CS 1400 Feb 2007 Pick ups from chapters 2 and 3

Example; A person 15 years of age may acquire a driver’s lic. with permission from parents. A person over 15 is eligible without parental permission. A person under 15 is not eligible. Write a small program to input an age and output one of 3 messages: “permission required”, “eligible”, or “not eligible”.

Boolean constants A bool variable may only hold a bool value (true or false); bool flag; flag = true; flag = false; What would this do? while (true) {cout << “hello! “; }

Named constants Constants may be given symbolic names to represent them in a program; –Form: const type name = value; –Example: const float PI = ; const int SIZE = 24; –Alternative Form:#define name value #define PI #define SIZE 24 Defines should be place above main()

Character variables A variable of type char can hold one character; char sex; A character constant is delimited by single quotes; sex = ‘f’; if (sex == ‘m’) cout << “male”;

cin I/O rules Only digit characters (and sign) can be entered for an int variable. Only digit, decimal, and possibly E- notation characters (and sign) can be entered for a float variable. Only printable characters can be entered for a char variable.

char vs. literals A literal is different from a character! char c; cout << “hello world”; c = “hello world”;// ERROR! c = ‘h’;// CORRECT c = “h”;// ERROR!

Strings or char arrays A message or string of characters can be stored in a special array variable; char word[80]; // holds <80 characters cin >> word; cout << word << endl; Only printable characters can be input using cin (no blanks, tabs, etc.)

Initially limit use of string arrays… For now, only input and output will be done on arrays; word = “hello world”;// ERROR! if (word < “goodbye”)// ERROR! word1 = word2;// ERROR!

Combining assignments Multiple assignment statements may be combined –Example: a = b = c = 25; Shorthand notation for combining arithmetic operations and assignment –Example: a = a * 2;same asa *= 2; b = b – 5;same asb -= 5; c = c / 7;same asc /= 7;

Formatting output Requires: #include cout manipulators: setw(n) (set the minimum spaces for the next value output) setprecision(n) (set the precision or rounding for a float value) fixed (force output of float values in fixed-point notation) showpoint (show a decimal point with trailing zeros)

Controlling input Requires #include cin manipulators setw(n) do not input more than n-1 characters for the next variable textbook error, pg 128 char word[5]; cin >> setw(5) >> word;// user enters “Eureka” cout << word;// program outputs “Eure”

Special input examples… char sentence[20], ch; cin.getline(sentence, 20); –reads all characters on a line (up to 19 in count) from the keyboard and stores them in array sentence cin.get(ch); –reads the next input character (including white spaces) cin >> ch; –reads the next printable character (ignoring white spaces) cin.ignore (); –ignore (discard) the next input buffer character

More math library functions… Requires: #include functionsexamples absy = abs(x); sqrty = sqrt(a*a + b*b); logy = log(x); siny = sin(x+z); cosy = cos(x); tany = tan(x); etc…

File Output Requires:#include ofstream fout; fout.open (“report.txt”); fout << “hello from a file!\n”; fout.close(); To write to report.txt on the a: drive; fout.open (“a:\\report.txt”); fout.open (“a:report.txt”); fout.open (“a:\report.txt”); // ERROR!

File Input Requires:#include int a, b; ifstream fin; fin.open (“report.txt”); fin >> a >> b; cout << “sum is: “ << a+b << endl; fin.close();

Example… Write a program to generate a weekly report of concert hall business for a touring show. –assume:reserved seat tickets$80 stadium seat tickets$50 standing tickets$35 production company gets 80%

Input file… line 1:tour name line 2 reserved stadium standing Example: Rolling Stones Geriatric Tour a:tour.txt