1

Principles of Programming I

Note Set #12

2

Semester Overview

FunctionsCharacter File I/O ArraysPointers and Dynamic Memory

AllocationCharacters and StringsStructures/RecordsBinary File I/O

3

Overview

Structured Data

4

Concept

• A structure is a container – It can hold a collection of pre-defined variables

• Used to organize these things into nice, neat packages

5

What’s in a struct?

• Each part in a structure is called a member

• Each member has a name, type and value

• Names of members follow rules of variable names

• Types can be any pre-defined types

6

Simple Structure Definition

struct studentGrades {int hw1; // homework gradesint hw2;int test1; // test gradesint final; // final gradefloat avg; // final average

};

structure name

structure body

7

Using a struct

• By declaring a struct, you are in essence creating a new data type

• Once you have the struct defined, you can now create variables of the new type

studentGrades stu1;studentGrades stu2;

8

Accessing Members

• You can treat the members of a struct just like variables

• Access the members of a struct using ‘.’ notation (dot-notation)

cout << stu1.hw1;cout << stu2.hw1;

2 differentvariables

9

Accessing Members

• Still use ‘.’ notation to store data in struct members.

stu1.test1 = 89;stu2.test2 = 99;

Struct variablename

Member ofstruct

10

Pointers to Strctures

• Because our structure is a type, we can declare a pointer to it.

• We can dynamically allocate a structure

studentGrades *sgPtr;

sgPtr = new studentGrades;

11

Pointers to Strctures

• To access a member with a pointer, we use the indirection operator (->)

studentGrades *sgPtr;

sgPtr = new studentGrades;

sgPtr->test1 = 101;

cout << sgPtr->test1;

cin >> sgPtr->test2;

12

Arrays of Structures

• Since your struct is a type, you can have arrays of the structure.

studentGrades cse1341[15];

cse1341[1].test1 = 93;cse1341[2].hw2 = 15;cout << “Test 1: “ << cse1341[1].test1;

13

Passing Structs

• Can pass to functions by Value, Reference, or Pointer

• Remember: Passing by value won’t change the original parameter from the calling function.

14

Passing By Value

//in maincout << stu1.avg;updateAvg(stu1);cout << stu1.avg;

void updateAvg(studentGrades sg){ float sum = sg.hw1 + sg.hw2 +sg.test1 + sg.final; sg.avg = sum/220;}

Won’t Work!!!

15

Passing By Reference

//in maincout << stu1.avg;updateAvg(stu1);cout << stu1.avg;

void updateAvg(studentGrades &sg){ float sum = sg.hw1 + sg.hw2 +sg.test1 + sg.final; sg.avg = sum / 220;}

Pass byReference

16

Passing by Pointer

//in maincout << stu1.avg;updateAvg(&stu1);cout << stu1.avg;

void updateAvg(studentGrades * sg){ float sum = sg->hw1 + sg->hw2 +sg->test1 + sg->final; sg->avg = sum/220;}

17

DON’T DO THIS!

• Can’t initialize members in struct definition!

struct geoInfo{ char cityName[25]=“Dallas”; char state[15]; unsigned int population=3000000;};

18

Where to put struct definitions

• Can define anywhere before they are used.

• Typically (and required for 1341) they are placed in a separate file called a header file myStructFile.h.

• Use #include “myStructFile.h”

quotes for your own header files

19

Structure Exercise

• Write a program that uses the geoInfo struct. We need to be able to keep track of up to 10 cities and need functionality that will allow us to find the average population of all the cities.

20

Arrays of Structures

struct payInfo{

int hours;float payRate;

};

An Array of 5 payInfo Structures would be:

payInfo employees[5];

21

Arrays of Structures

cout << “Enter the hours worked by 5 “ << “employees and their hourly” << “ rates.” << endl;for (int i = 0; i < 5; i++){ cout << “Emp “ << i+1 << “:”; cout << “ Hours: “; cin >> employees[i].hours; cout << “ Pay Rate: “; cin >> employees[i].payRate;}

22

Arrays of Structures

• Write a function that will calculate and return the total amount the company will have to pay out for the 5 employees for the pay period.

23

Defining and Initializing

payInfo worker1 = {40, 5.75};

payInfo emps[3] = { {40, 5.75}, {32, 9.00},

{41, 15.00} };

payInfo Worker[50] = { {0} };

Initializes the 1st member of the 1st element to this, and the rest

to 0, just like before…

24

Defining and Initializing

• Declare an array of 5 payInfo structs and initialize the hours member to 40.

payInfo abc[5] = { {40}, {40}, {40}, {40}, {40} };

25

Nested Structures

• A structure can be a member of another structure

• A structure can not have a member of its own data type. However, it can have a pointer to its own datatype

26

Nested Structuresstruct date{ int mon; int day; int yr;};struct place{ char street[20]; char city[10]; char state[2]; char zip[7];};

struct empInfo{ char name[20]; int payRate; date birthDate; place homeAddy;};

27

Using Nested Structrues

empInfo emp1;strcpy(emp1.name, “John Doe”);emp1.payRate = 5.75;emp1.birthDate.mon = 8;emp1.birthDate.day = 18;emp1.birthDate.yr = 1965;strcpy(emp1.homeAddy.street, “Airline”);strcpy(emp1.homeAddy.city, “Dallas”);strcpy(emp1.homeAddy.state, “TX”);strcpy(emp1.homeAddy.zip, “75275”);

28

Nested Structuresstruct empInfo{ char Name[20]; int payRate; date birthDate; place homeAddy;}

Notice that we are moving towards grouping variables together that represent one

thing or one concept.

29

Nested Structures

struct locat {float x; locat y; locat z;

};

Structure can’t havea member whosedata type is thatstructure

30

Nested Structures

struct node {int pieceOfData;node * next;

};

Used in a very powerful data structure called the linked list.

31

Structure Storage

struct myLilStruct{ int myInt; float myFloat; char myChar[5];};

32

More withStructures

andFunctions

33

Structures and Functions

struct rectangle {float length;float width;

};

34

Structures and Functions

void display(rectangle r){ cout << r.length << endl;

cout << r.width << endl;}int main(){

rectangle r = {5, 10};display(r);return 0;

}

35

Structures and Functionsrectangle getInput(){

rectangle rec;cout << “Enter length: “;cin >> rec.length;cout << “Enter width: “;cin >> rec.width;return rec;

} int main(){

rectangle r; r = getInput();return 0;

}

36

Questions??

?