Structures putting data together

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

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

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;

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?

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);

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?

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