Golang Programming Examples

Go Nil slice

golang

package main

import "fmt"

func main() {
   var numbers []int
   printSlice(numbers)
   
   if(numbers == nil){
      fmt.Printf("slice is nil")
   }
}
func printSlice(x []int){
   fmt.Printf("len = %d cap = %d slice = %v\n", len(x), cap(x),x)
}

Go len() and cap() functions

golang

package main

import "fmt"

func main() {
   var numbers = make([]int,3,5)
   printSlice(numbers)
}
func printSlice(x []int){
   fmt.Printf("len=%d cap=%d slice=%v\n",len(x),cap(x),x)
}

Go Pointers to Structures

golang

package main

import "fmt"

type Books struct {
   title string
   author string
   subject string
   book_id int
}
func main() {
   var Book1 Books   /* Declare Book1 of type Book */
   var Book2 Books   /* Declare Book2 of type Book */
 
   /* book 1 specification */
   Book1.title = "Go Programming"
   Book1.author = "Mahesh Kumar"
   Book1.subject = "Go Programming Tutorial"
   Book1.book_id = 6495407

   /* book 2 specification */
   Book2.title = "Telecom Billing"
   Book2.author = "Zara Ali"
   Book2.subject = "Telecom Billing Tutorial"
   Book2.book_id = 6495700
 
   /* print Book1 info */
   printBook(&Book1)

   /* print Book2 info */
   printBook(&Book2)
}
func printBook( book *Books ) {
   fmt.Printf( "Book title : %s\n", book.title);
   fmt.Printf( "Book author : %s\n", book.author);
   fmt.Printf( "Book subject : %s\n", book.subject);
   fmt.Printf( "Book book_id : %d\n", book.book_id);
}

Go Structures as Function Arguments

golang

package main

import "fmt"

type Books struct {
   title string
   author string
   subject string
   book_id int
}
func main() {
   var Book1 Books    /* Declare Book1 of type Book */
   var Book2 Books    /* Declare Book2 of type Book */
 
   /* book 1 specification */
   Book1.title = "Go Programming"
   Book1.author = "Mahesh Kumar"
   Book1.subject = "Go Programming Tutorial"
   Book1.book_id = 6495407

   /* book 2 specification */
   Book2.title = "Telecom Billing"
   Book2.author = "Zara Ali"
   Book2.subject = "Telecom Billing Tutorial"
   Book2.book_id = 6495700
 
   /* print Book1 info */
   printBook(Book1)

   /* print Book2 info */
   printBook(Book2)
}
func printBook( book Books ) {
   fmt.Printf( "Book title : %s\n", book.title);
   fmt.Printf( "Book author : %s\n", book.author);
   fmt.Printf( "Book subject : %s\n", book.subject);
   fmt.Printf( "Book book_id : %d\n", book.book_id);
}

Go Accessing Structure Members

golang

package main

import "fmt"

type Books struct {
   title string
   author string
   subject string
   book_id int
}
func main() {
   var Book1 Books    /* Declare Book1 of type Book */
   var Book2 Books    /* Declare Book2 of type Book */
 
   /* book 1 specification */
   Book1.title = "Go Programming"
   Book1.author = "Mahesh Kumar"
   Book1.subject = "Go Programming Tutorial"
   Book1.book_id = 6495407

   /* book 2 specification */
   Book2.title = "Telecom Billing"
   Book2.author = "Zara Ali"
   Book2.subject = "Telecom Billing Tutorial"
   Book2.book_id = 6495700
 
   /* print Book1 info */
   fmt.Printf( "Book 1 title : %s\n", Book1.title)
   fmt.Printf( "Book 1 author : %s\n", Book1.author)
   fmt.Printf( "Book 1 subject : %s\n", Book1.subject)
   fmt.Printf( "Book 1 book_id : %d\n", Book1.book_id)

   /* print Book2 info */
   fmt.Printf( "Book 2 title : %s\n", Book2.title)
   fmt.Printf( "Book 2 author : %s\n", Book2.author)
   fmt.Printf( "Book 2 subject : %s\n", Book2.subject)
   fmt.Printf( "Book 2 book_id : %d\n", Book2.book_id)
}

Go Passing pointers to functions

golang

package main

import "fmt"

func main() {
   /* local variable definition */
   var a int = 100
   var b int= 200

   fmt.Printf("Before swap, value of a : %d\n", a )
   fmt.Printf("Before swap, value of b : %d\n", b )

   /* calling a function to swap the values.
   * &a indicates pointer to a ie. address of variable a and 
   * &b indicates pointer to b ie. address of variable b.
   */
   swap(&a, &b);

   fmt.Printf("After swap, value of a : %d\n", a )
   fmt.Printf("After swap, value of b : %d\n", b )
}
func swap(x *int, y *int) {
   var temp int
   temp = *x    /* save the value at address x */
   *x = *y      /* put y into x */
   *y = temp    /* put temp into y */
}

Go - Pointer to pointer

golang

package main

import "fmt"

func main() {
   var a int
   var ptr *int
   var pptr **int

   a = 3000

   /* take the address of var */
   ptr = &a

   /* take the address of ptr using address of operator & */
   pptr = &ptr

   /* take the value using pptr */
   fmt.Printf("Value of a = %d\n", a )
   fmt.Printf("Value available at *ptr = %d\n", *ptr )
   fmt.Printf("Value available at **pptr = %d\n", **pptr)
}

Go Array of pointers

golang

package main

import "fmt"
 
const MAX int = 3
 
func main() {
   a := []int{10,100,200}
   var i int

   for i = 0; i < MAX; i++ {
      fmt.Printf("Value of a[%d] = %d\n", i, a[i] )
   }
}

Nil Pointers in Go

golang

package main

import "fmt"

func main() {
   var  ptr *int

   fmt.Printf("The value of ptr is : %x\n", ptr  )
}

Go How to Use Pointers

golang

package main

import "fmt"

func main() {
   var a int = 20   /* actual variable declaration */
   var ip *int      /* pointer variable declaration */

   ip = &a  /* store address of a in pointer variable*/

   fmt.Printf("Address of a variable: %x\n", &a  )

   /* address stored in pointer variable */
   fmt.Printf("Address stored in ip variable: %x\n", ip )

   /* access the value using the pointer */
   fmt.Printf("Value of *ip variable: %d\n", *ip )
}

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