arrays & structures ii chapter 9. 2 organizing heterogeneous data arrays allow a programmer to...
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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 Destination Miles Time----------------------------------------------------------Blacksburg, VA Knoxville, TN 244 3:25Knoxville, TN Nashville, TN 178 2:35Nashville, TN Memphis, TN 210 3:17Memphis, TN Little Rock, AR 137 2:05Little Rock, AR Texarkana, TX 141 2:10
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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};
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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
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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;
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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;
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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
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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 anotherX == Y; // _____ comparing two structscout << X; // _____ inserting an struct to a streamX = X + Y; // _____ performing arithmetic with structsreturn X; // _____ using a struct as the return valueFoo(X); // _____ passing an entire struct
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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;}
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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 0-100 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.
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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];
SSN P1 P2 P3 Pavg T1 T2 T3 Tavg Tot Grade Valid
Multidimensional Arrays
13
Multidimensional Arrays
Multidimensional arrays Have more than one index
Rows & Columns for 2-D arrays
Syntax for array declaration:<data type> <var name>[<# elements dim 1>][<# elements dim 2>]
…[<# elements dim N>];
int twoDimArray[4][2];
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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};
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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];
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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];
}
}
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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];
}
}
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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];
}
}
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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];
}
}
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44
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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];
}
}
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iRow
iColumn
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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];
}
}
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iRow
iColumn
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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];
}
}
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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];
}
}
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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])
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