"Go foundation" Section 7 variables

1. What is a variable?

We should be how to understand the variables here I want to give an example?:

We should all know the glory of the king of this game. When we play king of glory, we control the hero's blood is constantly changing, the blood is the presence of memory. So this blood is a variable .

The program is running, the amount of the value can be changed, we called variables.

The above can be found by way of example:

• Variables are stored in memory
• Variables can be changed

We say that the variable is stored in memory, so memory, what is it?

Memory is a continuous collection of data in each memory storage area has a unique address identifier, called a memory address. We like the same ID, each person has a unique ID.

We know what the variables are, then the Go language, variables should be how to define it?

2. Variable

2.1 Definition of variables

Go basic variable definition is to use varthe keyword, the basic format is:

var 变量名 数据类型

Declare variables with keyword varat the beginning, end of line does not require a semicolon

For example, we define a name hp, the type intof variables:

var hp int  // int表示为整型

Let's declare a variable and print it and see:

package main

import "fmt"

func main() {
    // 使用 var 定义一个变量, 注意: 变量类型要放在变量名后面
    var hp int
    fmt.Println(hp)
}

// 结果:
0

Strange? I did not give a specific value hp, how to print out 0 it?

In fact, this is a feature Go: When we declare a default value for a variable time, if no initial value, Go give it a corresponding type.

In this case, we gave hpa value of it.

package main

import "fmt"

func main() {
    // 使用 var 定义一个变量, 注意: 变量类型要放在变量名后面
    var hp int
    hp = 100  // 赋值操作
    fmt.Println(hp)
}

// 结果:
100

Of course, we can also directly when it was declared hpa value:

var hp int = 100  // 定义变量并初始化值

If we simply define a variable and not to use it, then the Go will error.

2.2 define multiple variables

// 定义两个个类型都是int的变量
var hp, mp int

Since you can define multiple variables at the same time, it also can initialize multiple variables simultaneously

/*定义两个类型都是"int"的变量, 并且分别初始化为相应的值
hp为100, mp为260
*/
var hp, mp int = 100, 260

2.3 Automatic Derivation types

Have not found some complicated when we define a variable, you need to write 类型, Go not allow us to write 类型, it will automatically help us derive the corresponding data type:

var hp, mp = 100, 260

Some people say, that varcan also go, every time writing, good trouble no problem, Go also allows you to:

/*定义两个变量，它们分别初始化为相应的值
hp为100, mp为260
编译器会根据初始化的值自动推导出相应的类型
*/
hp, mp := 100, 260  // 注意这里有个冒号 :

Now I am not feeling very concise. :=This symbol is a direct replacement for the definition and assignment variables.

hp := 100
// 等价于下面两行
var hp int
hp = 100

But it has a limitation that can be used only within the function; the function will not use external compiler, it is generally a varway to define global variables.

2.4 anonymous variable

_(Underscore) as the anonymous variable , it will discard the corresponding data is not processed. Anonymous variables with the function's return value to use value only, now we can to know their grammar.

In the following example, we have the value 2given bdiscarded3

_, b := 3, 2

Anonymous variable name do not take up space, it does not allocate memory.

Not because of repeated statements can not be used between variables and anonymous anonymous variable.

2.5 Variable naming convention

1. Variables can only consist of letters, numbers, underscores.
2. You can not start with a number.
3. Go is not the keywords and reserved words
4. Case sensitivity, a := 1and A := 1the two variables.

The above requirements must be met, the following requirements to try to make

1. Descriptive variable names have to be concise, easy to read, not too long.
2. Variable names can not use Chinese and pinyin.
3. Recommended variable names:
   • Underline: my_name = 'Conan'
   • Hump ​​body: MyName = 'Conan'

Go language 25 Keywords:

break        default      func         interface    select
case         defer        go           map          struct
chan         else         goto         package      switch
const        fallthrough  if           range        type
continue     for          import       return       var

Go language 37 reserved words:

Constants:    true  false  iota  nil
    Types:    int  int8  int16  int32  int64
              uint  uint8  uint16  uint32  uint64  uintptr
              float32  float64  complex128  complex64
              bool  byte  rune  string  error
Functions:    make  len  cap  new  append  copy  close  delete
              complex  real  imag
              panic  recover