Go Language Notes: Program basics one

This is the fifth day of my participation in the November Gwen Challenge. Check out the details: The last Gwen Challenge 2021

Recently, I have been learning the go language principle and practice with the small volume. Because there is no go language foundation, I followed the rookie tutorial to learn the basic grammar of go language foundation – rookie tutorial. This is the first of two basic notes on go.

Download and install the GO interpreter

https://golang.org/dl/
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1 hello world

hello.go

package main

import "fmt"

func main(a) {
	/* This is my first simple program */
	fmt.Println("Hello, World!")}Copy the code

To run the program

#Methods a
go run hello.go
#Way 2
go bulid hello.go
./hello.exe
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A running program compiled to a different operating system

$ CGO_ENABLED=0 GOOS=linux GOARCH=amd64 go build test.go
$ CGO_ENABLED=0 GOOS=windows GOARCH=amd64 go build test.go
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linux

$ CGO_ENABLED=0 GOOS=darwin GOARCH=amd64 go build test.go
$ CGO_ENABLED=0 GOOS=windows GOARCH=amd64 go build test.go
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windows

$ SET CGO_ENABLED=0SET GOOS=darwin3 SET GOARCH=amd64 go build test.go
$ SET CGO_ENABLED=0 SET GOOS=linux SET GOARCH=amd64 go build  test.go
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2 Data Types

package main

import "fmt"

func main(a) {
	var a bool = true       / / a Boolean
	var b int = 123         / / plastic
	var c float32 = 123.123 // 32-bit floating point type
	// var d byte = 1 // byte
	var ip *int  / / pointer
	var f string / / character
	ip = &b

	f = "Rookie Tutorial"
	fmt.Print(a, b, c, ip, f)
}

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result

true 
123 
123.123 
0xc000012088Novice tutorialCopy the code

Three variables

variable

package main
import "fmt"
func main(a) {

    Declare a variable and initialize it
    var a = "RUNOOB"
    fmt.Println(a)

    // Zero if not initialized
    var b int
    fmt.Println(b)

    // bool Zero is false
    var c bool
    fmt.Println(c)
}
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result

RUNOOB
0
false
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4 constants

const

package main

import "fmt"

func main(a) {
   const LENGTH int = 10
   const WIDTH int = 5  
   var area int
   const a, b, c = 1.false."str" // Multiple assignments

   area = LENGTH * WIDTH
   fmt.Printf("面积为 : %d", area)
   println(a)println(a, b, c)  
}
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result

Area: 50 1 false STRCopy the code

Built-in functions in constant expressions

package main

import "unsafe"
const (
    a = "abc"
    b = len(a)
    c = unsafe.Sizeof(a)
)

func main(a){
    println(a, b, c)
}
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result

abc 3 16
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Iota constant count

/ / instance
package main

import "fmt"

func main(a) {
    const (
            a = iota   / / 0
            b          / / 1
            c          / / 2
            d = "ha"   // ioTA += 1
            e          //"ha" iota += 1
            f = 100    //iota +=1
            g          //100 iota +=1
            h = iota   //7, restore count
            i          / / 8
    )
    fmt.Println(a,b,c,d,e,f,g,h,i)
}
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result

0 1 2 ha ha 100 100 7 8
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5 operators

Arithmetic operator

package main

import "fmt"

func main(a) {

   var a int = 21
   var b int = 10
   var c int

   c = a + b
   fmt.Printf("The value of the first line -c is %d\n", c )
   c = a - b
   fmt.Printf("The value of the second line -c is %d\n", c )
   c = a * b
   fmt.Printf("The value of the third line -c is %d\n", c )
   c = a / b
   fmt.Printf("Line 4 -c has the value %d\n", c )
   c = a % b
   fmt.Printf("The value of line 5 -c is %d\n", c )
   a++
   fmt.Printf("Line 6 - the value of a is %d\n", a )
   a=21   // For testing purposes, a is reassigned to 21
   a--
   fmt.Printf("Line 7 - the value of a is %d\n", a )
}
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result

The value of -c in the first line is 31 in the second line is 11 in the third line is 210 in the fourth line is 2 in the fifth line is 1 in the sixth line is 22 in the seventh line is 20Copy the code

Comparison operator

package main

import "fmt"

func main(a) {
   var a int = 21
   var b int = 10

   if( a == b ) {
      fmt.Printf("The first row - a is equal to b\n")}else {
      fmt.Printf("First line - a does not equal b\n")}if ( a < b ) {
      fmt.Printf("Line 2 - A is less than b\n")}else {
      fmt.Printf("Second line - a is not less than b\n")}if ( a > b ) {
      fmt.Printf("Line 3 - A is greater than b\n")}else {
      fmt.Printf("Line 3 - A is not greater than b\n")}/* Lets change value of a and b */
   a = 5
   b = 20
   if ( a <= b ) {
      fmt.Printf("Line 4 - a is less than or equal to b\n")}if ( b >= a ) {
      fmt.Printf("Row 5 - b is greater than or equal to a\n")}}Copy the code

result

Row 1 minus A is not equal to b row 2 minus A is not less than b row 3 minus A is greater than b row 4 minus A is less than or equal to b row 5 minus b is greater than or equal to aCopy the code

