1 / 12

CS113 Introduction to C

CS113 Introduction to C. Instructor: Ioannis A. Vetsikas E-mail: vetsikas@cs.cornell.edu Lecture 6 : September 6. Create your own types: typedef. #define N 3 typedef double scalar; typedef scalar vector[N]; typedef scalar matrix[N][N];

kawena
Download Presentation

CS113 Introduction to C

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript


  1. CS113Introduction to C Instructor: Ioannis A. VetsikasE-mail: vetsikas@cs.cornell.edu Lecture 6 : September 6

  2. Create your own types: typedef #define N 3 typedef double scalar; typedef scalar vector[N]; typedef scalar matrix[N][N]; void add_vectors( vector x, vector y, vector z ) { int i; for( i = 0; i < N; i++ ) { x[i] = y[i] + z[i]; } } Syntax: typedef <some type> <type name> Way to remember it: typedef <same as a declaration>

  3. Structures • The structure mechanism allows us to aggregate elements of different types • Think of objects (but not quite!) • Your struct definition generally goes outside all functions struct card_struct { int pips; char suit; }; typedef struct card_struct card; struct card_struct { int pips; char suit; } c1, c2; typedef struct card_struct card; void some_function() { struct card_struct a; card b; /* a, b have same types */ b.pips = 3; }

  4. Structures (continued) • Syntax: struct [<name/tag>] { component-declarations } [<variable name(s)>]; • Access elements/fields with dot operator: • b.pips or a.suit • Structure Names/Tags • If a structure type does not have a name, then only a finite number of structures can be created • Structure tags form their own namespace! • Structure fields also form their own namespace…

  5. Structures (continued) • Once a structure is declared you can use it as though it were a default data type (e.g. int) struct point {int x,y;}; struct rect {struct point pt1, pt2;}; • Can return from and also pass structures to functions (call-by-value) int ptinrect (struct point p, struct point r) { return p.x>=r.pt1.x && p.x<r.pt2.x && p.y>=r.pt1.y && p.y<r.pt2.y }

  6. Structures (continued) • Another example of a function: struct point midpoint (struct point a, struct point b) { struct m = {(a.x+b.x)/2, (a.y+b.y)/2}; return m; } • Usually one uses typedef to name the struct in some way and thus does not have to put struct <tag> all the time • What does a=b do, when we have defined struct point a=b ? • Can also define pointers to structures in the same way as for simple data types: • struct point pt, *point_ptr; • We can use the &,* operators in the same way as before: • *point_ptr or &pt

  7. Structures – accessing via pointer struct card_struct { int pips; char suit; }; typedef struct card_struct card; void set_card( card *c ) { c->pips = 3; c->suit = ‘A’; } void main() { card a; set_card( &a ); } If p is a pointer to a structure and x is an element of the structure then to access this element one puts: (*p).x or more commonly p->x

  8. Pointers to Structures (continued) • Call by value: expensive (and slow) to pass structures between functions • Use pointer instead (this simulates call by reference) • Operators -> and . are left-to-right associative and have maximum precedence along with () and [] • e.g. ++pp->x increments field x, not pointer pp

  9. Structures – initialize #include <stdio.h> struct address_struct { char *street; char *city_and_state; long zip_code; }; typedef struct address_struct address; void main() { address a = { "1449 Crosby Drive", "Fort Washington, PA", 19034 }; } You may initialize a variable corresponding to a structure that was defined by initializing all its elements as follows: struct name var = {init_element_1, …, init_element_n}

  10. Unions • Similar to structures, but they can only hold one of the elements at a time • So they use the same spot in memory to save any of the possible elements. • Memory for union is max of memory needed for each element union int_or_float { int i; float f; }; union int_or_float a; /* need to keep track of, on own, which type is held */ /* a.i always an int, a.f always a float */

  11. sizeof Operator • sizeof expression/object or sizeof <type name> returns the size of the type of the expression or the type in bytes • the expression is not evaluated • E.g. sizeof a, sizeof a[13] (a is array) or sizeof int • Typing sizeof a/sizeof a[0] returns? • Cannot be applied to functions

  12. Read from K&R • Covered 6.1-6.4 today Other issues • Homework 2 due on Friday • You MUST print the output exactly in the same way as in the examples which are given • Do not forget to include your name and student ID# when you submit your programs by email + give me printout

More Related