（7） Loop statement for

1 for keyword

1.1 Standard writing

and C Linguistic for equally ：

for init; condition; post {
     }

• init： It's usually an assignment expression , Assign initial values to control variables ;
• condition： A relational or logical expression , Cycle control conditions ;
• post： It's usually an assignment expression , Increment or decrement of a control variable .

example ： Calculation 1 To 10 The sum of the numbers ：

package main

import "fmt"

func main() {
    
        sum := 0
        for i := 0; i <= 10; i++ {
    
                sum += i
        }
        fmt.Println(sum)
}

1.2 And C Language while similar

and C Of while equally ：

for condition {
     }

example ： stay sum Less than 10 When the sum The value after self adding

package main

import "fmt"

func main() {
    
        sum := 1

        //  It's OK to write like this , More like  While  Statements in the form of 
        for sum <= 10{
    
                sum ++
        }
        fmt.Println(sum)
}

1.3 Infinite loop

and C Of for(; equally ：

for {
     }

example ： Infinite loop

package main

import "fmt"

func main() {
    
        sum := 0
        for {
    
            sum++ //  Go on indefinitely 
        }
        fmt.Println(sum) //  Unable to output 
}

1.4 Statements that jump out of the loop

• break： Jump out of the loop .
• continue： Jump out of a cycle .

1.5 Composite types use for-each range loop

For-each range loop

The loop in this format can be used for string 、 Array 、 Slice and so on to iterate the output elements .

package main
import "fmt"

func main() {
    
        strings := []string{
    "google", "runoob"}
        for i, s := range strings {
    
                fmt.Println(i, s)
        }


        numbers := [6]int{
    1, 2, 3, 5}
        for i,x:= range numbers {
    
                fmt.Printf(" The first  %d  position  x  Value  = %d\n", i,x)
        }  
}

The output of the above example is :：

0 google
1 runoob
 The first  0  position  x  Value  = 1
 The first  1  position  x  Value  = 2
 The first  2  position  x  Value  = 3
 The first  3  position  x  Value  = 5
 The first  4  position  x  Value  = 0
 The first  5  position  x  Value  = 0

for Cyclic range The format can be omitted key and value, The following example ：

package main
import "fmt"

func main() {
    
    map1 := make(map[int]float32)
    map1[1] = 1.0
    map1[2] = 2.0
    map1[3] = 3.0
    map1[4] = 4.0
   
    //  Read  key  and  value
    for key, value := range map1 {
    
      fmt.Printf("key is: %d - value is: %f\n", key, value)
    }

    //  Read  key
    for key := range map1 {
    
      fmt.Printf("key is: %d\n", key)
    }

    //  Read  value
    for _, value := range map1 {
    
      fmt.Printf("value is: %f\n", value)
    }
}

The output of the above example is :

key is: 4 - value is: 4.000000
key is: 1 - value is: 1.000000
key is: 2 - value is: 2.000000
key is: 3 - value is: 3.000000
key is: 1
key is: 2
key is: 3
key is: 4
value is: 1.000000
value is: 2.000000
value is: 3.000000
value is: 4.000000