Derived Types

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Chapter 12
Derived Types-- Enumerated, Structure and Union
These slides are intended for students at IUPUI
who are users of the book B.A. Forouzan, R.F.
Gilberg, Computer Science A Structured Approach
Using C, Brooks/Cole, second edition, 2001, ISBN
0-534-37482-4. Additions have been made to
existing slides from Brooks/Cole and some new
slides have been added by Kris A. Dines, Ph.D.,
Indiana University-Purdue University (IUPUI)
(kdines_at_iupui.edu) for a C course in Electrical
Engineering. Please see Brooks/Cole website
(www.brookscole.com) to download original slides.
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Derived Types

• Those made from existing types.
• Arrays are collections of existing types
• int array11,2,3
• Pointers are address locations of existing types
• float x
• float pxx
• Can also define our own groups of variables and
  give that group a name. (structs)

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Figure 12-1 Derived types available in C
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Figure 12-2 Type definition using typedef
typedef int Int32 // Integer of specific
size (32-bit machine) Int32 ivalue
// New type used as any other Int32
pValueivalue
Identifier (better)
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More typedef Examples

• String type
• typedef char String
• Use it String myString156
• Pointer type
• typedef int pInt
• int a
• pInt pa

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Figure 12-3 Enumerated type discrete set of
values with names
for only one variable
tag creates a type to use for defining many
variables
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Figure 12-4 Enumerated type set of constants
Symbolic names rather than integers red0,
white1,,, yellow4 (constants)
With tag enum color color0red
With typedef COLORS color0red
Use anywhere integers are used
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Reassigning Constant Integer Values of enum
Symbols

• Set to unique, but arbitrary integers
• enum TV fox11, abc5, cnn66
• Start at one and increment by one
• enum months Jan1,Feb, Mar, Apr,,, etc.

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Enumerated Type Example

• enum TV fox11, abc5, cnn66 // define it
• int main()
• enum TV myChannelcnn // TV variable is
  myChannel
• if(myChannelfox)
  // Test for fox
• printf(I am watching the world series\n)
• else
• printf(I am not watching the world series\n)

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12-3 Structures

• structure collection of related data elements
• various types
• represents some mathematical or problem domain
  object.
• field a data element in the structure

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Structures Representing Fractions

• struct fraction // a tagged structure
• // can reuse for many variables
• int numerator
• int denominator
• struct fraction frac1 // declare a fraction
  variable
• struct // structure variable declaration
• // just defines frac1 variable...cannot
  reuse
• int numerator
• int denominator
• frac1 // just defines frac1... would have
  to
• //
  repeat for frac2, etc. ? useless

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Structures Representing Fractions (Contd.)

• struct fraction // a tagged structure
• // can reuse for many variables
• int numerator // (put in a header file)
• int denominator
• int main()
• struct fraction frac1 // Accessing fields
• frac1.numerator3 // 3/4
• frac1.denominator4
• //...

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typedefd Structure

• Recall
• typedef int Int32
• typedef struct fraction
• int numerator
• int denominator
• Fraction // new type

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Typedef Structures Representing Fractions
(Contd.)

• typedef struct fraction // a typedefd structure
• // can reuse for many variables
• int numerator // (put in a header file)
• int denominator
• Fraction
• int main()
• Fraction frac1 // Accessing fields
• frac1.numerator3 // 3/4
• frac1.denominator4
• //...

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Typedef Structures Representing Fractions
(Contd.) Use these

• typedef struct fraction // a typedefd structure
• // can reuse for many variables
• int numerator // (put in a header file)
• int denominator
• Fraction // traditional format
• typedef struct int numerator int
  denominator Fraction // equivalent
• OR
• typedef struct / can leave off tag if
  typedefd/
• int numerator
• int denominator
• Fraction

Existing type
New type
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Figure 12-5
FILE fp // Pointer to a FILE structure
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Figure 12-10 struct format variations
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Figure 12-11 Initializing structures
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12-4 ACCESSING FIELDS IN STRUCTURES

• Each field is just a variable usable as such
• Fraction frac13,4 // the fraction ¾
• frac1.numerator3 // same as above...
• frac1.denominator4

dot is the member operator that digs into a
structure to get a variable then use it like any
other variable
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Multiply Fractions

• typedef struct
• int numerator
• int denominator FRACTION
• int main (void)
• /Local Definitions /
• FRACTION fr1
• FRACTION fr2
• FRACTION res
• / Statements read two fractions /
• printf("Write the first fraction in the form of
  x/y ")
• scanf ("d /d", fr1.numerator,
• 
  fr1.denominator)
• // contd........

• // main() contd.........
• printf("Write second fraction in the form of
  x/y ")
• scanf ("d /d", fr2.numerator,
• 
  fr2.denominator)
• // the actual multiply
• res.numerator fr1.numerator
  fr2.numerator
• res.denominator fr1.denominator
  fr2.denominator
• printf("\nThe result of d/d d/d is d/d",
  
• fr1.numerator, fr1.denominator,
• fr2.numerator, fr2.denominator,
• res.numerator, res.denominator)
• return 0

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Operations on Structures

• Assignment or copy is the only one except for
  those you program yourself.
• Fraction frac13,4 // 3/4
• Fraction frac21,2 // 1/2
• frac2frac1 // now frac2 holds 3/4

// element-by-element copy
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Figure 12-13
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Figure 12-14 Pointers to structures
ptr.x is WRONG dot takes precedence (ptr)
goes to where the structure lives
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Pointer Selection Operator( p-gtmember )

• Fraction frac13,4 //a Fraction initialized
• Fraction pFrac1 // pointer to a Fraction
• pFrac1frac1 // pointer has value
  addressof(frac1)
• // Equivalent ways to access member fields
• frac1.numerator17 // dot member operator
• (pFrac1).numerator17 // deref pointer then dot
  into it
• pFrac1-gtnumerator17 // selection
  operator (preferred)
• // e.g., mul numerators
• pFrac3-gtnumerator (pFrac1-gtnumerator)
  (pFrac2-gtnumerator)

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LECTURE 9 END