Logical operator

package main

import "fmt"

func main(a) {
   var a bool = true
   var b bool = false
   if ( a && b ) {
      fmt.Printf("First line - condition true\n")}if ( a || b ) {
      fmt.Printf("Second line - condition true\n")}/* Change the values of a and b */
   a = false
   b = true
   if ( a && b ) {
      fmt.Printf("Line 3 - condition true\n")}else {
      fmt.Printf("Line 3 - condition false\n")}if ( !(a && b) ) {
      fmt.Printf("Line 4 - condition true\n")}}Copy the code

result

Line 2 - condition true line 3 - condition false line 4 - condition trueCopy the code

An operator

package main

import "fmt"

func main(a) {

   var a uint = 60      /* 60 = 0011 1100 */  
   var b uint = 13      /* 13 = 0000 1101 */
   var c uint = 0          

   c = a & b       /* 12 = 0000 1100 */
   fmt.Printf("The value of the first line -c is %d\n", c )

   c = a | b       /* 61 = 0011 */
   fmt.Printf("The value of the second line -c is %d\n", c )

   c = a ^ b       /* 49 = 0011 0001 */
   fmt.Printf("The value of the third line -c is %d\n", c )

   c = a << 2     /* 240 = 1111 0000 */
   fmt.Printf("Line 4 -c has the value %d\n", c )

   c = a >> 2     /* 15 = 0000 1111 */
   fmt.Printf("The value of line 5 -c is %d\n", c )
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result

The value of -c in the first line is 12 the value of -c in the second line is 61 the value of -c in the third line is 49 the value of -C in the fourth line is 240 and the value of -c in the fifth line is 15Copy the code

The assignment operator

package main

import "fmt"

func main(a) {
   var a int = 21
   var c int

   c =  a
   fmt.Printf("Line 1 - = operator instance, c value = %d\n", c )

   c +=  a
   fmt.Printf("Line 2 - += operator instance, c value = %d\n", c )

   c -=  a
   fmt.Printf("Line 3 -= operator instance, c value = %d\n", c )

   c *=  a
   fmt.Printf("Line 4 - *= operator instance, c value = %d\n", c )

   c /=  a
   fmt.Printf("Line 5 - /= operator instance, c value = %d\n", c )

   c  = 200;

   c <<=  2
   fmt.Printf("Line 6 - <<= operator instance, c value = %d\n", c )

   c >>=  2
   fmt.Printf("Line 7 - >>= operator instance, c value = %d\n", c )

   c &=  2
   fmt.Printf("Line 8 - &= operator instance with c value = %d\n", c )

   c ^=  2
   fmt.Printf("Line 9 - ^= operator instance, c value = %d\n", c )

   c |=  2
   fmt.Printf("Line 10 - | = operator as an example, the value of c = % d \ n", c )

}
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result

Line 1 -= operator instance, c value = 21 Line 2 - += operator instance, C value = 42 Line 3 - -= operator instance, c value = 21 line 4 - *= operator instance, Line 6 - <<= instance of the operator, line 7 - >>= instance of the operator, line 8 - &= instance of the operator, line 7 - >>= instance of the operator, line 8 - &= instance, Value of c = 0 line 9 - ^ = operator instance, c = 2 value line 10 - | = operator as an example, the value of c = 2Copy the code

Other operators

package main

import "fmt"

func main(a) {
   var a int = 4
   var b int32
   var c float32
   var ptr *int

   /* Operator instance */
   fmt.Printf("Line 1 - a variable of type = %T\n", a );
   fmt.Printf("Line 2 -b variable type = %T\n", b );
   fmt.Printf("Line 3 -c variable type = %T\n", c );

   The /* & and * operator instances */
   ptr = &a     /* 'PTR' contains the address of the 'a' variable */
   fmt.Printf("Value of a is %d\n", a);
   fmt.Printf("* PTR for % d \ n", *ptr);
}
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result

Line 1 -a variable type = int Line 2 -b variable type = int32 Line 3 -C variable type = float32 The value of A is 4 * PTR is 4Copy the code

Operator priority

package main

import "fmt"

func main(a) {
   var a int = 20
   var b int = 10
   var c int = 15
   var d int = 5
   var e int;

   e = (a + b) * c / d;      // (30 * 15) / 5
   fmt.Printf("(a + b) * c/d = %d\n",  e );

   e = ((a + b) * c) / d;    // (30 * 15) / 5
   fmt.Printf("((a + b) * c)/d = %d\n" ,  e );

   e = (a + b) * (c / d);   / / (30) * (15/5)
   fmt.Printf("(a + b) * (c/d) = %d\n",  e );

   e = a + (b * c) / d;     //  20 + (150/5)
   fmt.Printf("A + (b * c)/d = %d\n" ,  e );  
}
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result

The value of (a + b) * c/d is 90. The value of (a + b) * c/d is 90. The value of (a + b) * (c/d) is 90Copy the code

6 Conditional Statements

If the else statement

package main

import "fmt"

func main(a) {
   /* Local variable definition */
   var a int = 100;
 
