Discovr what is new in c++


           If you're looking for free tutorials, learn C++ with our C++ tutorial, starting at C++ Made Easy… This tutorial is for those people who want to learn programming in C++ and do not necessarily have any previous knowledge of other programming languages. Of course any knowledge of other programming languages or any general computer skill can be useful to better understand this tutorial, although it is not essential.It is also suitable for those who need a little update on the new features the language has acquired from the latest standards.

Getting Set Up - C++ Compilers
           The very first thing you need to do, before starting out in C++, is to make sure that you have a compiler. What is a compiler, you ask? A compiler turns the program that you write into an executable that your computer can actually understand and run. If you're taking a course, you probably have one provided through your school.
         If you're starting out on your own, your best bet is to use Code::Blocks with MinGW. If you're on Linux, you can use g++, and if you're on Mac OS X, you can use XCode. (If you are stuck using an older compiler, such as Turbo C++, you'll need to read this page on compatibility issues.) If you haven't yet done so, go ahead and get a compiler set up--you'll need it for the rest of the tutorial.

Introduction to the C++ Language
           A C++ program is a collection of commands, which tell the computer to do "something". This collection of commands is usually called C++ source code, source code or just code. Commands are either "functions" or "keywords". Keywords are a basic building block of the language, while functions are, in fact, usually written in terms of simpler functions--you'll see this in our very first program, below. Thankfully, C++ provides a great many common functions and keywords that you can use.
But how does a program actually start? Every program in C++ has one function, always named main, that is always called when your program first executes. From main, you can also call other functions whether they are written by us or, as mentioned earlier, provided by the compiler. So how do you get access to those prewritten functions? To access those standard functions that comes with the compiler, you include a header with the #include directive.What this does is effectively take everything in the header and paste it into your program. 
Let's look at a working program:

#include <iostream> 
Using namespace std;
int main()
  cout<<"HEY, you, I'm alive! Oh, and Hello World!\n";

Let's look at the elements of the program.

The #include is a "preprocessor" directive that tells the compiler to put code from the header called iostream into our program. Before actually creating the executable. By including header files, you gain access to many different functions.
For example, the cout function requires iostream. Following the include is the statement, "using namespace std;".This line tells the compiler to use a group of functions that are part of the standard library (std). By including this line at the top of a file, you allow the program to use functions such as cout. The semicolon is part of the syntax of C++. It tells the compiler that you're at the end of a command.
 You will see later that the semicolon is used to end most commands in C++. The next important line is int main (). This line tells the compiler that there is a function named main, and that the function returns an integer, hence int.
The "curly braces" ({and }) signal the beginning and end of functions and other code blocks. You can think of them as meaning BEGIN and END. The next line of the program may seem strange. If you have programmed in another language, you might expect that print would be the function used to display text. In C++, however, the cout object is used to display text (pronounced "C out").
 It uses the << symbols, known as "insertion operators", to indicate what to output. cout<< results in a function call with the ensuing text as an argument to the function. The quotes tell the compiler that you want to output the literal string as-is. The '\n' sequence is actually treated as a single character that stands for a newline (we'll talk about this later in more detail). It moves the cursor on your screen to the next line. Again, notice the semicolon: it is added onto the end of most lines, such as function calls, in C++. 
                 The next command is cin.get(). This is another function call: it reads in input and expects the user to hit the return key. Many compiler environments will open a new console window, run the program, and then close the window. This command keeps that window from closing because the program is not done yet because it waits for you to hit enter. Including that line gives you time to see the program run.
Upon reaching the end of main, the closing brace, our program will return the value of 0 (and integer, hence why we told main to return an int) to the operating system. This return value is important as it can be used to tell the OS whether our program succeeded or not. A return value of 0 means success and is returned automatically (but only for main, other functions require you to manually return a value), but if we wanted to return something else,

We would have to do it with a return statement:

 #include <iostream>
using namespace std;  
int main()
  cout<<"HEY, you, I'm alive! Oh, and Hello World!\n";
  return 1;

     The final brace closes off the function. You should try compiling this program and running it. You can cut and paste the code into a file, save it as a .cpp file. Our Code::Blocks tutorial actually takes you through creating a simple program, so check it out if you're confused.
If you are not using Code::Blocks, you should read the compiler instructions for information on how to compile. Once you've got your first program running, why don't you try playing around with the cout function to get used to writing C++?

