chap11 Chapter 11 Structure and Union Types

chap11 2 Objectives We have seen how to represent numbers, characters, words, other strings, and lists (arrays) of these objects. We will show how to broaden the modeling facilities of C by defining our own data types that represent structured collections of data pertaining to particular objects.

chap11 3 User-Defined Structure Types A database is a collection of information subdivided into records. A record is a collection of information of one data object (e.g., ID, name, and age of a student). C allows us to define a new data type (called structure type) for each category of a structured data object.

chap11 4 Declaring Structure Types Syntax typedef struct struct_type typedef struct{ type1 id1; type2 id2; … } struct_type; typedef struct student_info; example typedef struct{ char[20] name; int age; } student_info;

chap11 5 Declaring Structure Types Declaration: student_info student1, student2 = {“Wang”, 18}; A hierarchical structure is a structure containing components which are also structures. typedef struct{ int NumOfStudents; student_info students[20]; } class_info;

chap11 6 Manipulating Individual Components of a Structured Data Type direct component selection operator We can reference a component of a structure by the direct component selection operator, which is a period. E.g., strcpy(student1.name, “Wang”); student1.age = 18; printf(“%s is in age %d\n”, student1.name, student1.age);

chap11 7 Manipulating Structures The direct component selection operator has the highest priority in the operator precedence. student1.age+student2.age+…; The value of student1.age is referenced first. The copy of an entire structure can be easily done by the assignment operator. student1 = student2; Each component in one structure is copied into the corresponding component in the other structure.

chap11 8 Structure Type Data as Input & Output Parameters As an input argument: all of its component values are copied into the components of the function ’ s corresponding formal parameter. As an output argument: the address-of operator must be applied.

chap11 9 Function with a Structured Input Parameter Suppose there is a structure defined as follows. typedef struct{ char name[20]; double diameter; int moons; double orbit_time, rotation_time; } planet_t;

chap11 10 Function with a Structured Input Parameter When a structure variable is passed as an input argument to a function, all its component values are copied into the local structure variable.

chap11 11 Comparing Two Structured Values for Equality The equality and inequality operators cannot be applied to a structured type as a unit.

chap11 12 Function with a Structured Input/Output Argument For the following function, we have to call it by “ scan_planet(&current_planet);” The input argument is also used to store the result. “ *plnp ” is parenthesized because & operator has higher precedence.

chap11 13 & Data Areas of call to scan_planet(&current_planet); plnp is a pointer which points to the same data area of current_planet.

chap11 14 Step-by-Step Analysis of the Indirect Reference

chap11 15 Indirect Component Selection Operator In the above example, we use direct component selection operator: period.. e.g., &(*plnp).diameter C also provides indirect component selection operator: -> - > &plnp - >diameter is the same as &(*plnp).diameter

chap11 16 Functions Whose Result are Structured

chap11 17 Example: Compute an Updated Time Value

chap11 18 Example: Compute an Updated Time Value

chap11 19 Problem Solving with Structure Types We must also provide basic operations for manipulating these structure types

chap11 20 Case Study: Complex Numbers (Fig ) A complex number is a number of a real part and an imaginary part. a+bi

chap11 21 Arrays of Structures We can also declare an array of structures. typedef struct{ int id; double gpa; } student_t; Usage: student_t stulist[50]; stulist[3].id = ; stulist[3].gpa = 3.0;

chap11 22 Arrays of Structures The array of structures can be simply manipulated as arrays of simple data types.

chap11 23 Case Study: Universal Measurement Conversion (Fig )

chap11 24 Union Types Union is a data structure which represents only one of the component in the declaration. typedef union{ int wears_wig; char color[20]; } hair_t; Suppose we declare a vairable “ hait_t hair_data; ”. This hair_data contains either the wears_wig component or the color component but not both.

chap11 25 Example Suppose we have a structure variable. typedef struct{ int bald; hair_t h; } hair_info_t We can use this structure to reference the correct component. Use the wears_wig component. Use the color component.

chap11 26 Two Interpretations of the Union Variable hair_t The memory content of hair_t depends on which component is referenced. The memory allocated for hair_t is determined by the largest component in the union. Referencing the correct union component is the programmer ’ s responsibility. The wears_wig component is referenced. The color component is referenced.