User_defined Structure Type

1
User_defined Structure Type

• Database, record and structure
• A structure type is a data type for a
• record composed of multiple components
• For example a database of planets needs
• Name Jupiter
• Diameter 142,980 km
• Moons 16
• Orbit time 11.9 yr
• Rotation time 9.925 hr

2
User_defined Structure Type

• We need to use define a structure type
• define STRSIZE 10
• typedef struct
• char nameSTRSIZE
• double diameter
• int moons
• double orbit_time,
• rotation_time
• planet_t suffix _t is used to show it is a
  type

3
User_defined Structure Type

• Also we need to define structure variables of the
  defined structure type
• planet_t previous_planet, current_planet
• blank_planet , 0, 0, 0, 0
• In the program we use variables of the structure
  type
• current_planet blank_planet

4
User_defined Structure Type

• Also we can define the a structure containing
  components that are structure. Such an structure
  is referred to as hierarchical structure
• For example
• typedef struct
• double diameter
• planet_t planets9
• char galaxySTRSIZE
• solar_sys_t

5
Manipulating Individual Components of a Structure
Data Object

• Direct component selection (.) can be used to
  reference a component of a structure. For
  example
• strcpy(current_planet.name, Jupiter)
• current_planet.diameter 142980
• current_planet.moon16
• current_planet.orbit_time11.9
• current_planet.rotation_time9.925

6
Operators Precedence

• aj, f(), left
  highest
• , -- (postfix) left
• , --, !(prefix) right
• -, , (unary) , right
• (type name) right
• , /, left
• , - left
• lt, gt, lt, gt left
• , ! left
• left
• left
• , , -, , /, right
  lowest

7
Structure Type Data as Input and Output
Parameters

• We can assign one structure to another structure
  variable, however we can not apply the equality
  and inequality operators to a structure type as a
  unit.
• When a structure variable is passed to a
  function, if it is input its value is copied to
  the formal variable and if it is output we must
  apply the address of operator to pass it as a
  pointer to the variable.

8
Function with a Structured Input Variable

• /
• Displays with labels all components of a
  planet_t structure
• /
• void
• print_planet(planet_t pl) / input - one planet
  structure /
• printf("s\n", pl.name)
• printf(" Equatorial diameter .0f km\n",
  pl.diameter)
• printf(" Number of moons d\n",
  pl.moons)
• printf(" Time to complete one orbit of the
  sun .2f years\n",
• pl.orbit_time)
• printf(" Time to complete one rotation on
  axis .4f hours\n",
• pl.rotation_time)

9
Function Comparing Two Structured Values for
Equality

• include ltstring.hgt
• /
• Determines whether or not the components of
  planet_1 and planet_2 match
• /
• int
• planet_equal(planet_t planet_1, / input -
  planets to /
• planet_t planet_2) /
  compare /
• return (strcmp(planet_1.name,
  planet_2.name) 0
• planet_1.diameter
  planet_2.diameter
• planet_1.moons planet_2.moons
  
• planet_1.orbit_time
  planet_2.orbit_time
• planet_1.rotation_time
  planet_2.rotation_time)

10
Function with a Structured Output Argument

• /
• Fills a type planet_t structure with input
  data. Integer returned as
• function result is success/failure/EOF
  indicator.
• 1 gt successful input of one planet
• 0 gt error encountered
• EOF gt insufficient data before end of
  file
• In case of error or EOF, value of type
  planet_t output argument is
• undefined.
• /

11

• int
• scan_planet(planet_t plnp) / output - address
  of planet_t structure
• 
  to fill /
• int result
• result scanf("slfdlflf",
  (plnp).name,
• 
  (plnp).diameter,
• 
  (plnp).moons,
• 
  (plnp).orbit_time,
• 
  (plnp).rotation_time)
• if (result 5)
• result 1
• else if (result ! EOF)
• result 0
• return (result)

12
Indirect Component Selection Operator

• In the indirect referencing (pnlp).moons
  parenthesizing was used to override the default
  operator precedence
• C provide a single operator that cobines
  indirection and component selection operator.
• (structp). component is equal to
• strucpt -gt component

13

• int
• scan_planet(planet_t plnp) / output - address
  of planet_t structure
• 
  to fill /
• int result
• result scanf("slfdlflf",
  plnp-gtname,
• (plnp-gtdiameter),
• (plnp-gtmoons),
• (plnp-gtorbit_time),
• (plnp-gtrotation_time))
• if (result 5)
• result 1
• else if (result ! EOF)
• result 0
• return (result)

14
Function get_planet Returning a Structured Result
Type

• /
• Gets and returns a planet_t structure
• /
• planet_t
• get_planet(void)
• planet_t planet
• scanf("slfdlflf", planet.name,
• planet.diameter,
• planet.moons,
• planet.orbit_time,
• planet.rotation_tim
  e)
• return (planet)
• current_planet get_planet() is same as
  scan_planet(current_planet)

15
A Function with Structure Result

• Suppose we defined the following structure for
  time
• typedef struct
• int hour, minute, seconds
• time_t
• And in the program time_now defined as a
  variable of type time_t
• If time_now initialized by 215832 and secs
  initialized by 97 we want by calling
• time_now new_time(time_now,secs)
• time_now becomes 220009

