C++ Functions and Structs
sandeep@45
07-csci515-StructsandEnums.pdf
Records
◼ Recall that elements of arrays must all be of the same type
◼ In some situations, we wish to group elements of different
types
scores : 85 79 92 57 68 80 . . .
0 1 2 3 4 5 98 99
employee R. Jones 123 Elm 6/12/55 $14.75
Records (structs)
◼ struct: collection of a fixed number of components
(members), accessed by name
◼ Syntax:
C++ Programming: From Problem
Analysis to Program Design, Seventh
Edition
4
◼ C++ struct
◼ structured data type
◼ Fixed number of Components
◼ Components can be of different types, Called members (or fields)
◼ Accessed by name, not by index
◼ struct is a reserved word
◼ No memory is allocated for a struct
◼ Memory when variables are declared
◼ A struct is a definition, not a declaration
◼ Must declare a variable of that type to use it
struct employeeType
{
string firstName;
string lastName;
string address1;
string address2;
double salary;
string deptID;
};
struct studentType
{
string firstName;
string lastName;
char courseGrade;
int testScore;
int programmingScore;
double GPA;
};
//variable declaration
studentType newStudent;
studentType student;
//variable declaration
employeeType newEmployee;
employeeType employee;
◼ Note
◼ You can also declare struct variables when you define the struct.
For example, consider the following statements:
struct studentType
{
string firstName;
string lastName;
char courseGrade;
int testScore;
int programmingScore;
double GPA;
} tempStudent;
struct studentType
{
string firstName;
string lastName;
char courseGrade;
int testScore;
int programmingScore;
double GPA;
};
//variable declaration
studentType tempStudent;
◼ Typically, in a program,
◼ a struct is defined before the definitions of all of the functions in
the program
◼ so that the struct can be used throughout the program.
#include <iostream> using namespace std;
struct Employee {
short id; int age; double wage;
};
void printInformation(Employee employee) {
cout << "ID: " << employee.id << "\n"; cout << "Age: " << employee.age << "\n"; cout << "Wage: " << employee.wage << "\n";
}
int main() {
Employee joe = { 14, 32, 24.15 }; Employee frank = { 15, 28, 18.27 };
// Print Joe's information printInformation(joe);
cout << "\n";
// Print Frank's information printInformation(frank);
return 0; }
◼ Structures DO have aggregate operators
◼ assignment statement =
◼ parameter (value or reference)
◼ return a structure as a function type
◼ Limitations on aggregate operations
◼ no I/O
◼ no arithmetic operations
◼ no comparisons
cin>>newStudent; Cout<<newStudent
studentType temp; temp=newStudent+student;
if (student == newStudent) //illegal
Accessing struct Members
◼ Syntax to access a struct member:
◼ The dot (.) is called the member access operator
◼ To initialize the members of newStudent:
newStudent.GPA = 0.0; newStudent.firstName = "John"; newStudent.lastName = "Brown";
Assignment
◼ Value of one struct variable can be assigned to another
struct variable of the same type using an assignment
statement
◼ The statement:
◼ copies the contents of newStudent into student
student = newStudent;
◼ The assignment statement:
is equivalent to the following statements:
student.firstName = newStudent.firstName;
student.lastName = newStudent.lastName;
student.courseGrade = newStudent.courseGrade;
student.testScore = newStudent.testScore;
student.programmingScore = newStudent.programmingScore;
student.GPA = newStudent.GPA;
student = newStudent;
student = newStudent;
Comparison (Relational Operators)
◼ Compare struct variables member-wise
◼ No aggregate relational operations allowed
◼ To compare the values of student and newStudent,
◼ compare them member-wise,
if (student == newStudent) //illegal
if (student.firstName == newStudent.firstName && student.lastName == newStudent.lastName)
.
.
.
