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; )