An Aside on Commenting Your Programs
               As you are learning to program, you should also start to learn how to explain your programs (for yourself, if no one else). You do this by adding comments to code; I'll use them frequently to help explain code examples.
        When you tell the compiler a section of text is a comment, it will ignore it when running the code, allowing you to use any text you want to describe the real code. To create a comment use either //, which tells the compiler that the rest of the line is a comment, or /* and then */ to block off everything between as a comment.    Certain compiler environments will change the color of a commented area, but some will not. Be certain not to accidentally comment out code (that is, to tell the compiler part of your code is a comment) you need for the program. When you are learning to program, it is useful to be able to comment out sections of code in order to see how the output is affected.
User interaction and Saving Information with Variables
          So far you've learned how to write a simple program to display information typed in by you, the programmer, and how to describe your program with comments. That's great, but what about interacting with your user? Fortunately, it is also possible for your program to accept input.
The function you use is known as cin, and is followed by the insertion operator >>. Of course, before you try to receive input, you must have a place to store that input. In programming, input and data are stored in variables. There are several different types of variables which store different kinds of information
(e.g. numbers versus letters); when you tell the compiler you are declaring a variable, you must include the data type along with the name of the variable. Several basic types include char, int, and float.
A variable of type char stores a single character, variables of type int store integers (numbers without decimal places), and variables of type float store numbers with decimal places. Each of these variable types - char, int, and float - is each a keyword that you use when you declare a variable.
What's with all these variable types?
Sometimes it can be confusing to have multiple variable types when it seems like some variable types are redundant (why have integer numbers when you have floats?). Using the right variable type can be important for making your code readable and for efficiency--some variables require more memory than others. Moreover, because of the way the numbers are actually stored in memory, a float is "inexact", and should not be used when you need to store an "exact" integer value.

Declaring Variables in C++

                To declare a variable you use the syntax "type <name>;". Here are some variable declaration examples:

int x; 
char letter; 
float the_float; 

   It is permissible to declare multiple variables of the same type on the same line; each one should be separated by a comma. 
int a, b, c, d; 
If you were watching closely, you might have seen that declaration of a variable is always followed by a semicolon (note that this is the same procedure used when you call a function). 

Common Errors when Declaring Variables in C++

            If you attempt to use a variable that you have not declared, your program will not be compiled or run, and you will receive an error message informing you that you have made a mistake. Usually, this is called an undeclared variable. 

Case Sensitivity

             Now is a good time to talk about an important concept that can easily throw you off: case sensitivity. Basically, in C++, whether you use uppercase or lowercase letters matters. The words Cat and cat mean different things to the compiler. In C++, all language keywords, all functions and all variables are case sensitive. A difference in case between your variable declaration and the use of the variable is one reason you might get an undeclared variable error.
Using Variables

            Ok, so you now know how to tell the compiler about variables, but what about using them? Here is a sample program demonstrating the use of a variable:

#include <iostream> 
using namespace std; 
int main() 
  int thisisanumber; 
  cout<<"Please enter a number: "; 
  cin>> thisisanumber; 
  cout<<"You entered: "<< thisisanumber <<"\n"; 
Let's break apart this program and examine it line by line.
The keyword int declares this is a number to be an integer. The function cin>> reads a value into this is a number; the user must press enter before the number is read by the program.
 cin.ignore() is another function that reads and discards a character. Remember that when you type input into a program, it takes the enter key too. We don't need this, so we throw it away. Keep in mind that the variable was declared an integer; if the user attempts to type in a decimal number, it will be truncated (that is, the decimal component of the number will be ignored).

Try typing in a sequence of characters or a decimal number when you run the example program; the response will vary from input to input, but in no case is it particularly pretty. Notice that when printing out a variable quotation marks are not used. Were there quotation marks, the output would be "You Entered: this is a number." The lack of quotation marks informs the compiler that there is a variable, and therefore that the program should check the value of the variable in order to replace the variable name with the variable when executing the output function. 
Do not be confused by the inclusion of two separate insertion operators on one line. Including multiple insertion operators on one line is perfectly acceptable and all of the output will go to the same place. In fact, you must separate string literals (strings enclosed in quotation marks) and variables by giving each its own insertion operators (<<). Trying to put two variables together with only one << will give you an error message, do not try it. 
                 Do not forget to end functions and declarations with a semicolon. If you forget the semicolon, the compiler will give you an error message when you attempt to compile the program.

