CPS120: Introduction to Computer Science

CPS120: Introduction to Computer Science Data Structures

Pointer Use in C++. • A pointer is a variable or constant that holds a memory address • a) Hexadecimal numbers are used for representing memory locations 216793 216794 216801 iptr … 216801 3 i 216802

Using Pointers • Pointers must be initialized • e.g. iptr =&I; • This reads iptr is assigned the address of i

Intializing Pointers • Declare pointers before use, as with other variables. • Each variable being declared as a pointer must be preceded by an asterisk (*). • Initialize pointers before use to a 0, NULL or an address to prevent unexpected results

Pointer Operators • & is the address operator which returns the address of its operand • * is the indirection operator or dereferencing operator and returns the value to which the operand (pointer) points.

Using enum • enum allows you to create your own simple data types for special purposes • Create a type • Give it a name • Specify values that are acceptable enum sizes {small, medium, large, jumbo}; • The compiler assigns an integer to each enum item

typedef • typedef gives a new name to an existing data type typedef float real; • Confusing to the reader, should be used sparingly

Structures • Structures group variables together in order to make one's programming task more efficient. • Any combination of variables can be combined into one structure. • This is a useful and efficient way to store data. struct Student { string socSecNum; string lastName; string firstName; int pointsEarned; double gpa; };

Using Structures • Each of the different variables are called members of the structure • Structures allow us to keep related data referring to individual members together • Strings, integer, and floating-point variables may be grouped together into one structure. • In effect, we have created our own customized data type. • The semicolon after the closing curly brace is required

Using the new data structure • The structure definition should be placed above the main function of a program but below the compiler directives • Declare an actual variable of this programmer-created data type within a function (such as main) in order to make use of this structureDone with a declaration statement like Student freshmen; • This reates a variable called freshmen of the data type Student

Assigning values to the structure • To assign a grade point average (GPA) of 3.4 to the gpa member of the variable freshmen, use the statement: freshmen.gpa = 3.4; • The period (.) that is used between the variable name freshmen and the member gpa is called the dot operator. • The dot operator simply us to reference individual members of a structure

Nested Structures • You can use a previously defined structure as a member of another structure • Address is nested inside of the Customer structure. • Since Address is used within Customer, the structure definition for Address must be placed above Customer in order to avoid compile errors struct Address{ string street; string city; string state; int zip;}; struct Customer{ string name; string phone; Address homeAddress; Address businessAddress; };

Classes • The definition of an object is know as a class • It is similar to using basic data structures in C++ • When you declare an object, you are said to have instantiated it (given it instances) • Objects are members of a class • Paul Millis, George Bush and George Washington being members of the human being class • The design of a class is as important as its implementation

CPS120: Introduction to Computer Science