CPP loop

By Santosh Tawde

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?)

C++

By Santosh Tawde

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

• 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

• 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
• 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++

• 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++

• 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

• 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

• 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

• 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

• 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*

• 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++

• 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

• 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++

• 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

• 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

• 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; )