[c# tutorial] C# constants

C# Constants

Constants are fixed values ​​that will not change during program execution. Constants can be of any basic data type, such as integer constants, floating point constants, character constants or string constants, as well as enumeration constants.

Constants can be treated as regular variables, but their values ​​cannot be modified after they are defined.

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 stand for 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 */

Here 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, you must include 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 they are preceded by a backslash and can be used to represent a newline (n) or a tab (t) character. Here, some escape sequence codes are listed:

Escape sequence

Meaning

\ Character

' ' ' character

" " character

? ? character

a Alert or bell

b Backspace

f Form feed

n Newline

r Carriage return

t Horizontal tab

v Vertical tab

ooo One to three digits in octal number

xhh . . . One or more digits in 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 brackets 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 produces the following results :

Enter Radius: 
3
Radius: 3, Area: 28.27431

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