Changing and Comparing Variables

                Of course, no matter what type you use, variables are uninteresting without the ability to modify them. Several operators used with variables include the following: *, -, +, /, =, ==, >, <. The * multiplies, the - subtracts, and the + adds. It is of course important to realize that to modify the value of a variable inside the program it is rather important to use the equal sign. In some languages, the equal sign compares the value of the left and right values, but in C++ == is used for that task. 
The equal sign is still extremely useful. It sets the left input to the equal sign, which must be one, and only one, variable equal to the value on the right side of the equal sign. The operators that perform mathematical functions should be used on the right side of an equal sign in order to assign the result to a variable on the left side. Here are a few examples:

a = 4 * 6;// (Note use of comments and of semicolon) a is 24 
a = a + 5;//a equals the original value of a with five added to it 
a == 5// Does NOT assign five to a. Rather, it checks to see if a equals 5
The other form of equal, ==, is not a way to assign a value to a variable. Rather, it checks to see if the variables are equal. It is useful in other areas of C++; for example, you will often use == in such constructions as conditional statements and loops. You can probably guess how < and > function. They are greater than and less than operators. 
For example:

a < 5  // Checks to see if a is less than five 
a > 5  // Checks to see if a is greater than five 
a == 5 // Checks to see if a equals five, for good measure 
Comparing variables isn't really useful until you have some way of using the results--that's what lesson 2, on if statements is all about.

If you enjoyed this tutorial, check out some sample questions @ C++ Contest .plus much more? In one convenient place, along with tons of sample code and practice problems.
Quiz yourself @ C++  contest (NEW)

If you're having some trouble following the tutorial or program write me at fajarpm786@gmail.com.

 If statements in C++

              The ability to control the flow of your program, letting it make decisions on what code to execute, is valuable to the programmer. If statement allows you to control if a program enters a section of code or not based on whether a given condition is true or false. One of the important functions of the if statement is that it allows the program to select an action based upon the user's input.
 For example, by using an if statement to check a user entered password, your program can decide whether a user is allowed access to the program. 
Without a conditional statement such as the if statement, programs would run almost the exact same way every time. If statements allow the flow of the program to be changed , and so they allow algorithms and more interesting code. 
Before discussing the actual structure of the if statement, let us examine the meaning of TRUE and FALSE in computer terminology. A true statement is one that evaluates to a nonzero number. A false statement evaluates to zero.
When you perform comparison with the relational operators, the operator will return 1 if the comparison is true, or 0 if the comparison is false. For example, the check 0 == 2 evaluates to 0. The check 2 == 2 evaluates to a 1. 
If this confuses you, try to use a cout statement to output the result of those various comparisons (for example cout<< ( 2 == 1 );) When programming, the aim of the program will often require the checking of one value stored by a variable against another value to determine whether one is larger, smaller, or equal to the other. 
There are a number of operators that allow these checks. 
Here are the relational operators, as they are known, along with examples:

>     Greater than              5 > 4 is TRUE
<     Less than                 4 < 5 is TRUE
>=    greater than or equal     4 >= 4 is TRUE
<=    less than or equal        3 <= 4 is TRUE
==    Equal to                  5 == 5 is TRUE
!=    not equal to              5 != 4 is TRUE

It is highly probable that you have seen these before, probably with slightly different symbols. They should not present any hindrance to understanding. Now that you understand TRUE and FALSE in computer terminology as well as the comparison operators, let us look at the actual structure of if statements. 
Basic If Statement Syntax
The structure of an if statement is as follows:

if ( TRUE )
  Execute the next statement
Here is a simple example that shows the syntax: 
if ( 5 < 10 )
  cout<<"Five is now less than ten, that's a big surprise";

