Todays Agenda

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Todays Agenda

• Implementation Issues
• Modularity and Reuse
• Interfaces and Implementations (Review) ?
• Functions as Modules ?
• Use of Types (for Re-use)

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Types for Re-use 1

• Types classify (data) values
• So, each type is a set of values
• e.g. int m -2n-1 lt m lt 2n-1
• e.g. char c c is an ASCII value
• int and char are basic (primitive) types
• Arrays are structured (non-primitive) types

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Types for Re-use 2

• Users can define types
• Specify a (new) name
• Specify a set of values (by using other types)
• e.g. Celsius int
• e.g. WeeklyTemps Celsius7

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Types for Re-use 3

• C Syntax for user-defined types
• typedef int Celsius
• typedef Celsius WeeklyTemps7
• typdef int Matrix100100
• Matrix M ? Type declaration for Matrix type!
• Mi contains an int

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Types for Re-use 4

• Consider example Ordered Search
• / Pre-condition
• N is the size of A.
• A is sorted.
• Post-condition
• return P if AP x return 1
  otherwise.
• /
• extern int OrderedSearch(int x, int A, int N)
• // What if I wanted to search for a char. ?

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Types for Re-use 5

• Pre-conditions and Post-condition do not insist
  on int type.
• Algorithm for Binary Search do not require values
  to be of int type.
• Only the interface declaration and the function
  definition refer to int type.
• Even the implementation will work with
  appropriate comparisons ( and order)

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Types for Re-use 6

• Can we re-write the code?
• What is the ideal requirement?
• Any type should be acceptable as long there
• is an order function and an appropriate
  operation available.

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Types for Re-use 7

• Ideal Implementation
• / Pre-condition
• N is the size of A A is sorted
• Element type is orderable
• /
• extern int
• OrderedSearch(Element x, Element A, int N)

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Types for Re-use 8

• How do we obtain the ideal implementation?
• Define the specific type to be used
• / file element.h /
• typedef int Element
• Use the definition by including the header file
• / file OrderedSearch.h /
• include element.h

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Types for Re-use 9

• / file OrderedSearch.h /
• include element.h
• / Pre-condition
• N is the size of A A is sorted.
• Element type is orderable
• Post-condition
• return P if AP x return 1
  otherwise.
• /
• extern int
• OrderedSearch(Element x, Element A, int
  N)

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Types for Re-use 10

• / file order.h /
• include element.h
• / Check whether u and v are in order.
• Post-condition return 1 if u and v are in
  order
• 0
  otherwise
• /
• extern int ordered(Element u, Element v)

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Types for Re-use 11

• /file intOrderND.c /
• include element.h
• / Check whether (int)u and (int)v are in order
  /
• / Specialized Pre-condition
• u must be of type int
• v must be of type int
• /
• int ordered(Element u, Element v) return u lt v
  
• // Generate linkable gcc c intOrderND.c

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Types for Re-use 12

• / file bsearch.c /
• include order.h
• int OrderedSearch(Element x, Element A, int N)
• while (low lt high)
• else if (ordered(Amid, x))

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Types for Re-use 13

• Compile and Run
• Step1 Compile bsearch.c to create bsearch.o
• gcc c bsearch.c
• Step2 Create exectutable for bsearch application
• gcc o bsearchexe main.c bsearch.o
  intOrderND.o
• Step3 Execute the program
• ./bsearch_nd

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Personal Process for Programming

• Design ?
• Development
• Implementation Issues Modularity and Re-use
• Testing

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Modularity and Re-use (in C)

• Interfaces and Implementations
• Files in C
• Functions for Re-use
• Types for Re-use

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Types for Re-use (Review)

• User-defined Types in C
• Interfaces and User-defined Types
• Implementations and User-defined Types
• Re-use
• Disadvantage(s)

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Types for Re-use - Definition

• / file element.h /
• typedef int Element

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Types for Re-use - Interfaces

• / file osearch.h /
• include element.h

/ Pre-condition N is the size of A
A is sorted by an order defined on
Element. Post-condition
return P if AP x return 1 otherwise. /
extern int OrderedSearch(Element x,
Element A, int N)
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Types for Re-use - Interfaces

• / file order.h /
• include element.h

/ Check whether u and v are in order.
Post-condition return 1 if u and j are in
order 0
otherwise /
extern int ordered(Element u, Element v)
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Types for Re-use - Implementations

• / file bsearch.c /

include order.h int OrderedSearch(Element x,
Element A, int N)
while (low lt high) else if
(ordered(Amid, x))
// Generate linkable gcc c bsearch.c
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Types for Re-use - Implementations
/file intOrderND.c /
include element.h
/ Check whether (int)u and (int)v are in order
/ / Specialized Pre-condition u must be of
type int v must be of type int /
int ordered(Element u, Element v) return u lt v

// Generate linkable gcc c intOrderND.c
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Types for Re-use - Usage
/ file main.c /
include OrderedSearch.h
int main()
Element x Element A100 int N int pos
// read x, A and N.
pos OrderedSearch(x, A, N)
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Types for Re-use Usage

• int temp, j
• // read x
• scanf(d, temp) x (Element) temp

// read N scanf(d, N)
// read A for (j0 j lt N j)
scanf(d, temp) Aj (Element) temp
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Types for Re-use - Execution

• Compile
• gcc main.c bsearch.o intOrderND.o o bsnd
• Execute
• ./bsnd

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Types for Re-use - Re-definition

• / file element.h /
• typedef char Element

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Types for Re-use - Re-Implementation

• / file charOrderLex.c /
• int ordered(Element c, Element d)
• char i (char) c
• char j (char) d
• if (isalpha(i) isalpha(j))
• else if

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Types for Reuse - Reuse
char temp, j // read x scanf(c, temp) x
(Element) temp
// read N scanf(d, N)
// read A for (j0 j lt N j) scanf(
c, temp) Aj (Element) temp
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Types for Re-use - Execution

• Compile
• gcc main.c bsearch.o charOrderLex.o o bstc
• Execute
• ./bstc

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Types for Re-use - Disadvantages

• Need to use same .h file for types i.e.
  multiple copies of other files needed.
• Type conversions needed (from Element to char and
  vice-versa)
• Approach complex for non-primitive types
• (say string instead of int or char)