2.21. Go language switch statement

switch statement is used to perform different actions based on different conditions, each case branches are unique and tested one by one from top to bottom until they match.

switch statement is executed from top to bottom until a match is found, and there is no need to add any more after the match break .

By default, the case statement comes with the break statement at the end of the switch , after successful matching, no other case will be executed, the other will not be executed after the match is successful case if we need to execute the following case , you can use the fallthrough .

2.21.1. Grammar #

The syntax of the switch statement in the Go programming language is as follows:

switch var1 {
    case val1:
        ...
    case val2:
        ...
    default:
        ...
}

Variable var1 can be any type, val1 and val2 can be any value of the same type. Types are not limited to constants or integers, but must be of the same type; or the end result is an expression of the sametype.

You can test multiple values that may meet the criteria simultaneously, using commas to separate them, such as case val1 , val2 , val3 .

Flow chart:

Example #

package main
import "fmt"
func main() {
   /* Define local variables */
   var grade string = "B"
   var marks int = 90
   switch marks {
      case 90: grade = "A"
      case 80: grade = "B"
      case 50,60,70 : grade = "C"
      default: grade = "D"
   }
   switch {
      case grade == "A" :
         fmt.Printf("excellent!\\n" )
      case grade == "B", grade == "C" :
         fmt.Printf("good\\n" )
      case grade == "D" :
         fmt.Printf("pass\\n" )
      case grade == "F":
         fmt.Printf("fail\\n" )
      default:
         fmt.Printf("poor\\n" );
   }
   fmt.Printf("Your level is %s\\n", grade );
}

The result of the above code execution is:

Excellent!
Your level is A

2.21.2. Type Switch #

The switch statement can also be used to determine the type of variable actually stored in a interface variable.

Type Switch syntax format is as follows:

switch x.(type){
    case type:
       statement(s);
    case type:
       statement(s);
    /* You can define any number of cases */
    default: /* optional */
       statement(s);
}

Example #

package main
import "fmt"
func main() {
   var x interface{}

   switch i := x.(type) {
      case nil:
         fmt.Printf(" Type of x:% T",i)
      case int:
         fmt.Printf("X is an int type")
      case float64:
         fmt.Printf("X is a float64 type")
      case func(int) float64:
         fmt.Printf("X is func (int) type")
      case bool, string:
         fmt.Printf("X is bool or string type" )
      default:
         fmt.Printf("Unknown type")
   }
}

The result of the above code execution is:

Type of x:<nil>

2.21.3. Fallthrough #

Using fallthrough will force the subsequent case statements to be executed, fallthrough will not determine whether the expression result of the next case is true .

Example #

package main
import "fmt"
func main() {
    switch {
    case false:
            fmt.Println("1、case conditional statement is false")
            fallthrough
    case true:
            fmt.Println("2、case conditional statement is true")
            fallthrough
    case false:
            fmt.Println("3、case conditional statement is false")
            fallthrough
    case true:
            fmt.Println("4、case conditional statement is true")
    case false:
            fmt.Println("5、ccase conditional statement is false")
            fallthrough
    default:
            fmt.Println("6、default case")
    }
}

The result of the above code execution is:

The case conditional statement is true
Case conditional statement is false
The case conditional statement is true

As you can see from the output of the above code: switch judging from the first, the expression is true of case start execution, if case with fallthrough , the program will proceed to the next case and it doesn’t judge the next one, and it will not determine whether the expression of the next case is true .