Input/Output
◼ No aggregate input/output operations on a struct variable
◼ Data in a struct variable must be read or written one member
at a time
◼ Example: read values from the keyboard and store them in members,
respectively
◼ Example: output newStudent contents
cin >> newStudent.firstName;
cin >> newStudent.testScore >> newStudent.programmingScore;
cout << newStudent.firstName << " " << newStudent.lastName
<< " " << newStudent.courseGrade
<< " " << newStudent.testScore
<< " " << newStudent.programmingScore
<< " " << newStudent.GPA << endl;
struct Variables and Functions
◼ A struct variable can be passed as a parameter by value
or by reference
◼ A function can return a value of type struct
void printStudent(studentType student)
{
cout << student.firstName << " " << student.lastName
<< " " << student.courseGrade
<< " " << student.testScore
<< " " << student.programmingScore
<< " " << student.GPA << endl;
}
void readIn(studentType& student)
{
int score;
cin >> student.firstName >> student.lastName;
cin >> student.testScore >> student.programmingScore;
cin >> student.GPA;
score = (newStudent.testScore + newStudent.programmingScore) / 2;
if (score >= 90)
student.courseGrade = 'A’;
else if (score >= 80)
student.courseGrade = 'B';
else if (score >= 70)
student.courseGrade = 'C';
else if (score >= 60)
student.courseGrade = 'D';
else
student.courseGrade = 'F’;
}
readIn(newStudent);
Arrays versus structs
Arrays in structs
◼ Two items are associated with a list:
◼ Values (elements)
◼ Length of the list
◼ Define a struct containing both items:
Arrays in structs (cont’d.)
Arrays in structs (cont’d.)
structs in Arrays
◼ Example:
structs in Arrays (cont’d.)
structs within a struct
Summary
◼ struct: collection of a fixed number of components
◼ Components can be of different types
◼ Called members
◼ Accessed by name
◼ struct is a reserved word
◼ No memory is allocated for a struct
◼ Memory when variables are declared
Enumeration
◼ typedef
◼ Create aliases to previously defined data types
◼ User defined data type
◼ Enumeration
Enumeration Type
◼ Data type: a set of values with a set of operations on them
◼ Enumeration type: is a user-defined type whose value is
restricted to one of several explicitly named constants
(enumerators)
◼ To define an enumeration type, you need:
◼ A name for the data type
◼ A set of values for the data type
◼ A set of operations on the values
Enumeration Type (cont’d.)
◼ You can specify the name and the values, but not the
operations
◼ Syntax:
◼ value1, value2, … are identifiers called enumerators
◼ List specifies the ordering:
value1 < value2 < value3 <...
◼ the default value assigned to value1 is 0, the default value
assigned to value2 is 1, and so on
Enumeration Type (cont’d.)
◼ The enumeration type is an ordered set of values
◼ Default value assigned to enumerators starts at 0
◼ A value used in one enumeration type
◼ cannot be used by another in same block
◼ Same rules apply to enumeration types
◼ declared outside of any blocks
◼ defines a new data type called colors
◼ the values belonging to this data type are BROWN, BLUE, RED,
GREEN, and YELLOW.
◼ defines standing to be an enumeration type.
◼ The values belonging to standing are FRESHMAN, SOPHOMORE,
JUNIOR, and SENIOR.
enum colors {BROWN, BLUE, RED, GREEN, YELLOW};
enum standing {FRESHMAN, SOPHOMORE, JUNIOR, SENIOR};
◼ Consider the following statements:
◼ Consider the following statements:
◼ If two or more enums contain constants with the same names,
this can lead to naming conflicts and compilation errors.
