game is finished • Read the document and the email sent for all details • Do not use TurnRight in Random Turn member functions • Causes the monsters to move slowly • Instead Turn the robot to a random direction by updating the private data member directly or using Turn member function that you implemented for this HW in recitations • Number of things in the playground is not a constant value • In the grading process, we will use a different playground

2. Character Data Type (9.1) • is a built-in data type to represent a single character from the computer’s character set • most commonly used standard character set is ASCII • letters, digits, symbols, punctuation marks, control characters (e.g. end of line,end of file, etc.) • each character in ASCII set has a numeric code (0 .. 255) • See Table F.3 in page 763 for ASCII table • Character variables are defined using the type identifier char char a, ch, letter; • Character literals are represented within single quotes 'A''3''.''f' • Pay attention to the difference between strings with single letter and chars • "A" versus 'A' • first one is a string literal, second one is a character literal • String variables (objects) has several private data members even if it has a single character in it. However, char variables occupy just one byte.

3. Character Codes in ASCII set • Each character occupies one byte • that is why character codes are between 0 and 255 • first 32 characters (with codes 0 .. 31) are non-printable control characters • such as eof • blank character has the code 32 • Uppercase letters are consecutive and ordered in ASCII set • code for'A'is 65,'B'is 66,'C'is 67, …'Z'is 90 • Similarly, lowercase letters are also ordered and consecutive • code for'a'is 97, …'z'is 122 • Similarly digit characters are ordered and consecutive too • code for'0'is 48,'1'is 49, …'9'is 57 • Do not memorize the codes for letters and digits; you can do character arithmetic (see next slides)

4. Character Arithmetic • If you compare two characters (or a character with an integer) character codes are used in comparison • If you apply an arithmetic operator (+ - * / %) to a character, integer code of the character is processed • this is an implicit type casting (conversion) • And if you process the result of such an operation as character, a reverse conversion is automatically performed • you can also process the result as integer (actually this is the default behavior) • Example: the value of 'A'+ 2 is • 'C' if you process as a char (you do not have to know the codes in order to reach this result) • 67 if you process as integer or if you do not mean any type • Example: what is the value of 'Z'- 'A' ? • 25 (you do not have to know the codes of A and Z to answer this question)

5. Examples • Suppose digitch is a char variable and its content is a digit character (between '0' and '9'), how can you obtain that digit character’s numeric equivalent in an int variable digitnum? digitnum = digitch -'0'; • Write a function that takes a character parameter and returns the uppercase equivalent of it if parameter is a lowercase letter. If parameter is not a lowercase letter, function returns it unchanged. char toupper (char ch) { if (ch >= 'a' && ch <= 'z')//if lowercase return ch + ('A'-'a');//return its uppercase return ch;// otherwise return parameter unchanged }

6. Escape Sequences in C++ • Special symbols for some characters (mostly for control characters) to be used in character and string literals only. • Not to be used while entering input • Full list is in Table 4.1 (page 103) or Table A.5 (page 716) • Some escape sequences \n newline character \t tab (used for aligned output) \a bell \" double quote \'single quote \\ backslash • Example follows. What is the output? cout << "\"\\\n\"\"\n\\"; "\ "" \

7. Escape Sequences in C++ • If you want to represent a nonprintable character (such as new line, bell) in a string or character literal, you have to use nonprintable escape sequences. "bla bla \n bla" '\n' • However, for printable ones, you may use escape sequences whenever needed • You may or may not use escape sequence to represent a double quote character in a char literal • That means '\"'and'"'are the same • You may or may not use escape sequence to represent a single quote character in a string literal • That means "bla \' bla"and"bla ' bla"are the same • However, you have to represent a double quote in a string literal as an escape sequence. Similarly, you have to represent a single quote in a char literal as an escape sequence. • To represent a backslash, you always have to use escape sequence in both char and string literals

8. Type Casting • Conversion of an expression to another type • among built-in types like double, int, char • string cannot be used in type casting • syntax type_name (expression) • first expression is evaluated, then conversion is done • Examples cout << double (3) / 4; • output is 0.75 • first 3 is converted into double (3.0), then divided by 4 cout << 3 / 4; • without casting, integer division, output is 0 cout << double (3 / 4); • first 3 / 4 is evaluated to 0, then result is converted • output is 0

9. Type Casting Examples • real division using two integers int a, b; double div; ... div = double (a) / b; • Conversion from double to int cout << int (3.9); • double value is truncated • output is 3 • Conversion from signed to unsigned integers cout << unsigned int (-100); • output is NOT 100, output is 4294967196 • the bit sequence to represent –100 is the same as the one of 4294967196

