CS 1400

1
CS 1400

• Feb 2007
• Pick ups from chapters 2 and 3

2
Example

• A person 15 years of age may acquire a drivers
  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.

3
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 ltlt hello!

4
Named constants

• Constants may be given symbolic names to
  represent them in a program
• Form const type name value
• Example
• const float PI 3.14159
• const int SIZE 24
• Alternative Form define name value
• define PI 3.14159
• define SIZE 24
• Defines should be place above main()

5
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 ltlt male

6
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.

7
char vs. literals

• A literal is different from a character!
• char c
• cout ltlt hello world
• c hello world // ERROR!
• c h // CORRECT
• c h // ERROR!

8
Strings or char arrays

• A message or string of characters can be stored
  in a special array variable
• char word80 // holds lt80 characters
• cin gtgt word
• cout ltlt word ltlt endl
• Only printable characters can be input using cin
  (no blanks, tabs, etc.)

9
Initially limit use of string arrays

• For now, only input and output will be done on
  arrays
• word hello world // ERROR!
• if (word lt goodbye) // ERROR!
• word1 word2 // ERROR!

10
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 as a 2
• b b 5 same as b - 5
• c c / 7 same as c / 7

11
Formatting output

• Requires include ltiomanipgt
• 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)

12
Controlling input

• Requires include ltiomanipgt
• cin manipulators
• setw(n)
• do not input more than n-1 characters for the
  next variable
• textbook error, pg 128
• char word5
• cin gtgt setw(5) gtgt word // user enters Eureka
• cout ltlt word // program outputs Eure

13
Special input examples

• char sentence20, 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 gtgt ch
• reads the next printable character (ignoring
  white spaces)
• cin.ignore ()
• ignore (discard) the next input buffer character

14
More math library functions

• Requires include ltcmathgt
• functions examples
• abs y abs(x)
• sqrt y sqrt(aa bb)
• log y log(x)
• sin y sin(xz)
• cos y cos(x)
• tan y tan(x)
• etc

15
File Output

• Requires include ltfstreamgt
• ofstream fout
• fout.open (report.txt)
• fout ltlt hello from a file!\n
• fout.close()
• To write to report.txt on the a drive
• fout.open (a\\report.txt)
• fout.open (areport.txt)
• fout.open (a\report.txt) // ERROR!

16
File Input

• Requires include ltfstreamgt
• int a, b
• ifstream fin
• fin.open (report.txt)
• fin gtgt a gtgt b
• cout ltlt sum is ltlt ab ltlt endl
• fin.close()

17
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

18
Input file

• line 1 tour name
• line 2 reserved stadium standing
• Example

• Rolling Stones Geriatric Tour
• 7500 4110

atour.txt