what is a stream? what is the difference between an input stream and an output stream?

1. Questions about File I/O • what is a stream? • what is the difference between an input stream and an output stream? • what streams do not need definitions? • how can a stream be defined? • what do the following functions do? • open()close() • c_str() eof()fail()exit() • can a stream be passed as a parameter? How?

2. Structures

3. Structure Definitions • structures are an aggregate construct – used to refer to a collection of diverse data by one name • example: bank’s certificate of deposit (CD) - has balance (double), rate (double) and months until maturity (int) • structure definition: struct CDAacct{ double balance; int rate; int term; }; • note the semicolon at the end of the structure definition! • elements of the structure are called members or member variables • a 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

4. Preprocessor Directives • Recall that each definition (including structure definitions) can only be encountered once during compilation. • When a structure definition is placed in a header file, careful must be taken so it is not read twice • mechanism - preprocessor directives #define name value note that substitution is textual • problem: #define press 50 int press = 30 • gets substituted as int 50 = 30 => syntax error! #ifdef name - true if name defined, #ifndefname - 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

5. Structure Variables • when a structure like CDAcct is defined, structure variables can be declared as any other variables: CDAcct myacct, youracct; • each structure variable contains three member variables • the programmer can refer to member variables by specifying the structure variable name “dot” member variable name • for example myacct contains: myacct.balance myacct.rate myacct.term • the member variables are of type specified in the structure definition • the member variables can be used as any other variables myacct.balance=1000.00; myacct.rate = youracct.rate+1; cin >> myacct.term;

6. Assigning Values toStructure Variables • initialization assignment • structure variable can be initialized at definition: CDacct myacct={1000.0, 9.9, 12} • order of initialization corresponds to the order the member variables are listed in the structure definition • if there are more values than variable members - error • if there are less values than variable members - the rest are initialized to 0 • a structure variable can be assigned the value of another structure variable provided they have the same structure type CDacct youracct; youracct=myacct; • However, structure variables cannot be compared directly if (youracct == myacct) // error

7. Passing Structures as Parameters,Returning Structures • structures can be passed by value and by reference, a function can return a structure: CDaccount setCD(double b, double r, int t){ CDAccount tmp; tmp.balance=b; tmp.rate=r; tmp.term=r; return tmp; }

8. Complex Structures • a member may be of basic type or of type structure (referred to as substructure): // example structure struct example{ int a; string b; }; // second example structure // whose member is a substructure struct compExample{ int c; example d; }; • if there is a declaration compExample me;how do we access substructure member variables?

9. Structures and Arrays • a member may be an array struct example{ // defining structure int a; int b[5]; }; example se; // declaring structure variable se.a = 123; se.b[3]=456; // accessing members • an array of structures may be declared struct example{ // defining structure int a; string b; }; example se[4]; // declaring array of structures se[3].a=123; se[3].b=”Hello”; // accessing members how do we access elements of string b? • more complicated constructs (arrays of structures with substructures, etc.) are possible