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【2.C#基础】4.变量

作者：青少年编程ABC

4.变量

4.1变量类型

在 C# 中，变量类型如下表所示：

数据 类型 描述 示例 说明
整型 byte 0 ~ 255 byte num=1;
short -32768 ~ 32768 short num=300;
int -2147483648 ~ 2147483647 int age=18; 大部分情况下整数类型使用int
long -2^63 ~ 2^63-1 long num=10;
单精度浮点型 float -3.4x10^38 ~ +3.4x10^38 float f=0.0f;
双精度浮点型 double (+/-)5.0x10^-324 ~ (+/-)1.7x10^308 double d=0.0d;
字符型 char 单个字符 （字母数字符号汉字等） char c='a'; 字符的值使用单引号
布尔型 bool 值为真或假 bool b = true; true为真，false为假
字符串型 string 多个字符 string name="张三"; 字符串的值使用双引号

4.2变量声明

变量声明的方法：

类型名 变量名;

如：

int i, j, k;
char c, ch;
float f, salary;
double d;

变量初始化：

变量名 = 值;
类型名 变量名 = 值;

如：

int d = 3, f = 5;    /* 初始化 d 和 f. */
byte z = 22;         /* 初始化 z. */
double pi = 3.14159; /* 声明 pi 的近似值 */
char x = 'x';        /* 变量 x 的值为 'x' */

变量初始化时的"="称为赋值符，赋值就是将值放入变量中。

变量的赋值：

变量名 = 值;
变量名 = 变量名;

示例：

整数示例

using System.Collections;
using System.Collections.Generic;
using UnityEngine;

public class DemoInt : MonoBehaviour
{
    // Start is called before the first frame update
    void Start()
    {
        int a = 1;
        Debug.Log(a);
        int b = 2;
        Debug.Log(b);
        b = a;
        Debug.Log(b);
    }

    // Update is called once per frame
    void Update()
    {
        
    }
}

控制台输出：

1
UnityEngine.Debug:Log(Object)
DemoInt:Start() (at Assets/DemoInt.cs:11)
2
UnityEngine.Debug:Log(Object)
DemoInt:Start() (at Assets/DemoInt.cs:13)
1
UnityEngine.Debug:Log(Object)
DemoInt:Start() (at Assets/DemoInt.cs:15)

浮点数示例

using System.Collections;
using System.Collections.Generic;
using UnityEngine;

public class DemoDecimal : MonoBehaviour
{
    // Start is called before the first frame update
    void Start()
    {
        float f = 0.0f;
        Debug.Log(f);
        float x = 1.0f;
        Debug.Log(x);
        f = x;
        Debug.Log(f);
    }

    // Update is called once per frame
    void Update()
    {
        
    }
}

控制台输出：

0
UnityEngine.Debug:Log(Object)
DemoDecimal:Start() (at Assets/DemoDecimal.cs:11)
1
UnityEngine.Debug:Log(Object)
DemoDecimal:Start() (at Assets/DemoDecimal.cs:13)
1
UnityEngine.Debug:Log(Object)
DemoDecimal:Start() (at Assets/DemoDecimal.cs:15)

字符串示例

using System.Collections;
using System.Collections.Generic;
using UnityEngine;

public class DemoString : MonoBehaviour
{
    // Start is called before the first frame update
    void Start()
    {
        string s = "I am a student.";
        Debug.Log(s);
    }

    // Update is called once per frame
    void Update()
    {
        
    }
}

控制台输出：

I am a student.
UnityEngine.Debug:Log(Object)
DemoString:Start() (at Assets/DemoString.cs:11)

4.3变量运算

  • 加法 +
  • 减法 -
  • 乘法 *
  • 除法 /

变量之间也可以进行运算。

示例：

using System.Collections;
using System.Collections.Generic;
using UnityEngine;

public class Operation : MonoBehaviour
{
    // Start is called before the first frame update
    void Start()
    {
        int a = 1, b = 2;
        int c = a + b;
        Debug.Log(c);  // 3
        Debug.Log(a - c);  // -2
        Debug.Log(b * c);  // 6
        Debug.Log(c * 1.0 / b);  // 1.5
    }

    // Update is called once per frame
    void Update()
    {
        
    }
}

控制台输出：

3
UnityEngine.Debug:Log(Object)
Operation:Start() (at Assets/Operation.cs:12)
-2
UnityEngine.Debug:Log(Object)
Operation:Start() (at Assets/Operation.cs:13)
6
UnityEngine.Debug:Log(Object)
Operation:Start() (at Assets/Operation.cs:14)
1.5
UnityEngine.Debug:Log(Object)
Operation:Start() (at Assets/Operation.cs:15)

在上面的代码中，为什么要 c * 1.0 / b 而不是 c / b 呢？因为在 C# 中两个整型数相除得到的仍然是整型数，也就是说 c / b 的结果是1，而不是 1.5，c * 1.0 / b 是将运算中的分母转换为浮点型数，得到的结果就是 1.5。