enum grades {'A', 'B', 'C', 'D', 'F’}; enum places {1ST, 2ND, 3RD, 4TH};
enum grades {A, B, C, D, F}; enum places {FIRST, SECOND, THIRD, FOURTH};
enum Status{CONTINUE, WON, LOST}; enum mathStudent {JOHN, BILL, CINDY, LISA, RON}; enum compStudent {SUSAN, CATHY, JOHN, WILLIAM};
Can and Can't
◼ You can specify the name and the values, but not the operations
◼ Can
◼ Declare Variables
◼ Assignment statements
◼ Relational Operators
◼ Functions
◼ Can't
◼ No arithmetic operations
Declaring Variables (Can do)
◼ Syntax:
Example:
◼ Can declare variables such as:
◼ Can also declare variables when defining the enumeration type
enum sports {BASKETBALL, FOOTBALL, HOCKEY, BASEBALL, SOCCER, VOLLEYBALL};
sports popularSport, mySport;
enum sports {BASKETBALL, FOOTBALL, HOCKEY, BASEBALL, SOCCER, VOLLEYBALL} popularSport, mySport;
enum {BASKETBALL, FOOTBALL, HOCKEY, BASEBALL, SOCCER, VOLLEYBALL} popularSport, mySport;
Assignment statement (Can do)
◼ Use the variable and set it’s value
◼ Values can be stored in enumeration data types:
◼ Stores FOOTBALL into popularSport
sports popularSport;
popularSport = FOOTBALL;
int num= 0;
bool flag= false;
◼ Consider the following statements:
int num= "A" ;
bool flag= 1.42;
sports popularSport;
popularSport = SUMMER;
enum sports {BASKETBALL, FOOTBALL, HOCKEY, BASEBALL, SOCCER, VOLLEYBALL};
popularSport = FOOTBALL;
popularSport = BASEBALL;
popularSport = 1;
popularSport = 3;
Short summary
◼ Declaration
◼ Instantiation
◼ Operation
enum sports {BASKETBALL, FOOTBALL, HOCKEY, BASEBALL, SOCCER, VOLLEYBALL};
Reserved word enum type
(list of constants separated by commas) Enumerators
0 1 5
sports popularSport, mySport;
popularSport = FOOTBALL; popularSport = BASEBALL;
Can and Can't
◼ You can specify the name and the values, but not the
operations
◼ Can
◼ Declare Variables
◼ Assignment statements
◼ Relational Operators
◼ Functions
◼ Can't
◼ No arithmetic operations
Relational Operators
◼ We can apply relational operatiors
if( num == 1 )
//do something
if( flag == false )
//do something
if (popularSport >= FOOTBALL)
//do something
◼ An enumeration type is an ordered set of values:
FOOTBALL <= SOCCER //is true
HOCKEY > BASKETBALL //is true
BASEBALL < FOOTBALL //is false
enum sports {BASKETBALL, FOOTBALL, HOCKEY, BASEBALL,
SOCCER, VOLLEYBALL};
◼ An enumeration type is similar to an integral data type
and can be used in loops:
◼ Question:
for (popularSport= BASKETBALL; popularSport <= SOCCER;
popularSport = static_cast<sports>(popularSport + 1))
popularSport = static_cast<sports>(popularSport + 1))
How to understand it
Input /Output of Enumeration Types
◼ Input and output are defined only for built-in data types such
as int, char, and double.
◼ An enumeration type cannot be input/output (directly)
◼ Have an integer/a string value and convert it to the enum type
◼ Output: by default, you'll get the integer value of the enum. If you want
to do something fancier than that, you'll have to handle it specially.
