C++ basic syntax

C++ Program Structure

Let us look at a simple code that can output the word Hello World.

#include <iostream>
using namespace std;

// main() 是程序开始执行的地方

int main()
{
   cout << "Hello World"; // 输出 Hello World
   return 0;
}

Next let’s explain the above program:

• The C++ language defines some header files, which contain necessary or useful information in the program. . The above program includes the header file <iostream>.

• Line using namespace std; tells the compiler to use the std namespace. Namespaces are a relatively new concept in C++.

• Next line // main() is where the program starts execution is a single line comment. Single-line comments begin with // and end at the end of the line.

• Next line int main() is the main function, and the program execution starts from here.

• Next line cout << "Hello World"; will display the message "Hello World" on the screen.

• Next line return 0; Terminate the main() function and return the value 0 to the calling process.

Compiling & Executing C++ Programs

Next let’s see how to save the source code in a file, and how to compile and run it. Here are the simple steps:

• Open a text editor and add the above code.

• Save the file as hello.cpp.

• Open the command prompt and enter the directory where the file is saved.

• Type 'g++ hello.cpp' and press Enter to compile the code. If there are no errors in the code, the command prompt jumps to the next line and generates the a.out executable file.

• Now, type ' a.out' to run the program.

• You can see 'Hello World' displayed on the screen.

$ g++ hello.cpp
$ ./a.out
Hello World

Make sure you have the g++ compiler in your path, and make sure you are running it in the directory containing the source file hello.cpp.

You can also use makefile to compile C/C++ programs.

Semicolon & Block in C++

In C++, the semicolon is the statement terminator. That is, each statement must end with a semicolon. It indicates the end of a logical entity.

For example, here are three different statements:

x = y;
y = y+1;
add(x, y);

A block is a group of logically connected statements enclosed in curly braces. For example:

{
   cout << "Hello World"; // 输出 Hello World
   return 0;
}

C++ does not end with end-of-line identifiers, so you can put multiple statements on one line. For example:

x = y;
y = y+1;
add(x, y);

is equivalent to

x = y; y = y+1; add(x, y);

C++ identifier

C++ identifier is used to identify variables, functions, classes, modules, or any other user-defined items name. An identifier begins with the letters A-Z or a-z or the underscore _, followed by zero or more letters, underscores, and numbers (0-9).

Punctuation characters such as @, $, and % are not allowed within C++ identifiers. C++ is a case-sensitive programming language. Therefore, in C++, Manpower and manpower are two different identifiers.

Several valid identifiers are listed below:

mohd       zara    abc   move_name  a_123
myname50   _temp   j     a23b9      retVal

C++ Keywords

The following table lists the reserved words in C++. These reserved words cannot be used as constant names, variable names, or other identifier names.

##auto enumoperatorthrow##boolbreakcase##catchfalseregister typeidcharfloatreinterpret_casttypenameclassforreturnunionfriendgotoifinlineintlongmutablenamespaceTrigram

asm	else	new	this
explicit	private	true
export	protected	try
extern	public	typedef
			##const
short	unsigned		const_cast
signed	using		continue
sizeof	virtual		default
static	void		delete
static_cast	volatile		do
struct	wchar_t		double
switch	while		dynamic_cast
template

Trigram is a sequence of three characters used to represent another character, also known as a three-character sequence. Three-character sequences always begin with two question marks.

Three-character sequences are less common, but the C++ standard allows certain characters to be specified as three-character sequences. In the past, this was an essential method to represent characters that were not available on the keyboard.

Three-character sequences can appear anywhere, including strings, character sequences, comments, and preprocessing directives.

The most commonly used three-character sequences are listed below:

three-character groupreplace\^##??([??)]

	??=
	??/
	?? '
##??!	|
??<	{
??>	}
??-	~
All compilers do not support three-character groups. To avoid confusion, it is not recommended to use three-character groups. Spaces in C++ Lines that contain only spaces are called blank lines and may be commented, and the C++ compiler will ignore them completely. In C++, spaces are used to describe whitespace, tabs, newlines, and comments. Whitespace separates parts of a statement, allowing the compiler to identify where one element in the statement (such as an int) ends and the next element begins. So, in the following statement: int age; Here, there must be at least one space character (usually a whitespace character) between int and age so that the compiler can distinguish them. On the other hand, in the following statement: fruit = apples + oranges;   // 获取水果的总数 The space character between fruit and =, or = and apples is not required, but you can add some spaces if needed to enhance readability. ← C++ environment settings C++ comments → submit php.cn HomeCourseArticleQ&ADictionaryManualDownloadsearch APPDownload