  • +=、-=、*=、/=

如果给一个变量加上或减去一个数值，表达式可以写成：a = a + 5 或者 a = a - 5。这条语句比较好理解：先用 a 的值加上或减去 5，然后赋值给变量 a。在 C# 中，提供了更加简洁的运算符 +=、-=、*=、/=，通过如下写法即可实现上面的操作。

变量 += 值|变量;
变量 -= 值|变量;
变量 *= 值|变量;
变量 /= 值|变量;

示例：

using System.Collections;
using System.Collections.Generic;
using UnityEngine;

public class Operation : MonoBehaviour
{
    // Start is called before the first frame update
    void Start()
    {
        int a = 8, b = 2;
        a += b;
        Debug.Log(a);  // 10
        a *= b;
        Debug.Log(a);  // 20
        a -= b;
        Debug.Log(a);  // 18
        a /= b;
        Debug.Log(a);  // 9
    }

    // Update is called once per frame
    void Update()
    {
        
    }
}

控制台输出：

10
UnityEngine.Debug:Log(Object)
Operation:Start() (at Assets/Operation.cs:12)
20
UnityEngine.Debug:Log(Object)
Operation:Start() (at Assets/Operation.cs:14)
18
UnityEngine.Debug:Log(Object)
Operation:Start() (at Assets/Operation.cs:16)
9
UnityEngine.Debug:Log(Object)
Operation:Start() (at Assets/Operation.cs:18)
  • ++、--

在 C# 中，将变量值加1或减1，可以使用 ++ 或 --，称为自增运算符或自减运算符。格式：

变量++;
变量--;
++变量;
--变量;

变量出现在运算符前后表示 “先使用变量再执行操作” 或者 “先执行操作再使用变量值”。

示例：

using System.Collections;
using System.Collections.Generic;
using UnityEngine;

public class Operation : MonoBehaviour
{
    // Start is called before the first frame update
    void Start()
    {
        int a = 8, b = 2;
        Debug.Log(a++);  // 输出8，a的值变化为9
        Debug.Log(a);    // 输出9
        Debug.Log(++b);  // b的值变化为3，输出3
        Debug.Log(a--);  // 输出9，a的值变化为8
        Debug.Log(a);    // 输出8
        Debug.Log(--b);  // b的值变化为2，输出2
    }

    // Update is called once per frame
    void Update()
    {
        
    }
}

控制台输出：

8
UnityEngine.Debug:Log(Object)
Operation:Start() (at Assets/Operation.cs:11)
9
UnityEngine.Debug:Log(Object)
Operation:Start() (at Assets/Operation.cs:12)
3
UnityEngine.Debug:Log(Object)
Operation:Start() (at Assets/Operation.cs:13)
9
UnityEngine.Debug:Log(Object)
Operation:Start() (at Assets/Operation.cs:14)
8
UnityEngine.Debug:Log(Object)
Operation:Start() (at Assets/Operation.cs:15)
2
UnityEngine.Debug:Log(Object)
Operation:Start() (at Assets/Operation.cs:16)
  • 字符串连接

字符串也可以使用 + 和 += 运算符，其结果为将字符串连接起来，如："abc" + “def" 的结果为："abcdef"。

示例：

using System.Collections;
using System.Collections.Generic;
using UnityEngine;

public class Operation : MonoBehaviour
{
    // Start is called before the first frame update
    void Start()
    {
        string a = "Happy ", b = "new year!";
        Debug.Log(a + b);
        a += b;
        Debug.Log(a);
    }

    // Update is called once per frame
    void Update()
    {
        
    }
}

控制台输出：

Happy new year!
UnityEngine.Debug:Log(Object)
Operation:Start() (at Assets/Operation.cs:11)
Happy new year!
UnityEngine.Debug:Log(Object)
Operation:Start() (at Assets/Operation.cs:13)
  • 字符串与数值连接

+ 和 += 运算符也可以用于字符串与数值的链接，此时，数值被当作字符串来处理。

示例：

using System.Collections;
using System.Collections.Generic;
using UnityEngine;

public class Operation : MonoBehaviour
{
    // Start is called before the first frame update
    void Start()
    {
        string a = "Happy ";
        int b = 123;
        float c = 0.05f;
        Debug.Log(a + b);
        Debug.Log(a + c);
        Debug.Log(a + b + c);
    }

    // Update is called once per frame
    void Update()
    {
        
    }
}

控制台输出：

Happy 123
UnityEngine.Debug:Log(Object)
Operation:Start() (at Assets/Operation.cs:13)
Happy 0.05
UnityEngine.Debug:Log(Object)
Operation:Start() (at Assets/Operation.cs:14)
Happy 1230.05
UnityEngine.Debug:Log(Object)
Operation:Start() (at Assets/Operation.cs:15)
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