     Here, we're just evaluating the statement, "is five less than ten", to see if it is true or not; with any luck, it is! If you want, you can write your own full program including iostream and put this in the main function and run it to test. To have more than one statement execute after an if statement that evaluates to true, use braces, like we did with the body of a function. Anything inside braces is called a compound statement, or a block. 
For example:

if ( TRUE ) {
  Execute all statements inside the braces
I recommend always putting braces following if statements. If you do this, you never have to remember to put them in when you want more than one statement to be executed, and you make the body of the if statement more visually clear. 
Sometimes when the condition in an if statement evaluates to false, it would be nice to execute some code instead of the code executed when the statement evaluates to true. The "else" statement effectively says that whatever code after it (whether a single line or code between brackets) is executed if the if statement is FALSE. 
It can look like this:

if ( TRUE ) {
  // execute these statements if TRUE
else {
  // execute these statements if FALSE
Else If

Another use of else is when there are multiple conditional statements that may all evaluate to true, yet you want only one if statement's body to execute. You can use an "else if" statement following an if statement and its body; that way, if the first statement is true, the "else if" will be ignored, but if the if statement is false, it will then check the condition for the else if statement. If the if statement was true the else statement will not be checked. It is possible to use numerous else if statements to ensure that only one block of code is executed.

if ( <condition> ) {
  // Execute these statements if <condition> is TRUE
Else if ( <another condition> ) {
  // execute these statements if <another condition> is TRUE and
  // <condition> is FALSE

Let's look at a simple program for you to try out on your own. 

#include <iostream>
using namespace std;
int main()        // Most important part of the program!
  int age;         // Need a variable...
    cout<<"Please input your age: ";  // Asks for age
  cin>> age;      // The input is put in age
  cin.ignore();              // Throw away enter
  if ( age < 100 ) 
{                  // If the age is less than 100
         cout<<"You are pretty young!\n"; // Just to show you it works...
  else if ( age == 100 )
 {            // I use else just to show an example 
     cout<<"You are old\n";           // Just to show you it works...
    cout<<"You are really old\n";     // Executed if no other statement is

    More interesting conditions using Boolean operator’s Boolean operators allow you to create more complex conditional statements. For example, if you wish to check if a variable is both greater than five and less than ten, you could use the Boolean AND to ensure both var > 5 and var < 10 are true. In the following discussion of Boolean operators, I will capitalize the Boolean operators in order to distinguish them from normal English.

The actual C++ operators of equivalent function will be described further into the tutorial - the C++ symbols are not: OR, AND, NOT, although they are of equivalent function. 
When using if statements, you will often wish to check multiple different conditions. You must understand the Boolean operators OR, NOT, and AND. The Boolean operators function in a similar way to the comparison operators: each return 0 if evaluates to FALSE or 1 if it evaluates to TRUE.

NOT: The NOT operator accepts one input. If that input is TRUE, it returns FALSE, and if that input is FALSE, it returns TRUE. For example, NOT (1) evaluates to 0, 
And NOT (0) evaluates to 1. NOT (any number but zero) evaluates to 0. In C and C++ NOT is written as !. NOT is evaluated prior to both AND and OR.

AND: This is another important command. AND returns TRUE if both inputs are TRUE (if 'this' AND 'that' are true). (1) AND (0) would evaluate to zero because one of the inputs is false (both must be TRUE for it to evaluate to TRUE).(1) AND (1) evaluates to 1. (any number but 0) AND (0) evaluates to 0. The AND operator is written && in C++. Do not be confused by thinking it checks equality between numbers: it does not. Keep in mind that the AND operator is evaluated before the OR operator.

OR: Very useful is the OR statement! If either (or both) of the two values it checks are TRUE then it returns TRUE. For example, (1) OR (0) evaluates to 1. (0) OR (0) evaluates to 0. The OR is written as || in C++. Those are the pipe characters. On your keyboard, they may look like a stretched colon.
On my computer the pipe shares its key with \. Keep in mind that OR will be evaluated after AND. 
It is possible to combine several Boolean operators in a single statement; often you will find doing so to be of great value when creating complex expressions for if statements. What is!(1 && 0)? Of course, it would be TRUE. It is true is because 1 && 0 evaluates to 0 and!0 evaluates to TRUE (i.e., 1). 
Try some of these - they're not too hard. If you have questions about them, feel free to stop by my forums

A. !( 1 || 0 )         ANSWER: 0
B. !( 1 || 1 && 0 )    ANSWER: 0 (AND is evaluated before OR)
C. !( ( 1 || 0 ) && 0 )  ANSWER: 1 (Parenthesis are useful)

If you find you enjoyed this section, then you might want to look more at Boolean Algebra.


