Chapter 2 - Structure of C++ Program
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This document provides an overview of the components of a simple "Hello World" C++ program, including comments, header files, namespaces, functions, output statements, and escape sequences. It explains that main is the first function executed, iostream is included for input/output, namespace std contains standard library elements, cout with << prints output, and return 0 indicates successful completion. It also demonstrates using escape sequences like \n to print multiple lines with a single statement.
Chapter 2 - Structure of C++ Program
- 1. www.cppforschool.com First program is C++ // This is my first program is C++ /* this program will illustrate different components of a simple program in C++ */ #include <iostream> using namespace std; int main() { cout << "Hello World!"; return 0; } When the above program is compiled, linked and executed, the following output is displayed on the VDU screen. Hello World! Various components of this program are discussed below: Comments First three lines of the above program are comments and are ignored by the compiler. Comments are included in a program to make it more readable. If a comment is short and can be accommodated in a single line, then it is started with double slash sequence in the first line of the program. However, if there are multiple lines in a comment, it is enclosed between the two symbols /* and */ #include <iostream> The line in the above program that start with # symbol are called directives and are instructions to the compiler. The word include with '#' tells the compiler to include the file iostream into the file of the above program. File iostream is a header file needed for input/ output requirements of the program. Therefore, this file has been included at the top of the program.
- 2. using namespace std; All the elements of the standard C++ library are declared within std. This line is very frequent in C++ programs that use the standard library. int main ( ) The word main is a function name. The brackets ( ) with main tells that main ( ) is a function. The word int before main ( ) indicates that integer value is being returned by the function main (). When program is loaded in the memory, the control is handed over to function main ( ) and it is the first function to be executed. Curly bracket and body of the function main ( ) A C++ program starts with function called main(). The body of the function is enclosed between curly braces. The program statements are written within the brackets. Each statement must end by a semicolon, without which an error message in generated. cout<<"Hello World!"; This statement prints our "Hello World!" message on the screen. cout understands that anything sent to it via the << operator should be printed on the screen. return 0; This is a new type of statement, called a return statement. When a program finishes running, it sends a value to the operating system. This particular return statement returns the value of 0 to the operating system, which means “everything went okay!”. Printing Multiple Lines of Text with a Single Statement /* This program illustrates how to print multiple lines of text with a single statement */ #include <iostream> using namespace std; int main() {
- 3. cout << "WelcomentonC++"; return 0; } Output: Welcome to C++ The characters print exactly as they appear between the double quotes. However, if we type n, the characters n are not printed on the screen. 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 to move to the beginning of the next line on the screen. The following table gives a listing of common escape sequences. Escape Sequence Description n Newline t Horizontal tab a Bell (beep) Backslash ' Single quote '' Double quote