[C++ Entry Guide] (04) Basic Grammar

1. Notes

Function : Add some instructions and explanations to the code, so that you or other programmers can read the code.

There are two kinds of annotations in C++:

1. Single-line comment : // description information

   • Usually placed above a line of code, or at the end of a statement, to explain the line of code.

2. Multi-line comment (delimiter pair comment) : /* description information */

   • Usually placed above a line of code, it describes the code as a whole.

Tip: When the compiler compiles the code, it will ignore the content of the comment

Example :

#include <iostream>

using namespace std;

/*
* 简单的主函数：
* 读取两个数，求它们的和
*/
int main( )
{
    
    
	// 提示用户输入两个数
	cout << "Please Enter two numbers:" << endl;

	int v1 = 0, v2 = 0;    // 保存我们读入的输入数据的变量

	cin >> v1 >> v2;      // 读取输入数据

	cout << "The sum of " << v1 << "and" << v2
		<< " is " << v1 + v2 << endl;

	return 0;
}

2. Variables

Function : Name a specified memory space to facilitate the operation of this memory

Syntax : data type variable name = initial value;

Example :int num = 100;

3. Constants

Function : used to record unchangeable data in the program

There are two ways to define constants in C++:

1. #define macro constants:#define 常量名 常量值
   • Usually defined above the file, representing a constant
2. Variables modified by const:const 数据类型 常量名 = 常量值
   • Usually, the keyword const is added before the variable definition to modify the variable as a constant and cannot be modified

Example :

#include <iostream>

using namespace std;

#define WEEK_DAY 7

int main()
{
    
    
	
	cout << "一周共有 " << WEEK_DAY << " 天"<< endl;

	const int month = 12;

	cout << "一年共有 " << month << " 个月" << endl;

	return 0;
}

4. Keywords

Role : keywords are pre-reserved words (identifiers) in C++

Tip: When defining variables or constants, do not use keywords

The C++ keywords are as follows:

5. Identifier

Role : The name used to identify variables, functions, classes, modules, or any other user-defined items.

Naming rules :

• Identifiers cannot be keywords;
• Identifiers can only consist of letters, numbers, and underscores
• The first character must be a letter or underscore
• Identifier Chinese letters are case sensitive

Suggestion: When naming an identifier, strive to achieve the effect of knowing the name and knowing it, so that it is convenient for yourself and others to read