C++ For Science and Engineering Lecture 8

Transcription

1 C++ For Science and Engineering Lecture 8 John Chrispell Tulane University Friday 10, 2010

2 Arrays Structures are ways of storing more than one type of information together. A structure is a vesatile data form that can hold items fo more thatn one data type. They allow you to unify your data representation. They are user defined types, with a structure declaration serving to define the types data properties. John Chrispell, Friday 10, 2010 slide 3/29

3 Arrays Suppose that you are in need a storing information about designer inflatables that has: name volume price A C/C++ structure that will allow for this is: s t r u c t i n f l a t a b l e { // s t r u c t u r e d e c l a r a t i o n char name [ 2 0 ] ; // s t r u c t u r e members f l o a t volume ; double p r i c e ; } ; The keyword struct indicates that the code defines the layout for a new structure. The identifierinflatable, is the name or tag given to the structure. John Chrispell, Friday 10, 2010 slide 5/29

4 Arrays Once we have this template in place we can create variables of this type. i n f l a t a b l e hat ; // C++ type i n f l a t a b l e v a r i a b l e i n f l a t a b l e w o o p i e c u s h i o n ; // C++ s t r u c t i n f l a t a b l e goose ; // C r e q u i r e s word s t r u c t i n f l a t a b l e v i n c e n t ; Note that unlike in C we do not need to use struct in the declaration. We use the membership operator (.) to access individual members in the structure. Lets look at an example: John Chrispell, Friday 10, 2010 slide 7/29

5 structur.cpp #i n c l u d e <i o s t r e a m > s t r u c t i n f l a t a b l e // s t r u c t u r e d e c l a r a t i o n { char name [ 2 0 ] ; f l o a t volume ; double p r i c e ; } ; i n t main ( ) { using namespace std ; i n f l a t a b l e g u e s t = { G l o r i o u s G l o r i a, // name v a l u e , // volume v a l u e // p r i c e v a l u e } ; // g u e s t i s a s t r u c t u r e v a r i a b l e o f type i n f l a t a b l e // I t s i n i t i a l i z e d to the i n d i c a t e d v a l u e s i n f l a t a b l e p a l = { Audacious Arthur, , } ; / p a l i s a second v a r i a b l e o f type i n f l a t a b l e / cout << Expand your guest l i s t with << guest. name ; cout << and << p a l. name <<! \ n ; / p a l. name i s the name member o f the p a l v a r i a b l e / cout << You can have both f o r $ ; cout << g u e s t. p r i c e + p a l. p r i c e <<! \ n ; } return 0 ; John Chrispell, Friday 10, 2010 slide 9/29

6 Note on the structur.cpp file The structure was defined external to the program and can be used by all the functions in the file. If we had included the structrue definition inside the main function it can only be used inside the main function. Note the initialization can be done on separate lines or all together in one. Depending on your compiler you may be able to use a string inside the structure for the name field. You can also assign one structure to another. John Chrispell, Friday 10, 2010 slide 11/29

7 assgnst.cpp #i n c l u d e <iostream > #i n c l u d e <s t r i n g > s t r u c t i n f l a t a b l e { s t d : : s t r i n g name ; f l o a t volume ; double p r i c e ; } ; i n t main ( ) { } using namespace std ; i n f l a t a b l e bouquet = { s u n f l o w e r s, , } ; i n f l a t a b l e c h o i c e ; cout << bouquet : << bouquet. name << f o r $ ; cout << bouquet. p r i c e << e n d l ; c h o i c e = bouquet ; / a s s i g n one s t r u c t u r e to a n o t h e r / cout << c h o i c e : << c h o i c e. name << f o r $ ; cout << c h o i c e. p r i c e << e n d l ; return 0 ; John Chrispell, Friday 10, 2010 slide 13/29

8 A struct with no typename! You can create a structure with no type name. You do this by omitting a tag name while simultaneously defining a structure form and a variable: s t r u c t { // No tag i n t x ; i n t y ; } p o s i t i o n ; // a s t r u c t u r e v a r i a b l e You can use the membership operator with the variable position now, as in position.x. Note there is no general name for the type. We can now consider the following listing with an array of structs: John Chrispell, Friday 10, 2010 slide 15/29

