[Yugong series] July 2022 go teaching course 017 - if of branch structure

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Preface

if Conditional statement is an important programming statement , It is used to tell the program to execute a certain program when a certain condition is true , In another case, another statement is executed .

One 、IF sentence

1.IF Basic use of sentences

Go In language ,if else The format of condition judgment is as follows ：

if  expression 1 {
    
   Branch 1
} else if  expression 2 {
    
   Branch 2
} else {
    
   Branch 3
}

• When the expression 1 As the result of the true when , Will take branches 1 Code for .
• When the expression 1 As the result of the false when , Will execute expression 2, If the result is true, Branches will be taken 2 Code for .
• When the previous conditions are not met , That is to say, all are false when , Will take branches 3 Code for .

Related cases ：

package main

import "fmt"

func main() {
    
	//  Define a string 
	str := 10

	//  Judge whether the length of the string is equal to 14
	if str == 10 {
    
		//  If it is equal to the 14
		fmt.Println(" Yu Gong is equal to 10 year ")
	} else {
    
		//  If not equal to 14
		fmt.Println(" Yu Gong is not equal to 10 year ")
	}
}

package main

import "fmt"

func main() {
    
	var userName string
	var userPwd string
	fmt.Println(" Please enter a user name :")
	fmt. Scan (&userName)
	fmt.Println(" Please input a password :")
	fmt.Scan (&userPwd)
	//2: Verify the user name and password , If the user name and password are entered correctly , give " You can log in to the system "
	if userName == "admin" && userPwd == "88888"{
    
		fmt.Println(" You can log in to the system ")
	}else if userName == "admin" {
    
		fmt. Println(" Wrong password ")
	} else if userPwd == "88888" {
    
		fmt.Println(" User name error !!")
	}else {
    
		fmt.Println(" Then the account name and password are entered incorrectly !!")
	}
}

2.IF Special writing of sentences

if There is also a special way of writing , We can do it in if Add an execution statement before the expression , Then judge according to the variables , The code is as follows ：

if err := Connect(); err != nil {
    
	fmt.Println(err)
	return
}

Connect() Is a function to obtain database connection , It has a return value ,err := Connect() Is a statement , perform Connect() After the function , Assign errors to err Variable .

err != nil yes if The conditional expression of , When err Isn't empty , Print the error and return .