Transcript C++ Basics - Cedarville University

C++ Basics
Compilation
 What does compilation do?
 g++ hello.cpp
 g++ -o hello.cpp hello
Comments
 Why we need comments
 Two styles
1. /*…………………..*/
2. //
C++ Variable
 Variables are the objects in C++ .where data is
stored, manipulated through expressions, and
printed. Variables have two defining
characteriestics: a name (or identifier) and a type.
C++ Variable Name Rules
 Variable names may only consist of alpha-numeric characters and
the '_' character.
 Variables names must begin with an alphabetic character or the '_'
character.
 Capitalization is meaningful. Therefore, myVar and MyVar are two
distinct variables.
 Variables may not have the same name as a C++ keyword.
some keywords: main, return, class, int, float, …
Variable Types
 There are an infinite number of allowable variable types, because C++ allows
programmers to define their own types. However, there are only a few built-in
types (i.e., types that are always available in C++ without any inclusions). The
built-in types are:
int - variables of this type store positive, zero, and negative integer values.
Float, double - variables of this type store values containing fractional or real
values.
char - variables of this type store single characters (e.g., 'a', 'F', '$', or '!').
bool - variables of this types store one of two values: true or false.
 There is one other type, string,which we will use frequently. The
string type is not built-in. You must include the string system
definitions to get this type (i.e., have the code #include <string>
appearing at the top of your program. The final type we will
frequently use is:
string - variables of this type store zero or more characters (e.g., "a string" or "hello").
Variable Declaration
 Before you can store information in a variable, it needs to be decalred.
When you declare a variable, you are identifying the variables two
defining characteristics, i.e., its name and its type. See below for
some sample variable declarations.
 Example:
int i;
// declares the integer variable called "i"
int myVar = 2; // declares the variable "myVar" and stores the number 2 into it
double x = 1.1; // declares the double variable "x" and stores a 1.1 into it
char c = 'Y'; // declares the variable "c" and stores a capital 'Y' into it
char midInitial; // declares a character variable without giving it a value
bool go = true; // declares a boolean (i.e., true/false) variable and sets it to true
string n = "Ed";// declares a string variable with the value "Ed" stored in it
Assignment
 we can put a value in the variable using the "=" operator. The value is
assigned from the right to the left.
 Example:
x = 10;
// store the value 10 in x
x = 10 + 4; // store the sum of 10 and 4 (that is 14) in x
x = x - 1; // this says take whatever is stored in x, subtract one from it, and store the
result back in x
x = 2 * y - z; // assumes you have the variables "y" and "z" already declared elsewhere in
your program
C++ I/O
 Output Statements
 To print out text or variables to the screen, we use a cout
statement, for example
 cout << "hello\n"; // this line prints the word hello to the
screen
 cout << x << endl; // this line prints the value of the variable
x to the screen
 Input Statements
 To enter a variable value into the program, we use a cin statement, for
example cin >> x;
// this line puts the value the user types in
the variable x
 cin >> x >> y; // input values in two variables x and y
Expression and Operators
 Syntax: variable = expr;
 expr is an expression made up of variables and operators (e.g., +, -,
*, /)