[Yugong series] July 2022 go teaching course 019 - for circular structure

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One 、 Loop structure

1. What is cycle

Loop structure refers to a program structure that needs to perform a function repeatedly in a program . It is by the conditions in the circulatory body , Determine whether to continue a function or exit the loop . According to the judgment condition , The circular structure can be subdivided into the following two forms : The loop structure of judgment before execution and the loop structure of execution before judgment .

2.Go The cycle in

stay Go The structure format of the loop in the language is as follows :

for  The initial statement ; Conditional expression ; The end of the statement  {
    
   Loop body code 
}

for The cycle will go on and on , Until the conditional expression returns false Just launch the cycle , The perform for loop “}” Later code .

3. Basic use of recycling

package main

import "fmt"

func main() {
    
	for i := 0; i < 100; i++ {
    
		fmt.Println("100 A foolish man ")
	}
}

The initial statement can also be ignored without writing , But the semicolon after the initial statement must be written , The code is as follows :

package main

import "fmt"

func main() {
    
	i := 0
	for ; i < 100; i++ {
    
		fmt.Println("100 A foolish man ")
	}
}

The code above will i On the for Initialize before the loop , At this time i The scope of is not limited to for Within the loop .

4. The use of dead circulation

sum := 0
for {
    
    sum++
    if sum > 100 {
    
        break
    }
}

5. Case study

package main

import "fmt"

func main() {
    

    //  Traverse ,  Decide what line to deal with 
    for y := 1; y <= 9; y++ {
    

        //  Traverse ,  Decide how many columns there are in this row 
        for x := 1; x <= y; x++ {
    
            fmt.Printf("%d*%d=%d ", x, y, x*y)
        }

        //  Manually generate carriage returns 
        fmt.Println()
    }
}

Two 、break sentence

Go In language break Statements can end for、switch and select Code block for , in addition break Statements can also be tagged after statements , Indicates to exit the code block corresponding to a tag , Label requirements must be defined in the corresponding for、switch and select On the code block of .

1. Out of the loop

package main

import "fmt"

func main()  {
    
	//  Outer loop 
	for i := 0; i < 10; i++ {
    
		fmt.Printf("i: %d\n", i)

		//  When  i  be equal to  6  when , Jump to loop 
		if i == 6 {
    
			//  Out of the loop 
			break
		}
	}

	fmt.Println(" Out of the loop  ...")
}

2. Jump out of label code block

package main

import "fmt"

func main() {
    

OuterLoop:
    for i := 0; i < 2; i++ {
    
        for j := 0; j < 5; j++ {
    
            switch j {
    
            case 2:
                fmt.Println(i, j)
                break OuterLoop
            case 3:
                fmt.Println(i, j)
                break OuterLoop
            }
        }
    }
}

3、 ... and 、continue sentence

Go In language continue Statement can end the current loop , Start the next iteration of the loop , Only in for Use in cycle , stay continue When you add a label after a statement , Represents the loop corresponding to the start tag .

1. Start the next cycle

package main

import "fmt"

func main()  {
    

	for i := 0; i < 10; i++ {
    
		//  When  i  be equal to  2  when , perform  continue  sentence , So let's go to the next loop 
		if i == 2 {
    
			continue
		}

		fmt.Printf("i: %d\n", i)
	}
}

2. Start label code cycle

package main

import "fmt"

func main() {
    

OuterLoop:
    for i := 0; i < 2; i++ {
    

        for j := 0; j < 5; j++ {
    
            switch j {
    
            case 2:
                fmt.Println(i, j)
                continue OuterLoop
            }
        }
    }

}