Arrays & Structures II Chapter 9

2 Organizing Heterogeneous Data  Arrays allow a programmer to organize values of the same type  Homogeneous data  What about logically related data values of differing types?  Heterogeneous data  Parallel arrays  Array of structs Origin DestinationMilesTime Blacksburg, VA Knoxville, TN2443:25 Knoxville, TN Nashville, TN1782:35 Nashville, TN Memphis, TN2103:17 Memphis, TN Little Rock, AR1372:05 Little Rock, AR Texarkana, TX1412:10

3 Organizing Heterogeneous Data  A better design would be to have a new data type, Trip, such that a variable of type Trip would contain all the related values for a single trip.  A struct allows C++ programmers to do just that…  Like enum, struct is used to define a new data type  The statement below does not declare a variable, it defines a type struct Trip { string Origin; // starting point of trip string Destination; // ending point of trip int Miles; // distance traveled int Minutes; // time required, in min double MPH; // average speed };

4 Structures  Structure: a heterogeneous collection of data values called members or fields  each member has a type and a unique name  individual members are accessed by name  Definitions of data types are usually global, since they are required throughout a program.  As long as a type definition is in scope we may declare variables of that type in the usual way: Trip firstLeg; const int MAXLEGS = 100; Trip Itinerary[MAXLEGS]; // array of Trips

5 struct Variables  A variable of a struct type will contain the values for all of the specified members for that type  Those members must be individually initialized  To reference a particular member of a struct variable, state the variable name followed by a period followed by the member name  The period is the member selector operator Trip firstLeg; firstLeg.Origin = "Blacksburg, VA"; firstLeg.Destination = "Knoxville, TN"; firstLeg.Miles = 244; firstLeg.Minutes = 205; firstLeg.MPH = 71.2;

6 struct Variables  Accessing struct array elements requires use of both [] and. Operators  First specify the array index  Then the struct member const int MAXLEGS = 100; Trip Itinerary[MAXLEGS]; // array of Trips Itinerary[0].Origin = "Milwaukee, WI"; Itinerary[0].Destination = "Chicago, IL"; Itinerary[0].Miles = 88; Itinerary[0].Minutes = 88; Itinerary[0].MPH = 60.0;

7 Member Access Example struct Rectangle { int color; int xNW, yNW; int Side[2]; };... Rectangle R; cin >> R.xNW >> R.yNW; cin >> R.Side[0] >> R.Side[1]; R.color = 0; int Area = R.Side[0] * R.Side[1]; The members of a struct variable may be used just as if they were simple variables of the specified type

8 Aggregate Operations  An aggregate operation is an operation that is performed on a data structure, such as an structured variable, as a whole rather than performed on an individual member  Which of the following are supported for structs? Trip X, Y; X = Y; // _____ assigning one struct to another X == Y; // _____ comparing two structs cout << X; // _____ inserting an struct to a stream X = X + Y; // _____ performing arithmetic with structs return X; // _____ using a struct as the return value Foo(X); // _____ passing an entire struct

9 struct Variables as Parameters  Entire struct variables can be passed to functions as parameters.  By default is struct is passed by value  Since struct variables tend to be large, it is generally better to pass them by constant reference void printTrip(Trip& aTrip) { cout << aTrip.Origin << endl << aTrip.Destination << endl << aTrip.Miles << endl << (aTrip.Minutes / MINSPERHOUR) << ':' << (aTrip.Minutes % MINSPERHOUR) << endl << aTrip.MPH << endl; }

10 Problem  In a certain class (<=50 students) 3 programming assignments (worth 40%) and 3 tests (worth 60%) are given  All the programming and test scores must be in the range and should be checked for errors  An erroneous score means that student's data is invalid  Compute the average test and programming scores, and overall grades (A through F, based on 90, 80, 70, 60 scale) for each student, as well as class averages  Assume that the data for each student consists of a SSN followed by 6 integers representing the programming and test scores.

