1. Structures
putting data together

2. Structure Definitions
aggregate construct allows to manipulate several data items as a single whole
structures are an aggregate construct;
what other aggregate constructs have we studied?
example: a particular date has month, day and year
structure definition:
struct Date{
int month;
int day;
int year; };
note the semicolon at the end of the structure definition
elements of the structure are called members or member variables
structure definition is not executable – good candidate for a header file
members of the same structure must have different names, different structures can contain members with the same name
that is: the scope of member variable name is the structure definition

3. Preprocessor Directives (Review)
each definition (e.g. global constant def.) can be encountered only once during compilation
when definition is placed in a header file, it may be included multiple times
header file must structured so it is safe in case of multiple inclusion; term – multiple inclusion protection
mechanism - preprocessor directives
#define name value note that substitution is textual
problem: #define press 50+5
int myvar = press * 20;
changes order of operations, do not use #define instead of global constants
#ifdef name - true if name defined, #ifndef name - true if not
#endif - completes #if
header file myheader.h containing definitions usually has the following structure:
#ifndef MYHEADER_H
#define MYHEADER_H
// text of the header file goes here
#endif

4. Structure Variables
when structure Date is defined it becomes a type; a structure variables can be declared as any other variable:
Date today, birthday;
each structure variable of Date contains three member variables
programmer can refer to member variable by specifying structure variable name “dot” member variable name
for example today contains:
today.month
today.day
today.year
member variables are of type specified in the structure definition
a member variable can be used as any other (scalar) variable today.year=2001;
today.day = birthday.day+1;
cin >> today.month;

5. Assigning Value to Structure Variable
initialization
structure variable can be initialized at declaration:
Date birthday={10, 31, 2035};
order of initialization corresponds to the order member of member variables in structure definition
more values than variable members – error
less values than variable members – the rest initialized to zero
structure variable can be assigned the value of another structure variable of the same structure type
Date deadline;
deadline=today;
structure variables cannot be directly compared
if (deadline == today) // error
how would you compare two structure variables?

6. Passing Structures as Parameters, Returning Structures
structures can be passed by value and by reference, a function can return a structure:
Date setDate(int m, int d, int y){
Date tmp;
tmp.month=m;
tmp.day=d;
tmp.year=y;
return tmp; }
what does this code do?
Date projectDue;
projectDue=setDate(10,31,2035);

7. Complex Structures a member may be of basic type or of type structure
substructure – member variable of type structure
// example structure
struct Example{
int a;
string b; };
// example complex structure
struct CompExample{
int c;
Example d; // substructure
if there is a declaration compExample me; how do you access substructure member variables?

8. Structures and Arrays a member may be an array
struct ExampleWArray{ // complex structure definition
int a;
int b[5]; // member array };
ExampleWArray se; // declaring structure variable
se.a = 123; se.b[3]=456; // accessing members
an array of structures may be declared
struct Example{ //structure
string b;
Example as[4]; // declaring array of structures
as[3].a=123; as[3].b=”Hello”; // accessing members
how do you access characters of string b?
more complicated constructs (arrays of structures with substructures, etc.) are possible