1. CSC 107 – Programming For Science

2. Today’s Goal  Learn what structures are & how they are used  Why we need & why would use a structure  What fields mean and how they are declared  How variables of struct type work and interact

3. All About the Variables  Variable names location to store data  Memory location's initial value is unknown  Assignments update memory location with new value  Value at memory location used in place of variable  Type specified for each variable declared  Type defines exactly how variable can be used  Implicitly defines memory needed for variable  Specifies how the memory location set & interpreted

4. Problem With Variables  What type can be used for this:

5. Problem With Variables  Is putting an int, double, or cString

6. Problem With Variables  What is the data type describing this action?

7. Problems With Variables  Sometimes need to group data  Pixels: red, green, blue, & alpha components  Forces: mass & vector of acceleration  Atomic Particles: position & charge & spin  Students: name, assignments, programs, & tests  Would like to do this within single variable  But requires multiple values defined for each variable  Normally want to do this for many variables

8. What Is a struct ?  Similar to real-world blueprint or schematic  Outlines how to group items to make bigger thing  May/will have to end up making many copies of item  No change to others when single item changed

9. Creating A struct  Declare struct outside of any function  After #include s where normally find declarations  Each struct must be given name  Follows normal naming rules & conventions  Within struct, must declare 1 or more fields  Name & data type required for each field  Fields can be listed in any order  Act like variables belonging to each copy of struct  Each struct variable gets own copy of fields

10. Declaring A Struct

14. Using structs

15.  Type of the variable is specific struct  Variable gets own copy of all of the fields  Like variable or array entry, initial values unknown  No link between fields even if names are same same struct, fields not linked  Even variables of same struct, fields not linked

16. Variables of struct Type struct color { int red, green, blue; }; int main(void) { struct color yellow = { 158, 154, 0 }; struct color purple; purple.red = 102; purple.green = 102; // Better way to initialize purple.blue = 152; cout << yellow.red << " != " << purple.red;

17. Using struct s variables  Can assign struct variables to one another  Variables must be of identical struct types  Copies value of all fields but still remain independent  Locations will be same, since pointers & arrays aliased  In all other situation, must use fields  Cannot add, multiply, compare struct variables  For any legal use, individual fields always available  Arrays of struct s can also be declared  Within the array, each entry is struct variable

18. Is It Legal? struct momentum { double mass, velocityX, velocityY; }; momentum bigMo; struct momentum car, truck; struct momentum van; van = 34; truck = {12, 34, 465.23}; car.mass = 22; truck.mass = car.mass * 34; cout << van << " " << car.velocityY << endl; car.velocityX -= pow(truck.mass, 2); van = sin(car); van.velocityX = car.velocityY + truck.velocityX;

19. Is It Legal? struct momentum { double mass, velocityX, velocityY; }; momentum bigMo; struct momentum car, truck; struct momentum van; van = 34; truck = {12, 34, 465.23}; car.mass = 22; truck.mass = car.mass * 34; cout << van << " " << car.velocityY << endl; car.velocityX -= pow(truck.mass, 2); van = sin(car); van.velocityX = car.velocityY + truck.velocityX;

20. Is It Legal? struct momentum { double mass, velocityX, velocityY; }; momentum bigMo; struct momentum car, truck; struct momentum van; van = 34; truck = {12, 34, 465.23}; car.mass = 22; truck.mass = car.mass * 34; cout << van << " " << car.velocityY << endl; car.velocityX -= pow(truck.mass, 2); van = sin(car); van.velocityX = car.velocityY + truck.velocityX;

21. Is It Legal? struct momentum { double mass, velocityX, velocityY; }; momentum bigMo; struct momentum car, truck; struct momentum van; van = 34; truck = {12, 34, 465.23}; car.mass = 22; truck.mass = car.mass * 34; cout << van << " " << car.velocityY << endl; car.velocityX -= pow(truck.mass, 2); van = sin(car); van.velocityX = car.velocityY + truck.velocityX;

22. Is It Legal? struct momentum { double mass, velocityX, velocityY; }; momentum bigMo; struct momentum car, truck; struct momentum van; van = 34; truck = {12, 34, 465.23}; car.mass = 22; truck.mass = car.mass * 34; cout << van << " " << car.velocityY << endl; car.velocityX -= pow(truck.mass, 2); van = sin(car); van.velocityX = car.velocityY + truck.velocityX;