9 arrstruc.cpp #i n c l u d e <i o s t r e a m > s t r u c t i n f l a t a b l e { } ; char name [ 2 0 ] ; f l o a t volume ; double p r i c e ; i n t main ( ) { using namespace std ; / ========================================== / / I n i t a l i z e two i n f l a t a b l e s / / ========================================== / i n f l a t a b l e g u e s t s [ 2 ] = { { Bambi, 0. 5, }, { Godzilla, 2000, } } ; / ========================================== / / Display some information about the s t r u c t s / / ========================================== / cout << The guests << guests [ 0 ]. name << and << guests [ 1 ]. name << \ nhave a combined volume o f << g u e s t s [ 0 ]. volume + g u e s t s [ 1 ]. volume << c u b i c f e e t. \ n ; } return 0 ; John Chrispell, Friday 10, 2010 slide 17/29

10 Unions A union is a data format that can hold different data types but only one at a time. The format is close to that of a structure. union o n e 4 a l l { i n t i n t v a l ; long l o n g v a l ; double d o u b l e v a l ; } ; You can use a one4all to hold an int, a long, or a double as long as you do so at different times: o n e 4 a l l p a i l ; p a i l. i n t v a l = 1 5 ; cout << p a i l. i n t v a l ; p a i l. d o u b l e v a l = ; // the i n t v a l u e i s l o s t! cout << p a i l. d o u b l e v a l ; John Chrispell, Friday 10, 2010 slide 19/29

11 Enumerations An enumeration or enum is nother way of creating a symbolic constants. enum spectrum { red, orange, y e l l o w, green, blue, i n d i g o, v i o l e t } ; / spectrum i s the name o f the new t y p e / This establishes red, orange, yellow, and so on as symbolic constants for the integers 0-6. You can now delcare a variable of type spectrum and set its values: spectrum band ; band = orange ; band = spectrum ( 1 ) ; // same as l i n e above ; You can set the enumerator values explicitly by: enum spectrum { red, orange = 0, y e l l o w, g r e e n = 1 } ; These may be useful later when dealing with switch case statements. John Chrispell, Friday 10, 2010 slide 21/29

12 Pointers and the Free Store When storing data we are interested in: Where the information is stored. What value is kept there. What kind of information is stored. This brings us to finding the address for normal variables: For this we use the address operator, represented by &. If name is a varaible, then &name is its address. Consider the next listing: John Chrispell, Friday 10, 2010 slide 23/29

13 address.cpp #i n c l u d e <iostream > i n t main ( ) { } using namespace std ; i n t donuts = 6 ; double cups = 4. 5 ; cout << donuts v a l u e = << donuts ; cout << and donuts a d d r e s s = << &donuts << endl ; / ============================================ / / NOTE: you may need to use unsigned (& donuts ) / / and unsigned (& cups ) / / ============================================ / cout << cups v a l u e = << cups ; cout << and cups a d d r e s s = << &cups << e n d l ; return 0 ; Here we have treated the value as the named quantity and location as the derived quantity. John Chrispell, Friday 10, 2010 slide 25/29

14 Pointer A pointer is a special type of variable that holds the address of the value. Thus, the name of the pointer represents the location and the value is the derived quantity. Applying the * operator, called the indirect value or the dereferencing operator, yields the value at the location. Consider the following listing: John Chrispell, Friday 10, 2010 slide 27/29

15 pointer.cpp #include <iostream > i n t main ( ) { using namespace std ; i n t updates = 6 ; // d e c l a r e a v a r i a b l e i n t p updates ; // d e c l a r e p o i n t e r to an i n t p updates = &updates ; // a s s i g n ad dre s s of i n t to p o i n t e r / ======================= / / e x p r e s s v a l u e s two ways / / ======================= / cout << Values : updates = << updates ; cout <<, p updates = << p updates << endl ; / ======================== / / e x p r e s s a d d r e s s two ways / / ======================== / cout << Addresses : &updates = << &updates ; cout <<, p updates = << p updates << endl ; / =========================== / / use p o i n t e r to change v a l u e / / =========================== / p u p d a t e s = p u p d a t e s + 1 ; cout << Now updates = << updates << endl ; } return 0 ; John Chrispell, Friday 10, 2010 slide 29/29