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Saturday, February 3, 2007

Saturday, February 3, 2007. “Programmer - an organism that turns coffee into software.” - Anonymous. struct for representing roll_no , name and marks for student. Pointers to arrays of structures struct Rect{ int x; int y; int width; int height; }; int main(void){ int size;

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Saturday, February 3, 2007

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  1. Saturday, February 3, 2007 “Programmer - an organism that turns coffee into software.” - Anonymous

  2. struct for representing roll_no, name and marks for student

  3. Pointers to arrays of structures struct Rect{ int x; int y; int width; int height; }; int main(void){ int size; cin>>size; Rect* rectArray=new Rect[size]; rectArray[0].x=10; rectArray[0].y=20; rectArray[0].width=50; rectArray[0].height=100; // and so-on return 0; }

  4. const int size=5; Rect rect[size]={ {10,10, 20,30}, {15,15, 25,40}, {8, 10, 80, 50}, {60, 0, 50, 50}, {0, 20, 60, 10} }; int i; for (i=0; i<size; i++){ cout<<rect[i].x<<" "<<rect[i].y<<" " <<rect[i].width<<" "<<rect[i].height<<endl; }

  5. numerator 7 f1 22 denominator fraction * struct fraction { int numerator; int denominator; }; // Don't forget the semicolon! fraction* f1=new fraction; Expression Type f1 fraction* *f1 fraction (*f1).numerator int //parenthesis important f1->numerator int

  6. struct Location{ char *address; int zipcode; }; struct Course{ char title[20]; int num_students; Location loc; }; int i; Course courses[10]; for (i=0; i<10; i++){ //______________? } Course* coursePtr; coursePtr=new Course; //_________________? cout<<___________________<<endl; return 0; } How to set num_students to some value in both cases?

  7. struct Location{ char *address; int zipcode; }; struct Course{ char title[20]; int num_students; Location loc; }; int i; Course courses[10]; for (i=0; i<10; i++){ courses[i].num_students=60; } Course* coursePtr; coursePtr=new Course; coursePtr->num_students=35; cout<<coursePtr->num_students<<endl; return 0; }

  8. Structures within Structures struct addr { char name[40]; char street[40]; char city[40]; int zip; }; struct emp { addr address; float wage; } ; emp worker; How to set zip code to 12345?

  9. Structures within Structures struct addr { char name[40]; char street[40]; char city[40]; int zip; }; struct emp { addr address; float wage; } worker; worker.address.zip = 12345;

  10. Structures within Structures struct addr { char name[40]; char street[40]; char city[40]; int zip; }; struct emp { addr *address; float wage; }; emp worker; How to set zip code to 12345?

  11. Structures within Structures struct addr { char name[40]; char street[40]; char city[40]; int zip; }; struct emp { addr *address; float wage; }; int main(void){ emp worker; worker.address=new addr; worker.address->zip=12345; cout<<worker.address->zip; return 0; }

  12. What if we had declared a pointer to emp? emp * worker;

  13. struct Location{ char *address; int zipcode; }; struct Course{ char title[20]; int num_students; Location loc; }; SELF TEST: Fill out all members of the nested struct with values

  14. int main(){ Course cs192; strcpy(cs192.title, "Problem Solving"); cs192.num_students=65; cs192.loc.zipcode=54890; cs192.loc.address = new char[20]; strcpy(cs192.loc.address, "LUMS"); cout<<cs192.loc.address<<endl; ... } SELF TEST

  15. struct Turbine{ char *location; long rating; int num_cylinders; double weight; Motor motor; }; struct Fan{ char *manufacturer; double blade_length; double temp_rating; double pressure_rating; }; struct Motor{ char * manufacturer; double watts; double speed; int num_phases; Fan fan; };

  16. Turbine steamTurbine; steamTurbine.location=new char[20]; strcpy(steamTurbine.location, "Tarbela Dam"); steamTurbine.rating=15000; struct Fan{ char *manufacturer; double blade_length; double temp_rating; double pressure_rating; }; struct Motor{ char * manufacturer; double watts; double speed; int num_phases; Fan fan; }; struct Turbine{ char *location; long rating; int num_cylinders; double weight; Motor motor; };

