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Introduction to C++ : Introduction to C++ Readings: 1.1-1.3, 1.9-1.13, 1.16-1.18, 1.21-1.22 C++ Bjarne Stroustrup (Bell Labs, 1979) started as extension to C (macros and variables) added new useful, features nowadays a language of its own C++ (the next thing after C, though wouldn’t ++C be more appropriate?)

Outline : Outline Intro to C++ Object-Oriented Programming Changes in C++ comments variable declaration location initialization pointer changes tagged structure type enum types bool type

Object-Oriented Programming : Object-Oriented Programming First-class objects - atomic types in C int, float, char have: values sets of operations that can be applied to them how represented irrelevant to how they are manipulated Other objects - structures in C cannot be printed do not have operations associated with them (at least, not directly)

Object-Oriented Idea : Object-Oriented Idea Make all objects, whether C-defined or user-defined, first-class objects For C++ structures (called classes) allow: functions to be associated with the class only allow certain functions to access the internals of the class allow the user to re-define existing functions (for example, input and output) to work on class

Classes of Objects in C++ : Classes of Objects in C++ Classes similar to structures in C (in fact, you can can still use the struct definition) have fields corresponding to fields of a structure in C (similar to variables) have fields corresponding to functions in C (functions that can be applied to that structure) some fields are accessible by everyone, some not (data hiding) some fields shared by the entire class

Instances of Classes in C++ : Instances of Classes in C++ A class in C++ is like a type in C Variables created of a particular class are instances of that class Variables have values for fields of the class Class example: Student has name, id, gpa, etc. fields that store values has functions, changeGPA, addCredits, that can be applied to instances of that class Instance examples: John Doe, Jane Doe each with their own values for the fields of the class

Comments in C++ : Comments in C++ Can use C form of comments /* A Comment */ Can also use // form: when // encountered, remainder of line ignored works only on that line Examples: void main() { int I; // Variable used in loops char C; // No comment comment

Variable Declarations : Variable Declarations In C++, variable declarations are not restricted to the beginnings of blocks (before any code) you may interleave declarations/statements as needed it is still good style to have declarations first Example void main() { int I = 5; printf(“Please enter J: “); int J; // Not declared at the start scanf(“%d”,&J);

Counter Variables in a For Loop : Counter Variables in a For Loop You can declare the variable(s) used in a for loop in the initialization section of the for loop good when counter used in for loop only exists in for loop (variable is throw-away) Example for (int I = 0; I < 5; I++) printf(“%d\n”,I); Variable exists only during for loop (goes away when loop ends)

Initializing Global Variables : Initializing Global Variables Not restricted to using constant literal values in initializing global variables, can use any evaluable expression Example: int rows = 5; int cols = 6; int size = rows * cols; void main() { ...

Initializing Array Elements : Initializing Array Elements When giving a list of initial array values in C++, you can use expressions that have to be evaluated Values calculated at run-time before initialization done Example: void main() { int n1, n2, n3; int *nptr[] = { &n1, &n2, &n3 };

void* : void* In C it is legal to cast other pointers to and from a void * In C++ this is an error, to cast you should use an explicit casting command Example: int N; int *P = &N; void *Q = P; // illegal in C++ void *R = (void *) P; // ok

NULL in C++ : NULL in C++ C++ does not use the value NULL, instead NULL is always 0 in C++, so we simply use 0 Example: int *P = 0; // equivalent to // setting P to NULL Can check for a 0 pointer as if true/false: if (!P) // P is 0 (NULL) ... else // P is not 0 (non-NULL) ...

Tags and struct : Tags and struct When using struct command in C++ (and for other tagged types), can create type using tag format and not use tag in variable declaration: struct MyType { int A; float B; }; MyType V;

enum in C++ : enum in C++ Enumerated types not directly represented as integers in C++ certain operations that are legal in C do not work in C++ Example: void main() { enum Color { red, blue, green }; Color c = red; c = blue; c = 1; // Error in C++ ++c; // Error in C++

bool : bool C has no explicit type for true/false values C++ introduces type bool (later versions of C++) also adds two new bool literal constants true (1) and false (0) Other integral types (int, char, etc.) are implicitly converted to bool when appropriate non-zero values are converted to true zero values are converted to false

bool operations : bool operations Operators requiring bool value(s) and producing a bool value: && (And), || (Or), ! (Not) Relational operators (==, !=, <, >, <=, >=) produce bool values Some statements expect expressions that produce bool values: if (boolean_expression) while (boolean_expression) do … while (boolean_expression) for ( ; boolean_expression; )