   /* Determine the Boolean expression */
   if a < 20 {
       /* If the condition is true, the following statement */ is executed
       fmt.Printf("A less than 20 \ n" );
   } else {
       /* If the condition is false, the following statement */ is executed
       fmt.Printf("A not less than 20\n" );
   }
   fmt.Printf("A value is: %d\n", a);

}
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result

A is not less than 20. The value of a is 100Copy the code

A switch statement

/ / instance
package main

import "fmt"

func main(a) {
   /* 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("Good! \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 );      
}
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result

Excellent! You're an ACopy the code

// Example 2 Type Switch
package main

import "fmt"

func main(a) {
   var x interface{}
     
   switch i := x.(type) {
      case nil:  
         fmt.Printf(" x 的类型 :%T",i)                
      case int:  
         fmt.Printf("X is int")                      
      case float64:
         fmt.Printf("X is float64")          
      case func(int) float64:
         fmt.Printf("X is of type func(int)")                      
      case bool.string:
         fmt.Printf("X is a bool or string" )      
      default:
         fmt.Printf("Unknown type")}}Copy the code

result

Type of x :<nil>Copy the code

// Example 3 fallthrough
package main

import "fmt"

func main(a) {

    switch {
    case false:
            fmt.Println("1, case condition statement false")
            fallthrough
    case true:
            fmt.Println("2, case condition statement true")
            fallthrough
    case false:
            fmt.Println("3, case condition statement false")
            fallthrough
    case true:
            fmt.Println("4, case condition statement true")
    case false:
            fmt.Println("5, case condition statement false")
            fallthrough
    default:
            fmt.Println("6. Default case")}}Copy the code

result

The case condition statement is set to true. The case condition statement is set to falseCopy the code

The select statement

package main

import "fmt"

func main(a) {
   var c1, c2, c3 chan int
   var i1, i2 int
   select {
      case i1 = <-c1:
         fmt.Printf("received ", i1, " from c1\n")
      case c2 <- i2:
         fmt.Printf("sent ", i2, " to c2\n")
      case i3, ok := (<-c3):  // same as: i3, ok := <-c3
         if ok {
            fmt.Printf("received ", i3, " from c3\n")}else {
            fmt.Printf("c3 is closed\n")}default:
         fmt.Printf("no communication\n")}}Copy the code

result

no communication
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7 Loop Statements

The for loop

/ / instance
package main

import "fmt"

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

55
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2 / / instance
package main

import "fmt"

func main(a) {
        sum := 1
        for ; sum <= 10; {
                sum += sum
        }
        fmt.Println(sum)

        // Write it like this, more like a While statement
        for sum <= 10{
                sum += sum
        }
        fmt.Println(sum)
}
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result

16
16
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// Example three wireless loop
package main

import "fmt"

func main(a) {
        sum := 0
        for {
            sum++ // Go on forever
        }
        fmt.Println(sum) // Cannot output
}
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result

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Break to terminate
Continue skips the current loop and proceeds to the next round
Goto goes to the marker

/ / instance goto
package main

import "fmt"

func main(a) {
   /* Define local variables */
   var a int = 10

   / * * / cycles
   LOOP: for a < 20 {
      if a == 15 {
         /* Skip the iteration */
         a = a + 1
         goto LOOP
      }
      fmt.Printf("A value is: %d\n", a)
      a++    
   }  
}
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result

The value of a is: 10. The value of A is: 11. The value of A is: 12. The value of A is: 13. The value of A is: 14Copy the code

8 Language Functions

package main

import "fmt"

func main(a) {
   /* Define local variables */
   var a int = 100
   var b int = 200
   var ret int

   /* Call the function and return the maximum value */
   ret = max(a, b)

   fmt.Printf( "Maximum value: %d\n", ret )
}

/* Returns the maximum value of two numbers */
func max(num1, num2 int) int {
   /* Define local variables */
   var result int

   if (num1 > num2) {
      result = num1
   } else {
      result = num2
   }
   return result
}
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result

The maximum value is 200Copy the code

Return multiple values

package main

import "fmt"

func swap(x, y string) (string.string) {
   return y, x
}

func main(a) {
   a, b := swap("Google"."Runoob")
   fmt.Println(a, b)
}
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result

Runoob Google
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Scope of language variables

package main

import "fmt"

/* Declare the global variable */
var a int = 20;

func main(a) {
   /* Declare a local variable */ in the main function
   var a int = 10
   var b int = 20
   var c int = 0

   fmt.Printf("main()函数中 a = %d\n",  a);
   c = sum( a, b);
   fmt.Printf("main()函数中 c = %d\n",  c);
}

/* Function definition - Add two numbers */
func sum(a, b int) int {
   fmt.Printf("Sum () a = %d\n",  a);
   fmt.Printf("In sum() b = %d\n",  b);

   return a + b;
}
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result

A is equal to 10 in the main() function and sum() is equal to 20 in the sum() function and c is equal to 30 in the main() functionCopy the code

Go Language Notes: Program basics one

1 hello world

2 Data Types

Three variables

4 constants

5 operators

6 Conditional Statements

7 Loop Statements

8 Language Functions

Scope of language variables

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