Wednesday, 10/23/02, Slide #1 CS 106 Intro to CS 1 Wednesday, 10/23/02  QUESTIONS??  Today:  Discussion of HW #3  The const modifier for functions and parameters  The char object type  Some new numeric operators  Reading: pp of Chapter 6  Exercises: p. 150 #9, 10, 19

Wednesday, 10/23/02, Slide #2 Using the const modifier on member functions  If a member function does not change the invoking object, we can prevent accidental change by adding the const modifier (Recall: Standing for “Constant”):  Complex Complex::AddC (Complex x)  Function code permitted to change invoking object  Complex Complex::AddC (Complex x) const  Function code not permitted to change invoking object  Which Complex member functions should be const? Constructor? InputC()? OutputC()? AddC()? SubC()? MultC()?

Wednesday, 10/23/02, Slide #3 Using the const modifier on parameters  We use reference parameters if we do want to change the argument -- the actual argument is used  We use value parameters if we don’t want to change the argument -- a copy of the argument is used  If parameters are class objects, sometimes copies can be big -- we want to use the actual object, but not change it  Const reference parameters let us use the actual object, but don’t let us change it: Complex Complex::AddC (Complex x) const //uses a copy of x Complex Complex::AddC (Complex& x) const //uses x, can change x Complex Complex::AddC (const Complex& x) const //uses x, can’t // change x

Wednesday, 10/23/02, Slide #4 Type char objects  char is a built-in (“primitive”) object type, like int, float, double  char declaration: char ch; or char c1(‘%’); or char c2 = ‘x’;  char constants: single characters enclosed in single quotes  Operators that can be used with type char:  Extract: >>, Insert: >, Insert: <<  Extraction operator ignores whitespace -- uses it to separate one (non-whitespace) char from the next.  Assign: =, Comparisons: ==, !=, >, =,, =, <=  Comparisons are based on the order of characters in terms of their ASCII codes

Wednesday, 10/23/02, Slide #5 Changing types (in general)  There are two main ways to change objects from one type to another:  Assign the object to a variable of the new type:  int num = 3.14 (what value does num have?)  char letter = “Hi Mom” (what’s letter now?)  Use “Typecasting” – type acts as a function:  int(3.14) ? int(‘b’) ? char(126) ? double(10) ?

Wednesday, 10/23/02, Slide #6 char library functions  Since char is a primitive type (not a class type), we don’t use the ‘dot’ notation (unless the function has a char parameter, but is a member of some other class)  Some functions that return true/false (bool) values (I’ve given prototypes to show return and parameter types):  bool islower (char c);  bool isupper (char c);  bool isalpha (char c);  bool isdigit (char c);  bool isalnum (char c);  bool isspace (char c);  bool ispunct (char c);  bool isprint (char c);

Wednesday, 10/23/02, Slide #7 The library: for changing to uppercase, lowercase  contains the following two functions:  int tolower(char c);  int toupper(char c);  Returns the ASCII code of c changed to lower/upper case  To get type char, either assign to char object or use char() typecasting Program segment: char c1 = 'a', c2 = 'B'; cout << c1 << c2 << endl; cout << toupper(c1) << tolower(c2) << endl; char c3 = toupper(c1); cout << c3 << char(tolower(c2)) << endl; Output: aB 6598 Ab

Wednesday, 10/23/02, Slide #8 More int operators: Mod operator %  Produces the remainder of the integer division  Examples 5 % 2 evaluates to 1 12 % 4 evaluates to 0 4 % 5 evaluates to 4  % has same precedence as * and /

Wednesday, 10/23/02, Slide #9 Increment and Decrement Operators ++ and --  Increment and Decrement (prefix and postfix):  ++x, x++ : increase value of x by 1  --x, x-- : decrease value of x by 1  Examples:  ++count;  turnsLeft--;

Wednesday, 10/23/02, Slide #10 Other operators: Compound Assignment  x += y; Replaces x with x + y  x -= y; Replaces x with x - y  Examples:  Balance += Deposit;  TimeLeft -= TimeOfTurn;