cin>>num;
cout<<num<<endl;
cin>>flag;
cout<<flag<<endl;
◼ Input
◼ or
int inputSport;
cin>>inputSport;
popularSport = static_cast<sports>(inputSport);
String inputStr;
cin>>inputStr;
if(inputStr == “BASKETBALL”)
popularSport = BASKETBALL;
if(inputStr == “FOOTBALL”)
popularSport = FOOTBALL;
sports to_enum(string &str)
{
if (str == "BASKETBALL")
return BASKETBALL;
else if (str == "FOOTBALL")
return FOOTBALL;
else if (str == "HOCKEY")
return HOCKEY;
//add more statements
return -1; // -1 in case the
parameter wasn't valid
}
String inputStr;
cin>>inputStr;
popularSport=to_enum(inputStr);
◼ Output
int inputSport;
cin>>inputSport;
popularSport = static_cast<sports>(inputSport);
cout<< popularSport<<endl;
◼ Alternative way
switch(popularSport){
case BESKETBALL:
cout<<"BESKETBALL"<<endl; break;
case FOOTBALL:
cout<<"FOOTBALL"<<endl; break;
case HOCKEY:
cout<<"HOCKEY"<<endl; break;
case BASEBALL:
cout<<"BASEBALL"<<endl; break;
case SOCCER:
cout<<"SOCCER"<<endl; break;
case VOLLEYBALL:
cout<<"VOLLEYBALL"<<endl; break;
default:
}
◼ Use a function Void printSports(sports& var){
switch(var){
case BESKETBALL:
cout<<"BESKETBALL"<<endl; break;
case FOOTBALL:
cout<<"FOOTBALL"<<endl; break;
case HOCKEY:
cout<<"HOCKEY"<<endl; break;
case BASEBALL:
cout<<"BASEBALL"<<endl; break;
case SOCCER:
cout<<"SOCCER"<<endl; break;
case VOLLEYBALL:
cout<<"VOLLEYBALL"<<endl; break;
default:
}
}
printSports(popularSport);
Functions and Enumeration Types
◼ Enumeration types can be passed as parameters to
functions either by value or by reference
◼ A function can return a value of the enumeration type
sports to_enum(string &str)
{
if (str == "BASKETBALL")
return BASKETBALL;
else if (str == "FOOTBALL")
return FOOTBALL;
else if (str == "HOCKEY")
return HOCKEY;
//add more statements
return -1; // -1 in case the
parameter wasn't valid
}
String inputStr;
cin>>inputStr;
popularSport=to_enum(inputStr);
◼ Use a function Void printSports(sports& var){
switch(var){
case BESKETBALL:
cout<<"BESKETBALL"<<endl; break;
case FOOTBALL:
cout<<"FOOTBALL"<<endl; break;
case HOCKEY:
cout<<"HOCKEY"<<endl; break;
case BASEBALL:
cout<<"BASEBALL"<<endl; break;
case SOCCER:
cout<<"SOCCER"<<endl; break;
case VOLLEYBALL:
cout<<"VOLLEYBALL"<<endl; break;
default:
}
}
printSports(popularSport);
Can and Can't
◼ You can specify the name and the values, but not the
operations
◼ Can
◼ Declare Variables
◼ Assignment statements
◼ Relational Operators
◼ Functions
◼ Can't
◼ No arithmetic operations
Can not do
◼ No arithmetic operations are allowed on enumeration
types
◼ ++ and -- are illegal, too:
◼ Solution: use a static cast
mySport = popularSport + 2; //illegal popularSport = FOOTBALL + SOCCER; //illegal popularSport = popularSport * 2; //illegal
popularSport++; //illegal popularSport– –; //illegal
popularSport = static_cast<sports>(popularSport + 1);
◼ After the second statement, the value of popularSport is HOCKEY.
◼Similarly, the statements:
◼ result in storing BASKETBALL in popularSport.
popularSport = FOOTBALL; popularSport = static_cast<sports>(popularSport + 1);
popularSport = FOOTBALL; popularSport = static_cast<sports>(popularSport - 1);
Problem 3
◼ Define an enumeration type Days, that has the values
◼ Sunday,Monday,Tuesday,Wednesday,Thursday,Friday,Saturday
◼ Write a problem that prompts the user to input a value
between 0 and 6 and outputs if it is weekend or not
◼ Example run 1:
◼ Example run 2:
Please enter the day of the week (0 to 6) 5
Emily still at work
Please enter the day of the week (0 to 6) 0
It is the weekend.
Exercises
◼ Q1: what is wrong with the following program?
◼ Q2: Consider the following C++ code:
◼ Q3: Consider the following function definition:
◼
◼ Write the function prototypes of func
◼ Q4: Write the definition of a void function with three
reference parameters of type int, double, and string. The
function sets the values of the int and double variables to
0 and the value of the string variable to an empty string