23. Is It Legal? struct momentum { double mass, velocityX, velocityY; }; momentum bigMo; struct momentum car, truck; struct momentum van; van = 34; truck = {12, 34, 465.23}; car.mass = 22; truck.mass = car.mass * 34; cout << van << " " << car.velocityY << endl; car.velocityX -= pow(truck.mass, 2); van = sin(car); van.velocityX = car.velocityY + truck.velocityX;

24. Is It Legal? struct momentum { double mass, velocityX, velocityY; }; momentum bigMo; struct momentum car, truck; struct momentum van; van = 34; truck = {12, 34, 465.23}; car.mass = 22; truck.mass = car.mass * 34; cout << van << " " << car.velocityY << endl; car.velocityX -= pow(truck.mass, 2); van = sin(car); van.velocityX = car.velocityY + truck.velocityX;

25. Is It Legal? struct momentum { double mass, velocityX, velocityY; }; momentum bigMo; struct momentum car, truck; struct momentum van; van = 34; truck = {12, 34, 465.23}; car.mass = 22; truck.mass = car.mass * 34; cout << van << " " << car.velocityY << endl; car.velocityX -= pow(truck.mass, 2); van = sin(car); van.velocityX = car.velocityY + truck.velocityX;

26. Is It Legal? struct momentum { double mass, velocityX, velocityY; }; momentum bigMo; struct momentum car, truck; struct momentum van; van = 34; truck = {12, 34, 465.23}; car.mass = 22; truck.mass = car.mass * 34; cout << van << " " << car.velocityY << endl; car.velocityX -= pow(truck.mass, 2); van = sin(car); van.velocityX = car.velocityY + truck.velocityX;

27. Is It Legal? struct momentum { double mass, velocityX, velocityY; }; momentum bigMo; struct momentum car, truck; struct momentum van; van = 34; truck = {12, 34, 465.23}; car.mass = 22; truck.mass = car.mass * 34; cout << van << " " << car.velocityY << endl; car.velocityX -= pow(truck.mass, 2); van = sin(car); van.velocityX = car.velocityY + truck.velocityX;

28. Is It Legal? struct momentum { double mass, velocityX, velocityY; }; momentum bigMo; struct momentum car, truck; struct momentum van; van = 34; truck = {12, 34, 465.23}; car.mass = 22; truck.mass = car.mass * 34; cout << van << " " << car.velocityY << endl; car.velocityX -= pow(truck.mass, 2); van = sin(car); van.velocityX = car.velocityY + truck.velocityX;

29. Is It Legal? struct momentum { double mass, velocityX, velocityY; }; momentum bigMo; struct momentum car, truck; struct momentum van; van = 34; truck = {12, 34, 465.23}; car.mass = 22; truck.mass = car.mass * 34; cout << van << " " << car.velocityY << endl; car.velocityX -= pow(truck.mass, 2); van = sin(car); van.velocityX = car.velocityY + truck.velocityX;

30. Is It Legal? struct momentum { double mass, velocityX, velocityY; }; momentum bigMo; struct momentum car, truck; struct momentum van; van = 34; truck = {12, 34, 465.23}; car.mass = 22; truck.mass = car.mass * 34; cout << van << " " << car.velocityY << endl; car.velocityX -= pow(truck.mass, 2); van = sin(car); van.velocityX = car.velocityY + truck.velocityX;

31. Ooohhh… tracing colors struct color { int red, green, blue; }; int main(void) { struct color paints[2]; struct color pantone; paints[0].red = 128; paints[0].blue = 0; paints[0].green = paints[0].blue * 2; paints[1].red = 0; paints[1].blue = paints[0].red; paints[1].green = (paints[0].green+paints[1].blue); paints[1].blue = 0; paints[0].red = 0; pantone = paints[1];

32. Your Turn  Get into your groups and try this assignment

33. For Next Lecture  Mix pointers & struct s in 13.3  How do we get address of a struct for pointer?  Anything need to change to use field with pointer?  How can we create arrays of struct s dynamically?  Angel has Weekly Assignment #12 for tomorrow  Last programming assignment  Last programming assignment available now