  17. Turbine steamTurbine; steamTurbine.location=new char[20]; strcpy(steamTurbine.location, "Tarbela Dam"); steamTurbine.rating=15000; steamTurbine.motor.manufacturer=new char[20]; strcpy(steamTurbine.motor.manufacturer, "Mitsubishi"); steamTurbine.motor.num_phases=3; struct Fan{ char *manufacturer; double blade_length; double temp_rating; double pressure_rating; }; struct Motor{ char * manufacturer; double watts; double speed; int num_phases; Fan fan; }; struct Turbine{ char *location; long rating; int num_cylinders; double weight; Motor motor; };

  18. Turbine steamTurbine; steamTurbine.location=new char[20]; strcpy(steamTurbine.location, "Tarbela Dam"); steamTurbine.rating=15000; steamTurbine.motor.manufacturer=new char[20]; strcpy(steamTurbine.motor.manufacturer, "Mitsubishi"); steamTurbine.motor.num_phases=3; steamTurbine.motor.fan.blade_length=100; steamTurbine.motor.fan.temp_rating=300; //etc... cout<<steamTurbine.motor.manufacturer<<endl; cout<<steamTurbine.motor.fan.temp_rating<<endl; struct Fan{ char *manufacturer; double blade_length; double temp_rating; double pressure_rating; }; struct Motor{ char * manufacturer; double watts; double speed; int num_phases; Fan fan; }; struct Turbine{ char *location; long rating; int num_cylinders; double weight; Motor motor; };

  19. What should change here? Turbine steamTurbine; steamTurbine.location=new char[20]; strcpy(steamTurbine.location, "Tarbela Dam"); steamTurbine.rating=15000; steamTurbine.motor.manufacturer=new char[20]; strcpy(steamTurbine.motor.manufacturer, "Mitsubishi"); steamTurbine.motor.num_phases=3; steamTurbine.motor.fan.blade_length=100; steamTurbine.motor.fan.temp_rating=300; //etc... cout<<steamTurbine.motor.manufacturer<<endl; cout<<steamTurbine.motor.fan.temp_rating<<endl; struct Fan{ char *manufacturer; double blade_length; double temp_rating; double pressure_rating; }; struct Motor{ char * manufacturer; double watts; double speed; int num_phases; Fan *fan; }; struct Turbine{ char *location; long rating; int num_cylinders; double weight; Motor motor; };

  20. Turbine steamTurbine; steamTurbine.location=new char[20]; strcpy(steamTurbine.location, "Tarbela Dam"); steamTurbine.rating=15000; steamTurbine.motor.manufacturer=new char[20]; strcpy(steamTurbine.motor.manufacturer, "Mitsubishi"); steamTurbine.motor.num_phases=3; steamTurbine.motor.fan = new Fan; steamTurbine.motor.fan->blade_length=100; steamTurbine.motor.fan->temp_rating=300; //etc... cout<<steamTurbine.motor.manufacturer<<endl; cout<<steamTurbine.motor.fan->temp_rating<<endl; struct Fan{ char *manufacturer; double blade_length; double temp_rating; double pressure_rating; }; struct Motor{ char * manufacturer; double watts; double speed; int num_phases; Fan *fan; }; struct Turbine{ char *location; long rating; int num_cylinders; double weight; Motor motor; };

  21. Structures (Inventory Example) const int SIZE = 100; struct inv_type { char item[40]; // name of item double cost; // cost double retail; // retail price int on_hand; // amount on hand int lead_time; // number of days before resupply }; inv_type invtry[SIZE]; READ THE BOOK!

