1. Announcements Midterm2 Grades to be announced NEXT Monday
Homework 5 Grades to be announced THIS WEEK
Homework 6 will be assigned this week

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 ( )
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 ) 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) similar to bool
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' 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 Examples
among built-in types like double, int, char, bool
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 Conversion from signed to unsigned integers
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
the bit sequence to represent –100 is the same as the one of

10. Type Casting Examples Conversion from int to char
int i = 72;
cout << char (i);
output is H
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:
...
default : }
- 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 is the value of selector, statements after default are executed

13. Switch statement (Section 7.3.2)
Restrictions
selector expression must be integer (char, boolean ok), cannot be real (double, float) or string
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 : invalid
Advantage
more efficient than if-else; only one statement is executed
Disadvantage
code becomes 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
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
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 #define identifier token Example
Another compiler directive
Generally written at the beginning of program (not in a function)
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 takes a translation unit as input and produces compiled object code as output
The object code is platform/architecture specific
The source code is 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 still 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. Next Arrays and vectors (Chapter 8)
including searching and sorting (partially Chapter 11)
Recursion, scope rules, global and static variables
partially Chapter 10