[Yugong series] go teaching course 006 in July 2022 - automatic derivation of types and input and output

One 、 Automatic derivation type

1. Automatic derivation type

Automatic derivation type , When declaring assignment variables , Unwanted var And variable types , Its type is determined by the assigned value .

package mainimport "fmt"func main() { // initialization  var a int = 10 // assignment  a = 20 // Automatic derivation  b := 30 // Output  fmt.Println(a, b)}

2. summary

• What is automatic derivation type : When declaring assignment variables , Unwanted var And variable types , Its type is determined by the assigned value .
• Automatically deduce the basic syntax format of the type ：“ Variable name := value ”.
• Multiple assignments ( Use the automatic derivation type to assign values to multiple variables at one time ) Grammar format :“ Variable name 1, Variable name 2, Variable name 3:= value 1, value 2, value 3"

Two 、 Input and output

1. Output

1.1 fmt.Print

Normal output

func Print(a ...interface{}) (n int, err error)

• Print Format its parameters in the default format and write them to standard output .
• If two adjacent parameters are not strings , A space is added between their outputs .
• Returns the number of bytes written and any errors encountered .

1.2 fmt.Println

Line feed output

func Println(a ...interface{}) (n int, err error)

• Println Format its parameters in the default format and write them to standard output .
• Spaces are always added between adjacent output parameters and the end of the line breaks .
• Returns the number of bytes written and any errors encountered .

1.3 fmt.Printf

Format output

func Printf(format string, a ...interface{}) (n int, err error)

• Printf according to format Parameter generates a formatted string and writes it to standard output .
• Returns the number of bytes written and any errors encountered .

2. Input

2.1 fmt.Scan

Normal input

func Scan(a ...interface{}) (n int, err error)

• Scan Scan text from standard input , Save the successfully read white space delimited value into the file passed to - The parameters of this function . Line breaks are treated as white space .
• Returns the number of items successfully scanned and any errors encountered . If fewer entries are read than the parameters provided , Will return an error report reason .

Case study ：

package mainimport "fmt"func main() {	var (		name   string		age    int		isMale bool	)	fmt.Scan(&name, &age, &isMale)	fmt.Printf(" Scan results  name:%s age:%d isMarried:%t \n", name, age, isMale)}

2.2 fmt.Scanf

Format input

func Scanf(format string, a ...interface{}) (n int, err error)

• Scanf Scan text from standard input , according to format The format specified by the parameter saves the successfully read blank separated value into the parameter successfully passed to this function .
• Returns the number of items successfully scanned and any errors encountered .

Case study ：

package mainimport "fmt"func main(){	var (		name string		age int		isMale bool	)	fmt.Scanf("name:%s age:%d isMale:%v", &name, &age, &isMale)	//fmt.Scanf("%s%d%t",&name,&age,&isMale) It is recommended that , When typing, use a space between 	fmt.Printf(" Scan results  name:%s age:%d isMarried:%t \n", name, age, isMale)}

2.3 summary

• Scanf() Grammar format :fmt.Scanf("%d",&num)
• Scan() Grammar format :fmt.Scan(&num)
• Variable address : In memory, corresponding storage units will be opened up for variables , In order to find the storage unit access data , The system will add a number to each unit , This number is the address