One 、 Introduction of variables

• What is a variable ： Variables are used to describe the data storage space in the computer
• Role of variables ： Is to save data in computer memory
• Declaration of variables ：var Variable name type

package main

import "fmt"

func main()  {
    
	var age int
	var num, sum int
	fmt.Println(age)
	fmt.Println(num)
	fmt.Println(sum)
}

• Variable initialization ： You can assign values to variables when you define them , This process initializes variables

package main

import "fmt"

func main()  {
    
  var age int = 10
  var num int = 20
  fmt.Println(age, num)
}

• Variable assignment ： After the variable is defined , And assign values to variables , That is, declaration before assignment

func main()  {
    
	var a int = 10
	var b int
	b = a
	fmt.Println(b)
}

• Case study ： In exchange for 2 Values of variables

func main()  {
    
	var num1 int = 10
	var num2 int = 20
	var temp int
	temp = num1
	num1 = num2
	num2 = temp
	fmt.Println(num1, num2)
}

• Automatic derivation type ： The so-called automatic derivation type , Just don't go through var Declare variables , Don't specify type , Directly follow the variable name with ”:” Number , Complete the assignment at the same time . that GO The type of variable will be automatically deduced according to the assigned value . If num The variable is assigned a decimal number , Then the type of the variable is decimal （ floating-point ）

func main()  {
    
	num := 10
	num1 := 20
	a, b, c :=12, 13, 14
	fmt.Println(num, num1)
	fmt.Println(a, b, c)
}

• Case study ： In exchange for 2 Values of variables （ Realization 2）

func main()  {
    
	num1 := 10
	num2 := 20
	num1, num2 = num2,num1
	fmt.Println(num1,num2)

}

Two 、 Input and output format control

• Println： Formatted output
• Printf： Format output ,%d Indicates that the output is the value in an integer variable ,\n Means line break

func main()  {
    
	num1 := 10
	num2 := 20
	num3 := 30
	fmt.Println(num1, num2, num3)
	fmt.Println("num1=", num1)
	fmt.Printf("num1 = %d\n", num1)
	fmt.Printf("num2 = %d,num3 = %d",num2, num3)
}

• Scanf：Scanf() Grammar format ：fmt.Scanf(“%d”,&num)
• Scan：Scan() Grammar format ： fmt.Scan(&num)
• Variable address ： In memory, corresponding storage units will be opened up for variables , In order to be able to find the storage unit, access data , The system will add a number to each unit , This number is the address
• Scan and Scanf The difference between ：Scan You do not need to specify a formatter , later stage Scan More frequently used

package main

import "fmt"

func main()  {
    
	var age int
	fmt.Println(" Please enter age :")
	/* fmt.Scanf("%d",&age) //  adopt Scanf The function assigns the data entered by the keyboard to the variable , But variables must be preceded by & fmt.Println("age = ",age) fmt.Println(&age) fmt.Printf("%p",&age) */
	fmt.Scan(&age)
	fmt.Println("age = ", age)
}

3、 ... and 、 Computer base system

A simple understanding of , And there are a lot of information on the Internet , Including binary conversion and so on

• What is base ： The method of counting according to the principle of carry is called carry counting system .“ Carry numeration system ” Referred to as “ Number system ” or “ Base number ”
  • The carry of each number system follows a rule , That's it ---- Meet N Into the 1
• Hexadecimal features
  • Use a fixed set of numbers to represent the size of the value . Such as ： The decimal number is 0,1,2,3,4,5,6,7,8,9
  • Uniform rules ： Meet N Jin Yi
• Binary element
  • base ： there N It's called cardinality . So-called “ base ” It refers to the number of basic digits allowed in various binary counting systems
  • Position right ：215=2*10² + 1*10¹ + 5*10⁰ , among 10² , 10¹ ,10⁰ Position right
  • Add by weight ： Multiply the numeric character on each bit by the weight it represents

Four 、 Variable naming conventions

• Naming specification
  • ①. Only numbers , Letter ,_（ Underline ） form
  • ②. Cannot start with a number
  • ③. Capital letters and lowercase letters are different ：heapSort and Heapsort It's two different names
  • ④. It can't be a keyword
• Naming rules
  • Hump nomenclature
    • Little hump nomenclature （lower camel case）： The first word begins with a lowercase letter ; The first letter of the second word is capitalized , for example ： myName、aDog
    • Big hump nomenclature （upper camel case）： The first letter of each word is capital , for example ：FirstName、 LastName
  • Underline separation ： Multiple word names , Write in all lowercase letters , In the middle _ Separate , for example ：first_name、user_name