  22. int main() { char choice; init_list(); for(;;) { choice = menu(); switch(choice) { case 'e': enter(); break; case 'd': display(); break; case 'u': update(); break; case 'q': return 0; } } }

  23. Structures (Inventory Example) // Initialize the inv_type_info array. void init_list() { int t; // a zero length name signifies empty for(t=0; t<SIZE; t++) *(invtry[t].item) = '\0'; }

  24. Structures (Inventory Example) // Get a menu selection. int menu(){ char ch; cout << '\n'; do { cout << "(E)nter\n"; cout << "(D)isplay\n"; cout << "(U)pdate\n"; cout << "(Q)uit\n\n"; cout << "choose one: "; cin >> ch; } while(!strchr("eduq", tolower(ch))); return tolower(ch); } #include <string.h> strchr locates character in string 

  25. Structures (Inventory Example) // Enter items into the list. void enter(){ int i; // find the first free structure for(i=0; i<SIZE; i++) if(!*(invtry[i].item)) break; // i will equal SIZE if the list is full if(i==SIZE) { cout << "List full.\n"; return; } input(i); }

  26. Structures (Inventory Example) // Input the information. void input(int i){ char str[80]; // enter the information cout << "Item: "; cin >> invtry[i].item; cout << "Cost: "; cin >> invtry[i].cost; cout << "Retail price: "; cin >> invtry[i].retail; cout << "On hand: "; cin >> invtry[i].on_hand; cout << "Lead time to resupply (in days): "; cin >> invtry[i].lead_time; }

  27. Structures (Inventory Example) // Modify an existing item. void update(){ int i; char name[80]; cout << "Enter item: "; cin >> name; for(i=0; i<SIZE; i++) if(!strcmp(name, invtry[i].item)) break; if(i==SIZE) { cout << "Item not found.\n"; return; } cout << "Enter new information.\n"; input(i); }

  28. Structures (Inventory Example) // Display the list. void display(){ int t; for(t=0; t<SIZE; t++) { if(*(invtry[t].item)) { cout << invtry[t].item << '\n'; cout << "Cost: $" << invtry[t].cost; cout << "\nRetail: $"; cout << invtry[t].retail << '\n'; cout << "On hand: "<< invtry[t].on_hand; cout << "\nResupply time: "; cout<<invtry[t].lead_time<< " days\n\n"; } } }

  29. Arrays VS. linked lists? int scores[100]; The disadvantages of arrays are... • The size of the array is fixed — 100 elements in this case. Most often this size is specified at compile time with a simple declaration such as in the example above. • With a little extra effort, the size of the array can be deferred until the array is created at runtime, but after that it remains fixed.

  30. Arrays VS. linked lists? • Because of this, the most convenient thing for programmers to do is to allocate arrays which seem "large enough" (e.g. the 100 in the scores example) • Although convenient, this strategy has two disadvantages: (a) most of the time there are just 20 or 30 elements in the array and 70% of the space in the array really is wasted. (b) If the program ever needs to process more than 100 scores, the code breaks.

  31. Arrays VS. linked lists? • Inserting new elements at the front of array is potentially expensive because existing elements need to be shifted over to make room. • Merging, Deleting ... • Example of queues

  32. LINKED LISTS • Linked lists store collections of data • A linked list is a list constructed using pointers • A linked list is not fixed in size but can grow and shrink while your program is running.

  33. What Linked Lists Look Like? • An array allocates memory for all its elements lumped together as one block of memory. • In contrast, a linked list allocates space for each element separately in its own block of memory called a "linked list element" or "node". • The list gets is overall structure by using pointers to connect all its nodes together like the links in a chain.

  34. What Linked Lists Look Like? • Each node contains two fields: a "data" field to store whatever element type the list holds and a "next" field which is a pointer used to link one node to the next node. • Example … • The Empty List — NULL

  35. Linked Lists struct node { int data; node* next; };

  36. Linked Lists - easy example first . . . second->next = third; third->data = 3; third->next = NULL; return head; } /*Build the list {1, 2, 3}*/ node* BuildOneTwoThree() { node* head = NULL; node* second = NULL; node* third = NULL; head = new node; second = new node; third = new node; head->data = 1; head->next = second; second->data = 2;

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