Transcript Introduction to Computer Science

Introduction to Computer Science
COMP 51 – Fall 2012 – Section 2
Structures

2
Business
 Exam 2 next week (Review on Wed)
 Office hours will be next Thurs instead of Tues
 Project 5 – Part A
 Will discuss briefly on Monday
 Due Monday, Nov 26th
 Also on Monday, you will complete Lab 8 (which we
will start today). I will be in class until noon (at
which time I have to leave for a meeting)
3
Structures

4
Structures
 Prior knowledge – Arrays
 Collection of multiple values of the same type
 New concept – Structures
 Collection of multiple values of different types
 Treated as a single item, like arrays
 Several key differences
 Structure elements are accessed by name, not by index
number
 Must first define structure prior to declaring any
variables
5
Why Structures?
 The pieces of data are related in some way
 Easier to keep them together (all in one place)
 Easier to move them around all at once!
 Examples
 Certificate of Deposit at a bank
 Account balance, interest rate, term length
 Time of day
 Hour, minute, second
 Student information record
 First name, last name, student ID number, cell phone,
home phone, campus phone, etc…
6
New Keyword: struct
 The keyword struct is used to create a new
structure
 Each item (member) inside the structure has a
name, just like a variable
 Two (or more) names to keep track of now
 The name of the structure type
 The name(s) of elements inside the structure
7
Define Structure Type
 Define struct globally (typically)
 Example for certificate of deposit account
 Name of structure?
 CDAccount
 Name of members in the structure?
 balance, InterestRate, term
struct CDAccount
{
double balance;
double interestRate;
int term;
};
8
Declare Structure Variable
 Step 1: Define structure type (previous slide)
 Compiler then knows what a “CDAccount” is
 Step 2: Declare a variable with this new structure
type
 Just like declaring an int, float, char, …
 Variable account of type CDAccount
 It contains “member variables”
CDAccount account;
9
Accessing Structure Members
 Individual elements are called “member variables”
 Different structure types can have same member
variable names without conflict
 New operator to access members: .
 Use to read or write a member variable
account.balance
account.interestRate
account.term
A period!
“dot”
10
Structures as Function Arguments
 Passed like any simple data type
 Pass-by-value or Pass-by-reference
 Neat trick: Easily pass multiple data items to a
function!
 Can also be returned by function
 Return type is structure type
 Neat trick: Easily return multiple data items from a
function!
11
Example Program
#include <iostream>
using namespace std;
// Structure for certificate of deposit
struct CDAccount
{
double balance;
double interestRate;
int term;
};
Function returning a struct
Function taking a struct
CDAccount openAccount(void);
void printAccount(CDAccount account);
12
Example Program
int main(void)
{
CDAccount account;
account = openAccount();
printAccount(account);
return 0;
}
Declare a new instance of the
CDAccount structure called “account”
13
Example Program
CDAccount openAccount(void)
{
CDAccount account;
cout << "Enter account balance: $";
cin >> account.balance;
cout << "Enter account interest rate in %: ";
cin >> account.interestRate;
cout << "Enter number of months until maturity: ";
cin >> account.term;
return account;
}
Returns the variable account, which is a structure of type CDAccount
and contains 3 member variables (balance, interestRate, and term)
14
Example Program
void printAccount(CDAccount account)
{
double rateFraction, interestEarned, endBalance;
rateFraction = account.interestRate/100.0;
interestEarned = account.balance*
(rateFraction*(account.term/12.0));
endBalance = interestEarned + account.balance;
cout <<
<<
<<
<<
<<
}
"When your CD matures in "
account.term
" months, it will have a balance of $"
endBalance
endl;
15
Example Output
Enter account balance: $100.00
Enter account interest rate in %: 10.0
Enter number of months until maturity: 6
When your CD matures in 6 months, it
will have a balance of $105
16
Pitfall – Required Semicolon!
 Semicolon after structure definition is required!
 struct WeatherData
{
double temperature;
double windVelocity;
};  semicolon!
 Required since you can declare structure
variables in this location
17
Pitfall – Initialization
 Member variables cannot be initialized in the
declaration
 The structure definition only defines the types,
names and order of members
 struct WeatherData
{
double temperature = 32.0;
double windVelocity = 10;
};
This is not allowed
18
Uniqueness of Names
 Different structures may use the same member
variables names without confusion
struct CDAccount
{
double balance;
double interestRate;
int term;
};
struct CheckingAccount
{
double balance;
double interestRate;
};
 Names within a structure still have to be unique,
however
19
Structure Assignments

An entire structure can be copied in a single statement (in
contrast to arrays, which must be element by element)

Declare two structure variables



CDAccount account1;
CDAccount account2;
// Set data in account1
account2 = account1;
Simply copies each member variable from apples
into member variables from oranges
Can’t do anything else, however 


No comparisons (==, >, <, etc.)
At least not without extra programming work…
20
Arrays of Structures
 An array of 10,000 CD account structures
 CDAccount accounts[10000];
 Accessing an element of the structure in the array
 cout << “Account #10 balance is $”
<< accounts[10].balance
<< endl;
 Structures can have elements that are arrays, too
21
Lab 8: Structures Exercise

22
Lab 8
 You’re going to create a program to store
information about a team of fencers at a
tournament.
 Create a Fencer structure to store the first name,
weapon and scores from 2 bouts for each fencer.
There are three possible weapons: “foil”, “epee”
and “saber”. The scores for a bout are integers
between 0 and 15.
23
Lab 8
 Create an array of 5 Fencers. This array should be
declared in main(). You will pass it to functions that use
it. (Remember that arrays are always passed by
reference to functions).
 Create a function to prompt the user for information
about each fencer and fill it into the array

getTeam(Fencer team[], int teamSize);
 Create a function to print out the name, weapon and
highest score of each fencer on the team.

printTeam(Fencer team[], int teamSize);
24
Lab 8
 Create a function to ask the user to select a weapon
and then print out the names of all the fencers who
use that particular weapon.
 weaponChoice(Fencer team[], int teamSize);
 Call these three functions in sequence inside
main().
25
Lab 8
Sample input and output
26
Questions?
?