C++ Basics

1. C++ Basics

2. Compilation • What does compilation do? • g++ hello.cpp • g++ -o hello.cpp hello

3. Comments • Why we need comments • Two styles 1. /*…………………..*/ 2. //

4. 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.

5. 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, …

6. 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").

7. 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

8. 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

9. 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

10. Expression and Operators • Syntax:  variable = expr; • expr is an expression made up of variables and operators (e.g., +, -, *, /)