1
CS 112 Introduction to
Programming
Lecture #15:
Decomposition and
the Calendar Program
http://flint.cs.yale.edu/cs112/
2
Outline
rAdmin. and review
rStepwise refinement using the Calendar
program as an example
3
Recap: Variable Scope and Duration
rScope
mA local variable is accessible after it is declared
and before the end of the block
mA class variable is accessible in the whole class
mParameter passing with ref and out makes
some variables aliases of others
rDuration
mA 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.
4
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 < 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 > 0) return temp;
}
// now only x and NoOfTries in scope
return 0;
} // AskForPositiveNumber
static void Main( string[] args )
{…}
}
5
Stepwise Refinement
rmain idea: use methods to divide a large
programming problem into smaller pieces that are
individually easy to understand ------- decomposition
rstepwise refinement (or top-down design)
mstart with the main program
mthink about the problem as a whole and identify the major
pieces of the entire task
mwork each of these big pieces one by one
mfor each piece, think what is its major sub-pieces, and repeat
this process
rrun the calendar example
6
Calendar: Requirements
rGet a year from the user, the earliest year should be
1900
rGet a month from the user, the input should be from
0 to 12
mIf 0, print calendar for all 12 months
mOtherwise, print the calendar of the month of the year
rEach month is displayed as: 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