16

• Function to Compute an Updated Time Value
• /
• Computes a new time represented as a time_t
  structure
• and based on time of day and elapsed seconds.
• /
• time_t
• new_time(time_t time_of_day, / input - time to
  be updated /
• int elapsed_secs) / input - seconds
  since last update /
• int new_hr, new_min, new_sec
• new_sec time_of_day.second
  elapsed_secs
• time_of_day.second new_sec 60
• new_min time_of_day.minute new_sec /
  60
• time_of_day.minute new_min 60
• new_hr time_of_day.hour new_min / 60
• time_of_day.hour new_hr 24
• return (time_of_day)

17
Abstract Data Type

• A user-defined data type combined with a set of
  basic operations.
• For example
• data type planet_t
• operations scan_planet, print_planet,
  planet_equal
• data type complex_t (complex number abi)
• operations scan, print, add, subtract,
  multiply, divide, abs

18
A User_Defined Type for Complex Numbers

• Partial Implementation of Type and Operators for
  Complex Numbers
• /
• Operators to process complex numbers
• /
• include ltstdio.hgt
• include ltmath.hgt
• / User-defined complex number type /
• typedef struct
• double real, imag
• complex_t
• int scan_complex(complex_t c)
• void print_complex(complex_t c)
• complex_t add_complex(complex_t c1, complex_t
  c2)
• complex_t subtract_complex(complex_t c1,
  complex_t c2)
• complex_t multiply_complex(complex_t c1,
  complex_t c2)
• complex_t divide_complex(complex_t c1, complex_t
  c2)
• complex_t abs_complex(complex_t c)

19

• / Driver
  /
• int
• main(void)
• complex_t com1, com2
• / Gets two complex numbers /
• printf("Enter the real and imaginary parts
  of a complex number\n")
• printf("separated by a spacegt ")
• scan_complex(com1)
• printf("Enter a second complex numbergt ")
• scan_complex(com2)
• / Forms and displays the sum /
• printf("\n")
• print_complex(com1)
• printf(" ")
• print_complex(com2)
• printf(" ")
• print_complex(add_complex(com1, com2))

20

• / Forms and displays the difference /
• printf("\n\n")
• print_complex(com1)
• printf(" - ")
• print_complex(com2)
• printf(" ")
• print_complex(subtract_complex(com1,
  com2))
• / Forms and displays the absolute value
  of the first number /
• printf("\n\n")
• print_complex(com1)
• printf(" ")
• print_complex(abs_complex(com1))
• printf("\n")
• return (0)

21

• / Returns sum of complex values c1 and c2/
• complex_t
• add_complex(complex_t c1, complex_t c2) / input
  - values to add /
• complex_t csum
• csum.real c1.real c2.real
• csum.imag c1.imag c2.imag
• return (csum)
• /Returns difference c1 c /
• complex_t
• subtract_complex(complex_t c1, complex_t c2) /
  input parameters /
• complex_t cdiff
• cdiff.real c1.real - c2.real
• cdiff.imag c1.imag - c2.imag
• return (cdiff)

22
Parallel Arrays And Arrays of Structures

• To represent student information we used parallel
  arrays
• int id50
• double gpa50
• Instead of using parallel arrays to represent the
  student information
• an array of structure can be used
• typedef struct
• int id
• double gpa
• student_t
• student_t stu_listMAX_STU

23
Parallel Arrays And Arrays of Structures

• If function scan_student is available we can
• use
• for (i 0 i lt MAX_STU i)
• scan_student(stu_listi)
• To fill the array and
• for (i 0 i lt MAX_STU i)
• printf(d\t.2f\n, stu_listi.id,
  stu_listi.gpa)
• To print the array contents

24
Case Study

• Problem Write a program that takes a measurement
  in one unit (e.g. 4.5 quarts) and converts it to
  another unit (e.g. liters).
• Structured data type
• unit_t components
• name / e.g. milligrams /
• abbrev / e.g. mg /
• class / liquid_volume, distance, or
  mass /
• standard / number of standard units equivalent
  to this /

25
Case Study

• typedef struct / unit of
  measurement type /
• char nameNAME_LEN / character string
  such as "milligrams" /
• char abbrevABBREV_LEN/ shorter
  character string such as "mg" /
• char classCLASS_LEN / character string
  such as "pressure",
• "distance",
  "mass" /
• double standard / number of
  standard units equivalent
• to this unit
  /
• unit_t
• int fscan_unit(FILE filep, unit_t unitp)
• void load_units(int unit_max, unit_t units, int
  unit_sizep)
• int search(const unit_t units, const char
  target, int n)
• double convert(double quantity, double old_stand,
  double new_stand)

26

• Data File and Sample Run of Measurement
  Conversion Program
• Data file units.dat
• miles mi distance
  1609.3
• kilometers km distance
  1000
• yards yd distance
  0.9144
• meters m distance 1
• quarts qt liquid_volume
  0.94635
• Sample run
• Enter a conversion problem or q to quit.
• To convert 25 kilometers to miles, you would
  enter
• gt 25 kilometers miles
• or, alternatively,
• gt 25 km mi
• gt 450 km miles
• Attempting conversion of 450.0000 km to miles . .
  .
• 450.0000km 279.6247 miles
• Enter a conversion problem or q to quit.
• gt 2.5 qt l

27
Common Programming Errors

• Incorrect use of direct component selection .
• Indirect component selection -gt can solve the
  problem of operator precedence of .
• There is no comparison operator on structure
  types and they can not directly used in printf
  and scanf