11 Processing Student Grades const int MaxStudents=50; struct StudentType { string ssn; int P1, P2, P3, T1, T2, T3; float Pavg, Tavg, Tot; char grade; bool valid; }; StudentType students[MaxStudents]; SSNP1P2P3PavgT1T2T3TavgTotGradeValid

Multidimensional Arrays

13 Multidimensional Arrays  Multidimensional arrays  Have more than one index  Rows & Columns for 2-D arrays  Syntax for array declaration: [ ][ ] …[ ]; int twoDimArray[4][2]; ? ? ? ? ? ? ? ?

14 Initialization  Multidimensional arrays can be initialized like 1-D arrays  List elements in row major order int twoDimArray[4][2] = {3, 25, 9, 16, -4, 4, 44, 2};

15 for Loops  When accessing or performing operations on multidimensional arrays, it is often necessary to use nested for loops. Consider the problem of adding arrays x and y, and placing the result in z. const int NRow = 4; const int NColumn = 2; int x[NRow][NColumn] ={ 3, 25, 9, 16, -4, 4, 44, 2}; int y[NRow][NColumn] ={ 8, 5, 12, -3, 43, 8, -7, 4}; int z[NRow][NColumn];

16 for Loops int iRow; int iColumn; for (iRow = 0; iRow < NRow; iRow++) { for (iColumn = 0; iColumn < NColumn; iColumn++) { z[iRow][iColumn] = x[iRow][iColumn] + y[iRow][iColumn]; } ? ? ? ? ? ? ? ? ? iRow iColumn xyz

17 for Loops int iRow; int iColumn; for (iRow = 0; iRow < NRow; iRow++) { for (iColumn = 0; iColumn < NColumn; iColumn++) { z[iRow][iColumn] = x[iRow][iColumn] + y[iRow][iColumn]; } ? ? ? ? ? ? ? ? iRow iColumn xyz

18 for Loops int iRow; int iColumn; for (iRow = 0; iRow < NRow; iRow++) { for (iColumn = 0; iColumn < NColumn; iColumn++) { z[iRow][iColumn] = x[iRow][iColumn] + y[iRow][iColumn]; } ? ? ? ? ? ? ? iRow iColumn xyz

19 for Loops int iRow; int iColumn; for (iRow = 0; iRow < NRow; iRow++) { for (iColumn = 0; iColumn < NColumn; iColumn++) { z[iRow][iColumn] = x[iRow][iColumn] + y[iRow][iColumn]; } ? ? ? ? ? ? ? iRow iColumn xyz

20 for Loops int iRow; int iColumn; for (iRow = 0; iRow < NRow; iRow++) { for (iColumn = 0; iColumn < NColumn; iColumn++) { z[iRow][iColumn] = x[iRow][iColumn] + y[iRow][iColumn]; } ? ? ? 30 ? ? ? iRow iColumn xyz

21 for Loops int iRow; int iColumn; for (iRow = 0; iRow < NRow; iRow++) { for (iColumn = 0; iColumn < NColumn; iColumn++) { z[iRow][iColumn] = x[iRow][iColumn] + y[iRow][iColumn]; } ? ? ? 30 ? ? ? iRow iColumn xyz

22 for Loops int iRow; int iColumn; for (iRow = 0; iRow < NRow; iRow++) { for (iColumn = 0; iColumn < NColumn; iColumn++) { z[iRow][iColumn] = x[iRow][iColumn] + y[iRow][iColumn]; } ? ? ? 30 ? ? ? iRow iColumn xyz

23 for Loops int iRow; int iColumn; for (iRow = 0; iRow < NRow; iRow++) { for (iColumn = 0; iColumn < NColumn; iColumn++) { z[iRow][iColumn] = x[iRow][iColumn] + y[iRow][iColumn]; } ? ? 30 ? ? ? iRow iColumn xyz

24 Multidimensional Arrays & Functions  Recall, a function using a 1-D array uses pass-by reference as follows: a_function(int x[])  With multidimensional arrays, the array is still passed using pass-by reference, but there is less flexibility.  With the 1-D array we do not have to explicitly state the size of the array  With multidimensional arrays, we do not have to explicitly state the size of the first dimensional, but must do so for remaining dimensions a_function(int x[][N])