10. Type Casting Examples • Conversion from int to char int i = 72; cout << char (i); • output isH • it is the character with code 72 • Complex example: what is the value of the following expression? 3 + double (62 * (int ('C') - int ('A'))) / 5 2 124 124.0 24.8 27.8

11. Cast operators in C++ • Four cast operators in C++, but only one is enough • static_cast <type_name> (expression) • functionally not different than type_name (expression) • Example cout << static_cast <double> (3) / 4; • output is 0.75 • Easier to spot casts in the code, but causes longer code

12. Switch statement (Section 7.3.2) • An alternative to if-else, but much less powerful • Useful when you have several choices • Syntax switch (selector_expression) { case label1: statement list; break; case label2: statement list; break; ... default : statement list; } • First selector is evaluated • labels are searched. If the value of selector is listed, then execution jumps there • all statements are executed until break • if no label bears the value of selector, statements after default are executed

13. Switch statement (Section 7.3.2) • Restrictions • selector expression must be integer, char or boolean, cannot be real (double, float) or string or something else • case labels must be given in literals (constant values) • no expressions case a*2: invalid • no ranges or lists case 1, 2, 3: invalid case 1 .. 10: invalid • Advantage • more efficient than if-else; only one statement is executed • Disadvantage • code may become hard to read • listing all possible values may not be convenient • Better to see in an example

14. Switch example • Input a digit between 0 and 9 and display its name. Display “not a digit” if not between 0 and 9. • See displaydigit.cpp • CAUTION: Do not forget break after each statement list, otherwise execution unconditionally continues until the next break or the end of the switch statement.

15. Three phases of creating an executable program • Sections from book: 7.2.2, 7.2.3, 7.2.4, 7.2.5 • 3 steps • preprocessing • compilation • linking

16. Preprocessing • The preprocessor processes all #include directives (and other preprocessor commands – all preprocessor commands start with #) • creates a translation unit which is the input of the next step (compilation) • all #include’d files are pasted in the translation unit recursively • e.g. replaces #include "foo.h" with contents of file foo.h, and does this recursively, for all #includes that foo.h includes and so on • exceptions • there are some preprocessor directives that causes conditional preprocessing #ifndef _FOO_H //if _FOO_H is not defined #define _FOO_H //define it and … header file for Foo goes here //include header file #endif • if _FOO_H is not defined, then it is defined and file is included, otherwise file is not included • Definitions are in a global symbol table • prevents multiple inclusion of the same header file in a program

17. Preprocessing • Where are the include files located? • You can ask the preprocessor to look in certain directories in order (Tools->Options->Directories...). E.g. You can add your directory after the system directories to be automatically searched for referenced include files • You get an error if the include file is not found in these directories • adding an include file to the project is not sufficient

18. Preprocessing • #defineidentifiertoken • Another compiler directive • Generally written at the beginning of program (not in a function) or in a header file • All instances of identifier in all functions are replaced with token during preprocessing • Token is any character sequence • Example #define LENGTH 10 ... cout << LENGTH << endl; • Displays 10 on screen • The above statement is compiled as cout << 10 << endl; • Because LENGTH is replaced with 10 before compilation (during preprocessing)

19. Compiler • The compiler has a translation unit as input and produces compiled object code as output • The object code is platform/architecture specific • the source code is (in theory at least) the same on all platforms • We may need to compile several cpp files • dice.cpp, randgen.cpp, prompt.cpp, robots.cpp, … • because some functions and class implementations are in those files • if you are using them in your program, you have to compile them together with your main cpp file • add to the same project • you may generate libraries out of those files • ready-to-use object code • need not to compile, but add the .lib file to the project

20. Linker • Linking combines object files and libraries to create a single executable program (the file with .exe extension) • May create errors even if compilation is successful • unresolved external symbol ... • undefined Symbol ... • Primary reason would be missing libraries or implementation files (like date.cpp, prompt.cpp) • header files provide the definition, but body is missing! • If you have such errors, try to find where those symbols are implemented and include those libs or cpps in your project

21. END of 2nd MIDTERM

22. Next • Structs (Section 7.4) • Arrays and vectors (Chapter 8) • including searching and sorting (partially Chapter 11) • Recursion, scope rules, global and static variables, function templates • partially Chapter 10 • Function templates are from Chapter 11 • Pointers and introduction to linked lists • partially Chapter 12