            Now that you should have learned about variables, loops, and conditional statements it is time to learn about functions. You should have an idea of their uses as we have already used them and defined one in the guise of main. cin.get() is an example of a function.
 In general, functions are blocks of code that perform a number of pre-defined commands to accomplish something productive. Functions that a programmer writes will generally require a prototype. Just like a blueprint, the prototype tells the compiler what the function will return, what the function will be called, as well as what arguments the function can be passed. When I say that the function returns a value, I mean that the function can be used in the same manner as a variable would be. 
   For example, a variable can be set equal to a function that returns a value between zero and four. 
For example:

#include <cstdlib>   // Include rand()
using namespace std; // Make rand() visible
int a = rand(); // rand is a standard function that all compilers have
 Do not think that 'a' will change at random , it will be set to the value returned 
when the function is called, but it will not change again. 
The general format for a prototype is simple: 

return-type function_name ( arg_type arg1, ..., arg_type argN );

arg_type just means the type for each argument -- for instance, an int, a float, or a char. It's exactly the same thing as what you would put if you were declaring a variable.
There can be more than one argument passed to a function or none at all (where the parentheses are empty), and it does not have to return a value. Functions that do not return values have a return type of void. Let's look at a function prototype:

int mult ( int x, int y );

This prototype specifies that the function mult will accept two arguments, both integers, and that it will return an integer. Do not forget the trailing semi-colon. Without it, the compiler will probably think that you are trying to write the actual definition of the function. 

When the programmer actually defines the function, it will begin with the prototype, minus the semi-colon. Then there should always be a block with the code that the function is to execute, just as you would write it for the main function. Any of the arguments passed to the function can be used as if they were declared in the block. Finally, end it all with a cherry and a closing brace. Okay, maybe not a cherry. 
Let's look at an example program:

#include <iostream>
using namespace std;
int mult ( int x, int y );
int main()
  int x;
  int y;
   cout<<"Please input two numbers to be multiplied: ";
  cin>> x >> y;
  cout<<"The product of your two numbers is "<< mult ( x, y ) <<"\n";
int mult ( int x, int y )
return x * y;

     This program begins with the only necessary include file and a directive to make the std namespace visible. Everything in the standard headers is inside of the std namespace and not visible to our programs unless we make them so. Next is the prototype of the function. Notice that it has the final semi-colon! The main function returns an integer, which you should always have to conform to the standard. You should not have trouble understanding the input and output functions.
 It is fine to use cin to input to variables as the program does. But when typing in the numbers, be sure to separate them by a space so that cin can tell them apart and put them in the right variables. 

Notice how cout actually outputs what appears to be the mult function. What is really happening is cout is printing the value returned by mult, not mult itself. The result would be the same as if we had use this print instead

cout<<"The product of your two numbers is "<< x * y <<"\n";

The mult function is actually defined below main. Due to its prototype being above main, the compiler still recognizes it as being defined, and so the compiler will not give an error about mult being undefined. As long as the prototype is present, a function can be used even if there is no definition.
 However, the code cannot be run without a definition even though it will compile. The prototype and definition can be combined into one also. If mult were defined before it is used, we could do away with the prototype because the definition can act as a prototype as well. 

Return is the keyword used to force the function to return a value. Note that it is possible to have a function that returns no value. If a function returns void , the return statement is valid, but only if it does not have an expression. In other words, for a function that returns void, the statement "return;" is legal, but redundant. 
The most important functional (Pun semi-intended) question is why do we need a function? Functions have many uses. 
For example, a programmer may have a block of code that he has repeated forty times throughout the program. A function to execute that code would save a great deal of space, and it would also make the program more readable. Also, having only one copy of the code makes it easier to make changes. Would you rather make forty little changes scattered all throughout a potentially large program, or one change to the function body? So would I. 

Another reason for a function is to break down a complex program into logical parts. For example, take a menu program that runs complex code when a menu choice is selected. The program would probably best be served by making functions for each of the actual menu choices, and then breaking down the complex tasks into smaller, more manageable tasks, which could be in their own functions. In this way, a program can be designed that makes sense when read. And has a structure that is easier to understand quickly. The worst programs usually only have the required function, main, and fill it with pages of jumbled code.