Overview of Structs in C Programming: Initialization, Usage, and Combining Structs

1. HKUST SummerProgramming Course 2008 Structure

2. Overview • Structure • Initialize a struct • Quiz • Semicolon in a struct definition • Combining structs

3. Struct • A collection of values of different types (a structure) struct FruitCollection { int quantity; char size; // (L)arege, (M)iddle and (S)mall }; • Usually be placed under global scope, it can also be put in another scopes. • Use dot operator (.) to access member variables. FruitCollection pineapple; pineapple.quantity = 6; pineapple.size = ‘L’; • Can have more than one struct in a single program

4. Initialize a struct • Initialize by a list of values according to the sequence of variables in the struct definition. FruitCollection orange = { 100, ‘M’ }; • If number of values is MORE than the struct requires, error will occur. • If number of values is LESS than the struct requires, zero value will be given to the rest of variables. • In contrast, C++ won’t initialize local variables • Copy from other objects of the same type. FruitCollection apple; apple = orange; //apple is now {100, ‘M’}

5. Quiz int main() { struct Date{ int month, day, year; } Date dueDate = { 31, 12, 2006 }; return 0; } • What’s wrong with the program?

6. Semicolon in a struct definition • A semicolon must be put at the end of a struct definition, otherwise the program can’t compile. struct Date { int month, day, year; }; //<- remember to add this semicolon • A useful feature related to this semicolon. struct fruit { int quantity; char size; } apple, orange; // variables of fruit type • Variables of this struct can be declared immediately after the definition.

7. Logical error • The order of initialization of data member is the same as the order of declaration of data member • The previous example will initialize the date as Year = 2006, Month = 31, Day = 12

8. Combining structs • A struct can make use of another struct to be the type of its member variables. // fruitCollection was defined in previous slides struct fruitBasket { fruitCollection apple; fruitCollection orange; }; int main() { fruitBasket A; A.apple.quantity = 3; A.apple.size = ‘L’; A.orange.quantity = 6; … } • To access the member variable of a struct inside another struct, we can use the dot operator twice. (Dot operator also called member access operator)

9. Combining structs • A struct can also be defined inside another struct. struct bookBorrow { string borrower; string bookTitle; // struct inside another struct struct Date { int day, month, year; } dueDate; }; • Be careful when you try to initialize it, bookBorrow bk001={"Adam", "The Wizard Book", {31,12,2006}}; cout << bk001.dueDate.day << endl; // output is 31