Dale Roberts, Lecturer

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Department of Computer and Information
Science,School of Science, IUPUI
CSCI 230
Structures Functions and Arrays

• Dale Roberts, Lecturer
• Computer Science, IUPUI
• E-mail droberts_at_cs.iupui.edu

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Using Structures With Functions

• Passing structures to functions
• Pass entire structure or pass individual members
• Both pass call by value
• It is not a good idea to pass a structure to or
  return from function.The better way is passing a
  pointer to the structure to the functions and
  returning a pointer from function.
• To pass structures call-by-reference
• Pass its address
• Pass reference to it
• To pass arrays call-by-value
• Create a structure with the array as a member
• Pass the structure

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Using Structures With Functions (cont.)

• Example
• day_of_year(struct date pd)
• int i, day, leap
• day pd -gt day
• leap pd-gtyear4 0 pd-gtyear 100 0
  pd-gtyear400 0
• for (i1 i lt pd -gt month i)
• day day_tableapi
• return (day)
• The declaration struct date pd
• says that pd is a pointer to a structure of the
  type date
• If p is a pointer to a structure, then p-gt
  member_of_structure refers to the particular
  members, like pd -gt year
• p-gt member_of_structure is equivalent to
  (p).member_of_structure
• Notice . has higher precedence than
  pd.year is wrong, since pd.year is not a
  pointer.
• Both -gt and . associate from left to right. So
  p -gt q -gt member
• are (p-gtq)-gtmember.
• Example emp.birthday.month are
  (emp.birthday).month

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Using Structures With Functions (cont.)

• -gt and . both are at the highest precedence
  (together with () for function and for array
  subscripts)
• Example
• struct
• int x
• int y
• p
• p-gtx is equivalent to (p-gtx) / increment
  x, not p /
• (p)-gtx / increment p before access x /
• p-gty / fetch whatever y points to /
• p-gty / increments y after accessing
  whatever y point to /
• (p-gty) / increments whatever y point to,
  just like p-gty /
• p-gty / increments p after accessing
  whatever y point to /

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typedef

• typedef
• Creates synonyms (aliases) for previously defined
  data types
• Use typedef to create shorter type names
• Example
• typedef struct card CardPtr
• Defines a new type name CardPtr as a synonym for
  type struct card
• typedef does not create a new data type while it
  only creates an alias
• Example

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Array of Structures

• Example (before)
• char namePERSONNAMESIZE
• int tscorePERSON
• int mathPERSON
• int englishPERSON
• Initialization of structure array
• struct person_data
• .. .. .. ..
• person
• Jane,180,89,91,
• John,190,90,100,
• .. .. .. ..
• / similar to 2D array /
• Example using separated arrays
• average (int tscore, int math, int eng, int n)

struct person_data char nameNAMESIZE int
tscore int math int english personPERSON
(now) ?
the inner brace is not necessary Jane,180,89,91
, John,190,90,100, .. .. .. ..
?
Example using pointer to structure average
(struct person_data person, int n) int i,
total0,mathtotal 0, engtotal0 for (i0 iltn,
i) total person-gttscore mathtotal
person-gtmath engtotal person-gteng person
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Unions

• union
• Memory that contains a variety of objects over
  time
• Only contains one data member at a time
• Members of a union share space
• Conserves storage
• Only the last data member defined can be accessed
• union declarations
• Same as struct
• union Number
• int x
• float y
• union Number value
• Valid union operations
• Assignment to union of same type
• Taking address
• Accessing union members .
• Accessing members using pointers -gt

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Define union
Initialize variables Set variables Print
Program Output
Put a value in the integer member and print both
members. int 100 double -925595921174331360000
00000000000000000000000000000000000000000.00000  
Put a value in the floating member and print both
members. int 0 double 100.000000
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Bit Fields

• Bit field
• Member of a structure whose size (in bits) has
  been specified
• Enable better memory utilization
• Must be declared as int or unsigned
• Cannot access individual bits
• Declaring bit fields
• Follow unsigned or int member with a colon ()
  and an integer constant representing the width of
  the field
• Example
• struct BitCard
• unsigned face 4
• unsigned suit 2
• unsigned color 1
• Unnamed bit field
• Field used as padding in the structure
• Nothing may be stored in the bits
• Unnamed bit field with zero width aligns next bit
  field to a new storage unit boundary

struct Example unsigned a 13 unsigned
3 unsigned b 4
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Enumeration Constants

• Enumeration
• Set of integer constants represented by
  identifiers
• Enumeration constants are like symbolic constants
  whose values are automatically set
• Values start at 0 and are incremented by 1
• Values can be set explicitly with
• Need unique constant names
• Example
• enum Months JAN 1, FEB, MAR, APR, MAY,
  JUN, JUL, AUG, SEP, OCT, NOV, DEC
• Creates a new type enum Months in which the
  identifiers are set to the integers 1 to 12
• Enumeration variables can only assume their
  enumeration constant values (not the integer
  representations)

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1 January 2 February 3 March 4
April 5 May 6 June 7 July
8 August 9 September 10 October 11
November 12 December
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Storage Management

• C supports 4 functions, malloc(),
  calloc(),free(), and cfree() for storage
  management
• malloc(n)
• allocate a node while its content is still
  garbage
• n is an integer, indicating the size of memory in
  byte which you would like to allocate
• malloc() return a character pointer to that
  memory
• So, you have to use cast operator (type), to
  change the type of the pointer.
• Example
• int ip
• ip (int) malloc(sizeof(int))
• struct treeNode tp
• tp (struct tnode ) malloc(sizeof(struct
  tnode))

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Storage Management (cont.)

• free(p)
• free() will release the memory allocated by
  malloc().
• p is the pointer containing the address
  returning from malloc().
• Example
• int ip
• ip (int) malloc(sizeof(int))
• ... .. ..
• free(ip) / Question can you free(ip) after
  ip ? /
• Example
• struct treeNode tp
• tp(struct treeNode )malloc(sizeof(struct
  treeNode ))
• ... .. ..
• free(tp)
• When there is no further memory, malloc() will
  return NULL pointer. It is a good idea to check
  the returning value of malloc().
• if ((ip(int )malloc(sizeof(int))) NULL)
• printf(\nMemory is FULL\n)
• exit(1)

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Storage Management (cont.)

• calloc(n,size)
• calloc() allow you to allocate an n elements
  array of same data type. Because n can be an
  integer variable, you can use calloc() to
  allocate a dynamic size array.
• n is the element number of array that you want
  to allocate.
• size is the number of byte of each element.
• Unlike malloc(), calloc() guarantees that memory
  contents are all zero
• Example allocate an array of 10 elements
• int ip
• ip (int) calloc(10, sizeof(int))
• (ip1) refer to the 2nd element, the same as
  ip1
• (ipi) refer to the i1th element, the same
  as ipi
• Like malloc(), calloc() will return NULL, if no
  further memory is available.
• cfree(p)
• cfree() releases the memory allocated by
  calloc().
• Example
• cfree(ip)