CS 112 Introduction to Programming

1
CS 112 Introduction to Programming

• Lecture 14
• The Calendar Program
• Http//zoo.cs.yale.edu/classes/cs112/

2
Outline

• Admin. and review
• Stepwise refinement using the Calendar program as
  an example

3
Admin.

• Assignment 2 office hours
• 1200 PM - 500 PM (DL 120)
• 0230 PM 400 PM (AKW 202)
• 0500 PM 630PM (DL 120)

4
Recap Variable Scope and Duration

• Scope
• A local variable is accessible after it is
  declared and before the end of the block
• A class variable is accessible in the whole class
• Parameter passing with ref and out makes some
  variables aliases of others
• Duration
• A local variable may exist but is not accessible
  in a method,
• e.g., method A calls method B, then the local
  variables in method A exist but are not
  accessible in B.

5
Example
class Test const int NoOfTries 3 //
class scope static int Square ( int x ) //
formal arg. // NoOfTries and x in
scope int square x x // square local
var. // NoOfTries, x and square in scope
return square static int
AskForAPositiveNumber ( int x ) //
NoOfTries and x in scope for ( int i 0
i lt NoOfTries i ) // NoOfTries, i,
and x in scope string str
Console.ReadLine() // NoOfTries, i, x,
and str in scope int temp
Int32.Parse( str ) // NoOfTries, i, x,
str and temp in scope if (temp gt 0)
return temp // now only x and
NoOfTries in scope return 0 //
AskForPositiveNumber static void Main(
string args )
6
Review Program Development Process
7
Calendar Requirements

• Get a year from the user, the earliest year
  should be 1900
• Get a month from the user, the input should be
  from 0 to 12
• If 0, print calendar for all 12 months
• Otherwise, print the calendar of the month of the
  year

8
Design
year GetYearFromUser()
month GetMonthFromUser()
month ? 0
t
f
PrintMonth(month, year)
PrintYear(year)
9
PrintMonth( month, year )

• January 1900
• Sun Mon Tue Wed Thu Fri Sat
• 1 2 3 4 5 6
• 7 8 9 10 11 12 13
• 14 15 16 17 18 19 20
• 21 22 23 24 25 26 27
• 28 29 30 31

10
Design PrintMonth( month, year )
Print month header
GetFirstWeekday(month, year)
IndentInitialWeekdays
GetMonthDays(month, year)
Print each day
11
Design PrintMonth( month, year )
Print month header
GetFirstWeekday (month, year)
IndentInitialWeekdays
GetMonthDays(month, year)
Print each day
12
Implementation

• Important
• Implement simple methods first
• Test a method
• using some dummy method calls, or
• e.g, Call the method in Main() with some typical
  test cases
• using Visual Studio Immediate window

13
Methods To Be Implemented and an Order to
Implement them

• static string GetMonthName( int month )
• // The English word for a specific month
• static bool IsLeapYear( int month, int year )
• // Check if a year is a leap year
• static int GetMonthDays( int month, int year )
• // Calculate the number of days for a specific
  month of a specific year
• static int GetFirstWeekday( int month, int year
  )
• // Calculate the weekday of the 1 days of a
  month (in a specific year)
• static void IndentInitialWeekdays( int weekday )
• // Indenting the first line so that the
  first day appears in the correct position
• static void PrintMonth( int month, int year )
• static void PrintYear( int month, int year )
• static void GievInstructions( int month, int year
  )
• static void GieYearFromuser( int month, int year
  )
• static void GetMonthFromUser( int month, int year
  )
• static void Main( string args )

14
Example Implementing GetMonthName

• static string GetMonthName(int month)
• switch (month)
• case 1 return ("January")
• case 2 return ("February")
• case 3 return ("March")
• case 4 return ("April")
• case 5 return ("May")
• case 6 return ("June")
• case 7 return ("July")
• case 8 return ("August")
• case 9 return ("September")
• case 10 return ("October")
• case 11 return ("November")
• case 12 return ("December")
• default return ("Illegal month")
• // end of method GetMonthName

static void Main( string args )
Console.WriteLine( GetMonthName( 1 ) ) //
end of method Main
Test
15
Example Implementing IsLeapYear

• static bool IsLeapYear(int year)
• return ( (year 4 0) (year 100 ! 0)
  )
• ( year 400 0)
• // end of method IsLeapYear

static void Main( string args )
Console.WriteLine( IsLeapYear( 2000 ) )
Console.WriteLine( IsLeapYear( 1900 ) )
Console.WriteLine( IsLeapYear( 2003 ) ) // end
of method Main
16
Example Implementing GetMonthDays

• static int GetMonthDays(int month, int year)
• switch ( month )
• case 2
• if ( IsLeapYear( year ) )
• return ( 29 )
• else
• return ( 28 )
• case 4 case 6 case 9 case 11
• return ( 30 )
• default
• return ( 31 )
• // end of switch
• // end of method GetMonthDays

static void Main( string args )
Console.WriteLine( GetMonthDays( 2, 2000 ) )
Console.WriteLine( GetMonthDays( 2, 1900 ) )
Console.WriteLine( GetMonthDays( 6, 2003 )
) // end of method Main