C++ Language

C++ Programming:-

C++ is an object oriented programming (OOP) language, developed by Bjarne Stroustrup, and is an extension of C language. It is therefore possible to code C++ in a "C style" or "object-oriented style."

The C++ programming language has a history going back to 1979, when Bjarne Stroustrup was doing work for his Ph.D. thesis. One of the languages Stroustrup had the opportunity to work with was a language called Simula, which as the name implies is a language primarily designed for simulations. C++ is widely used in industry for commercial software development. It is an industrial strength programming language used for developing complex systems in business, science, and engineering. Examples of software written in C++ include Microsoft Windows 8, Microsoft Office, Mac OS X, and Adobe Creative Suite.

Compiler Translate high-level language to machine language. Check that the program obeys the rules. The original program in a high level language is called source code. The translated version in machine language is called objective code.  

 Some programs we use are already compiled. Their object code is available for us to use. For example:  Input and output Routines.

A Linker combines the object code for the programs we write, the object code for the pre-compiled routines (of SDK), the machine language program the CPU can run.Loader loads executable program into main memory. The last step is to execute the program.

C++ is a free-format language, which means that:

Extra blanks (spaces) or tabs before or after identifiers/operators are ignored. 

Blank lines are ignored by the compiler just like comments.

Code can be indented in any way.

There can be more than one statement on a single line.

A single statement can continue over several lines.

A debugger allows a programmer to more easily trace a program’s execution in order to locate and correct errors in the program’s implementation. With a debugger, a developer can simultaneously run a program and see which line in the source code is responsible for the program’s current actions. The programmer can watch the values of variables and other program elements to see if their values change as expected. Debuggers are valuable for locating errors (also called bugs) and repairing programs that contain errors.

We now introduce C++ programming, which facilitates a disciplined approach to program design. Most of the C++ programs you’ll study in this book process information and display results. In this chapter, we present five examples that demonstrate how your programs can display messages and obtain information from the user for processing. The first three examples simply display messages on the screen. The next obtains two numbers from a user, calculates their sum and displays the result. The accompanying discussion shows you how to perform arithmetic calculations and save their results for later use. The fifth example demonstrates decision-making by showing you how to compare two numbers, then display messages based on the comparison results. We analyze each program one line at a time to help you ease your way into C++ programming.

// Text-printing program.

#include <iostream> // allows program to output data to the screen

using namespace std;

int main()// function main begins program execution

{

       cout<< "Welcome to C++!\n"; // display message

       system("pause");// indicate that program ended successfully

       return 0;

}// end function main

// Text-printing program.

// allows program to output data to the screen

Each begin with //, indicating that the remainder of each line is a comment. You insert comments to document your programs and to help other people read and understand them. Comments do not cause the computer to perform any action when the program is run—they’re ignored by the C++ compiler and do not cause any machine-language object code to be generated. The comment Text-printing program describes the purpose of the program. A comment beginning with // is called a single-line comment because it terminates at the end of the current line. [Note: You also may use C’s style in which a comment— possibly containing many lines—begins with /* and ends with */.]

#include <iostream

is a preprocessor directive, which is a message to the C++ preprocessor. Lines that begin with # are processed by the preprocessor before the program is compiled. This line notifies the preprocessor to include in the program the contents of the input/output stream header <iostream>. This header must be included for any program that outputs data to the screen or inputs data from the keyboard using C++’s stream input/output.

Blank Lines and White Space

Line 4 is simply a blank line. You use blank lines, space characters and tab characters (i.e., “tabs”) to make programs easier to read. Together, these characters are known as white space. White-space characters are normally ignored by the compiler.

The main Function

Line 5

// function main begins program execution

Is another single-line comment indicating that program execution begins at the next line.

Line 6

int main()

is a part of every C++ program. The parentheses after main indicate that main is a program building block called a function. C++ programs typically consist of one or more functions and classes (as you’ll learn in Chapter 3). Exactly one function in every program must be named main. Figure 2.1 contains only one function. C++ programs begin executing at function main, even if main is not the first function in the program. The keyword int to the left of main indicates that main “returns” an integer (whole number) value. A keyword is a word in code that is reserved by C++ for a specific use. The complete list of C++ keywords can be found in Fig. 4.3. We’ll explain what it means for a function to “return a value” when we demonstrate how to create your own functions in Section 3.3. For now,

simply include the keyword int to the left of main in each of your programs. The left brace, {, (line 7) must begin the body of every function. A corresponding right brace, }, (line 11) must end each function’s body.

An Output Statement

Line 8

cout<< "Welcome to C++!\n";

instructs the computer to perform an action—namely, to print the string of characters contained between the double quotation marks. A string is sometimes called a character string or a string literal. We refer to characters between double quotation marks simply as strings. White-space characters in strings are not ignored by the compiler. The entire line 8, including cout, the << operator, the string "Welcome to C++!\n" and the semicolon (;), is called a statement. Every C++ statement must end with a semicolon (also known as the statement terminator). Preprocessor directives (like #include) do not end with a semicolon. Output and input in C++ are accomplished with streams of characters. Thus, when the preceding statement is executed, it sends the stream of characters Welcome to C++!\n to the standard output stream object-cout-which is normally “connected” to the screen.

The Stream Insertion Operator and Es’cape Sequences

The << operator is referred to as the stream insertion operator. When this program executes, the value to the operator’s right, the right operand, is inserted in the output stream. Notice that the operator points in the direction of where the data goes. The right operand’s characters normally print exactly as they appear between the double quotes. However, the characters \n are not printed on the screen (Fig. 2.1). The backslash (\) is called an escape character. It indicates that a “special” character is to be output. When a backslash is encountered in a string of characters, the next character is combined with the backslash to form an escape sequence. The escape sequence \n means newline. It causes the cursor (i.e., the current screen-position indicator) to move to the beginning of the next line on the screen.