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Structures or Derived Types

Structures or Derived Types. Real Life Objects. Often structured Students , Employees , Cars , Accounts , Cricket matches , flats etc contain heterogeneous sub-objects Students Name ( string ), Age ( integer in [15, 65], ) Height ( real ), CPI ( real number in [1,10] ) Car

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Structures or Derived Types

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  1. Structures or Derived Types

  2. Real Life Objects • Often structured • Students, Employees, Cars, Accounts, Cricket matches, flats etc • contain heterogeneous sub-objects • Students • Name (string), • Age (integer in [15, 65],) • Height (real), • CPI (real number in [1,10]) • Car • Weight (Real), Volume (Real), • Make (String), Seating capacity(Integer) , • Year of make (integer)

  3. Arrays • Two Structured Data Types • Arrays and Character strings • Both are homogeneous: • components are of identical type • Accessing a component through indices • not very natural • More natural data types desirable

  4. Derived Data Types • Fortran's solution to representing general structured data • Heterogeneous collection of data values • Components identified directly by names rather than indices • Generalized random access • Derived data type objects called structures (in C ) and Records (Pascal)

  5. Example Type :: Cricketer Character(len=25) :: Name Integer :: Age Real :: Height Character(len=10) :: Country logical :: in_action Real :: ave_score logical :: bowler end type Cricketer

  6. Structure variables • Variables declared to be of a derived type • Similar syntax used, eg. • Type (Cricketer)::indian_top_scorer_01, england_captain_99, aussie_keeper_74 • Type (Cricketer),Dimension(15)::Indian_Team_02 • The latter is an array of structures or records

  7. Initialization Indian_top_scorer_01 = Cricketer("Tendulkar", 29, 5.2, "India", .true. ... ) England_captain_02 = Cricketer("Hussain", 24, 5.6, "England", .true. , ... ) • Structure Constructor operation(inspired by C++)

  8. Accessing the Components • The components of a structure (a variable of derived type) can be accessed by the names top_scorer%height captain%ave_score Indian_Team_02(i)%ave_score • Each of these is like a variable of appropriate type • can appear wherever such variables can occur • top_scorer%height = 5. • if (captain%ave_score > 25) then • top_scorer%ave_score = … • Int(captain%ave_score) + 26 • Indian_Team_02(i)%ave_score < Eng_Team_02(i)%ave_score

  9. Structure inside structure • Components can be intrinsic types or even other derived types Type:: team_pair character(len=10):: team1 character(len=10):: team2end typeteam_pairType:: matchtype(team_pair):: teamsInteger:: dateCharacter(len=10):: groundCharacter(len=10):: countryend type matchType:: cricketer ...type(match):: top_score_match ...end type cricketer

  10. Component Selection • Any component can be selected using series of component selectors Eg. eng_captain%topscore_match%ground = “Lords” • Recursive Structures • One of the component can be of the parent type itself! • More on this later

  11. Program structure Type:: cricketerCharacter(len=15):: name,countryreal:: averageinteger:: top_scoreend type type(cricketer), dimension(15):: natwest_series_teamcharacter(len=15):: playerreal:: averageinteger:: iread *, natwest_series_teamread *, playerdo i = 1, 15 if (trim(natwest_series_team(i)%name) == player) then average = natwest_series_team(i)%averageprint *, averageexitendifend do

  12. Complex Data Types • Complex data types can be defined as structured data typestype :: Compxreal:: re_partreal:: im_partend type Compx type(Compx):: xyz • But direct support is available in Fortran 90 • Complex data type is an intrinsic type Complex:: a1 = (3.1410, - 2.3456) • declares a1 to be of type complex with given real and imaginary parts

  13. Accessing components • Complex numbers can be read or written component-wisecomplex:: a1 read*, a1 • requires input to be (2.345, 6.7890) • Print command also outputs in the same way • To assign a variable, use a1 = complex(a,b) • a1 will get the value (a,b) • Kind parameter is an optional parameter

  14. Intrinsic Functions • Real(),Int() - throws the imaginary part and converts the real part to real or integer data types • Aimag() - converts the imaginary part to a real number • Cabs(c) - absolute value of c = sqrt(a^2 + b^2)

  15. Example program quadraticimplicit nonereal :: a, b, c, disc, x_rcomplex:: x_c1,x_c2 = (0.0, 0.0)real, parameter :: eps = 1.0e-6read *, a, b, c if (a == 0.0) then! a is 0, not a quadratic equationprint *, "equation is not quadratic"elsedisc = b*b - 4.0*a*c x_r = -b/(2.0*a) if ( abs(disc) < eps ) then! discriminant is nearly zeroprint *, "double real root", x_r else x_c1 = (x_r + Sqrt( Cmplx(disc,0.0))/(2.0*a)) x_c2 = (x_r - Sqrt( Cmplx(disc,0.0))/(2.0*a))print *, Real(x_c1),"+ i", Aimag(x_c1) print *, Real(x_c2),"- i", Aimag(x_c2)endifendifend program quadratic

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