EEE 243B Applied Computer Programming

1. EEE 243BApplied Computer Programming Structures §12.3

2. Review • What is the syntax for defining a type? • The enumerated type is built on which other type? • What is the value of each of the following? enum days {SUN, MON=-2, TUE, WED, THU, FRI, SAT}; • How would I change the above enumerated type to define a new type called DAYS? Prof S.P. Leblanc

3. Outline • Structures – Definition and Declaration • Tagged • Typedef • Structures - Initialization • Structures –Fields • Structures and pointers • Dynamic memory allocation Prof S.P. Leblanc

4. Structures • If we only used standard types in our programs, they would be very large, and difficult to maintain. • A structure is a collection of related elements, (called fields), possibly of different types having a single name Prof S.P. Leblanc

5. 1.Structure • If I want to describe my abstraction of a student I could collect the following info: • First name • Last name • College Number • Average • We can create a structure and declare a variable to store this information • This is similar to classes and class members • There are two different ways to declare a structure in C: • Tagged Structure • Type Declaration with typedef Prof S.P. Leblanc

6. 1a. Tagged Structure Definition • Here we show a tagged structure; • struct STUDENT • { • char firstName[15]; • char lastName[25]; • char collegeNumber[6]; • float average; • }; Prof S.P. Leblanc

7. 1a. Tagged Structures Declaration • To declare a variable for this structure, the struct keyword is repeated roughly the same as enum was for enumerated types: struct STUDENT aMilColStudent; Prof S.P. Leblanc

8. 1b. typedef Structures • Similar to enumerated types, typedef may be used to avoid the requirement to repeat the struct keyword with each declaration: • For most applications, you should use type-defined structures, as they are preferable: • typedefstruct • { • char firstName[15]; • char lastName[25]; • char collegeNumber[6]; • float average; • }STUDENT; //name of the type • STUDENT aMilColStudent; //Declare a variable Prof S.P. Leblanc

9. 2. Structure - initialization • Structures are initialised similarly to arrays. If we take the typedefSTUDENT and the variable aMilColStudentfrom the previous slide: STUDENT aMilColStudent = {"Joe", "Shmoe","45239",78.3}; You will have to come back much later to meet this OCdt Prof S.P. Leblanc

10. Example • Define a typedefstructure for a car, include • the manufacturer, • model name, • transmission type (manual or automatic), • number of doors (2 , 3 , 4 or 5), • colour, (Green, Beige, Grey, Black) • year, • engine size (in # cylinders) • The types from last class can be used in the structure Prof S.P. Leblanc

11. Example • Using the type just declared, declare a VEHICLE_TYPE variable for Manufacturer Chrysler Model Cordoba Year 1978 Doors 2 Cylinders 8 COLOURBLACK TRANSMISSION MANUAL Prof S.P. Leblanc

12. Solution (1) typedefenum {MANUAL, AUTOMATIC} TRANSMISSION ; typedefenum { RED, WHITE, YELLOW, GREEN, BEIGE, GREY, BLACK} COLOUR; typedefenum { 2=2, 3, 4, 5} DOORS; Prof S.P. Leblanc

13. Solution (2) typedefstruct { char manufacturer[25]; char model[25]; intyear; DOORS numDoors; TRANSMISSION transType; COLOUR carColour; intnumCylinders; } CAR; Prof S.P. Leblanc

14. Solution (3) CAR myFirstCar = { "CHRYSLER", "CORDOBA", 1978, 2, MANUAL, BLACK, 8 }; Prof S.P. Leblanc

15. 3.Structures and fields • Structures are constructed with fields. Everywhere you can use a variable you can use a structure field • Each field can be accessed individually with the structure member operator • (the period) . strcpy(aMilColStudent.firstName, "Bob"); aMilColStudent.collegeNumber = "98876"; You may meet this OCdt some day… Prof S.P. Leblanc

16. 3. Structures Operators, = • Structures are entities that can be treated as a whole, but ONLY during an assignment operation: STUDENT fStudent = {"Jane", "Doe", {'2','3','4','9','8'}, 33.2}; //poor Jane! aMilColStudent = fStudent; • You cannot compare two structures: if (aMilColStudent == fStudent) printf("Totally an error"); Prof S.P. Leblanc

17. 3. Structures and fields • In order to compare structures of the same type, you would need to write a function that compares each field in order: … //function returns 1 if all the field are equal intCompareStudents(STUDENT st1, STUDENT st2) { return ( !strcmp (st1.firstName,st2.firstName) && !strcmp (st1.lastName,st2.lastName) && !strcmp (st1.collegeNumber, st2.collegeNumber) && (fabs(st1.average - st2.average < 0.0001)) ); } Prof S.P. Leblanc

18. 4. Structures and Pointers • Like any other type in C, pointers can point to structures. The pointer points to the first byte of the structure. • You can also use pointers to access fields: STUDENT* pStudent= &aMilColStudent; aMilColStudent.collegeNumber = "12345"; (* pStudent).collegeNumber = "12345"; • Result is the same; but we need the brackets around the dereferencing due to precedence Prof S.P. Leblanc

19. 4. Structures and Pointers • Fortunately C provides another operator that allows us to dereference the pointer and access the field at the same time; the structure selection operator: pStudent->collegeNumber = "54321"; Prof S.P. Leblanc

20. 5. Dynamic memory allocation • Recall that we can allocate memory dynamically • You can also allocate memory for any types including typedef'd structures: typedefstruct { char firstName[15]; char lastName[25]; } NAME; NAME *pName = NULL; pName = (NAME *)malloc (sizeof(NAME)); Prof S.P. Leblanc

21. Quiz Time • What is printed in the following code? int* pInt; STUDENT aStudent={"Jane", "Doe", "23498", 33.2}; STUDENT* pStudent= &aStudent; pInt= &aStudent.collegeNumber; printf("%s \’s student Number is %ld", (*pStudent).firstName, *pInt); printf("%s \’s student Number is %ld", pStudent->firstName, aStudent.collegeNumber); Prof S.P. Leblanc

22. Quiz Time • If you declare a variable that is a type-defined structure what operator do you use to access its fields? • If you have a pointer that points to a structure, what operator do you use to access each field? • Can you assign a complete structure to another? • Can you compare structures with == ? Prof S.P. Leblanc

23. Next lecture • Linked List I Prof S.P. Leblanc