C# constants

Integer constants

Integer constants can be decimal, octal or hexadecimal constants. The prefix specifies the base: 0x or 0X for hexadecimal, 0 for octal, and no prefix for decimal.

Integer constants can also have suffixes, which can be a combination of U and L, where U and L represent unsigned and long respectively. Suffixes can be uppercase or lowercase, and multiple suffixes can be combined in any order.

Here are some examples of integer constants:

212         /* 合法 */
215u        /* 合法 */
0xFeeL      /* 合法 */
078         /* 非法：8 不是一个八进制数字 */
032UU       /* 非法：不能重复后缀 */

The following are examples of various types of integer constants:

85         /* 十进制 */
0213       /* 八进制 */
0x4b       /* 十六进制 */
30         /* int */
30u        /* 无符号 int */
30l        /* long */
30ul       /* 无符号 long */

Floating point constants

A float Point constants are composed of integer part, decimal point, decimal part and exponent part. You can represent floating-point constants in decimal or exponential form.

Here are some examples of floating point constants:

3.14159       /* 合法 */
314159E-5L    /* 合法 */
510E          /* 非法：不完全指数 */
210f          /* 非法：没有小数或指数 */
.e55          /* 非法：缺少整数或小数 */

When expressed in decimal form, it must contain the decimal point, the exponent, or both. When expressed in exponential form, it must contain an integer part, a decimal part, or both. Signed exponents are represented by e or E.

Character constants

Character constants are enclosed in single quotes, for example, 'x', and can be stored in a simple character type variable. A character constant can be an ordinary character (such as 'x'), an escape sequence (such as '\t'), or a universal character (such as '\u02C0').

There are some specific characters in C# that have special meaning when preceded by a backslash and can be used to represent a newline character (\n) or a tab character (\t). Here, list some escape sequence codes:

##\?? Characters\aAlert or bell\bBackspace\fForm feed\nLine break (Newline)\rEnter\tHorizontal tab tab\vVertical tab tab\oooOne to three octal numbers\xhh . . .One or more digits Hexadecimal number

The following are some examples of escape sequence characters:

namespace EscapeChar
{
    class Program
    {
        static void Main(string[] args)
        {
            Console.WriteLine("Hello\tWorld\n\n");
            Console.ReadLine();
        }
    }
}

When the above code is compiled and executed, it produces the following results:

Hello   World

String constants

Character constants are enclosed in double quotes "", or enclosed in @"". The characters contained in string constants are similar to character constants, which can be: ordinary characters, escape sequences and universal characters

When using string constants, you can split a long line into multiple lines, you can use Spaces separate sections.

Here are some examples of string constants. The various forms listed below represent the same string.

"hello, dear"
"hello, \
dear"
"hello, " "d" "ear"
@"hello dear"

Define constants

Constants are defined using the const keyword. The syntax for defining a constant is as follows:

const <data_type> <constant_name> = value;

The following code demonstrates how to define and use constants in a program:

using System;

namespace DeclaringConstants
{
    class Program
    {
        static void Main(string[] args)
        {
            const double pi = 3.14159; // 常量声明
            double r;
            Console.WriteLine("Enter Radius: ");
            r = Convert.ToDouble(Console.ReadLine());
            double areaCircle = pi * r * r;
            Console.WriteLine("Radius: {0}, Area: {1}", r, areaCircle);
            Console.ReadLine();
        }
    }
}

When the above code is compiled and executed, it will produce the following results ：

Enter Radius: 
3
Radius: 3, Area: 28.27431

Escape sequence	Meaning
\\	\ characters
\'	' characters
\"	"Characters