Download Day 3 - Gloang

Golang
Arrays & Slices
An array is a numbered sequence of elements of a single type, called the element type.
The number of elements is called the length and is never negative
The elements can be addressed by integer indices 0 through len(a)-1
Each element in the arrays is implicitly zeroed
Arrays are values, ex: var a [3]int where a represent the entire array and not a pointer to the
beginning of the arrays.
Go provides built-in functions : len, cap, copy on arrays.
Golang
Arrays & Slices
var a [0]int //array of length 0, useless
var a [3]int //array of length 3
var a [3]int = [3]int{1,2,3} or a := [3]int{1,2,3} //array of length 3
a = new([]int, 10) //creates an array of 10 ints
var a [3]int
a = [3]int{1,2,3}
a = […]int{1,2,3} // creates array of length 3
Golang
Arrays & Slices
Arrays are fixed length, slices are not
slice is reference to a section of array a[1:3], a[:3], a[3:], a[:]
var a []int
a = []int{1,2,3} // slice is of length 3
var a [10]int = []int{1,2,3,4,5,6,7,8,9,0}
b = a[3] => {4}
b = a[3:3] => {}
b = a[3:5] => {4,5}
b = a[3:] => {4,5,6,7,8,9,0}
b = a[:3] => {1,2,3}
Golang
Arrays & Slices
Append – builtin function to append element to an array
a := []int{1,2}
//a has two elements 1,2
a = append(a, 3) //a has three elements 1,2,3
s = make([]int, 3, 5)
s = append(s,4)
s = append(s,5)
s = append(s,6)
// creates a array of length 3 {0,0,0}
// adds a new element 4 {0,0,0,4}
// adds a new element 4 {0,0,0,4}
// adds a new element 4 {0,0,0,4, 5} and capacity increased from 5 to a larger number.
Copy
s := {1,2,3}
var b [5]int
copy (s,b) //copy only copies if b has space
Golang
Arrays
Exercise:
create a array with first 10 even numbers
create a slice from 3rd to 7th element
insert element with value 9 between values 8 and 10 and print the array
slice.(hint: use copy) {8, 9, 10,12}
Extra:
create a append function that detects if we run out of capacity and adds
an element to the array.
Homework:
delete the element you have inserted above.
Golang
Maps
A map is a key-value pair
Key and Value are two different valid go types
Size of map is not fixed like an array
Map is like slice, it is a reference type.
var m map[string]float64
m = map[string]float64{"1":1, "pi":3.1415}
m = make(map[string]float64)
Golang
Maps
Assigning key-value pair
m[“1”] = 2
a := m[“1”]
Delete an entry from the map with specified key.
delete(m,“1”) // deletes and entry
builtins useful are len, copy, make
Golang
Maps
Check existense of a key in the map
value, ok := m[x]
Is ok true/false?
Golang
Maps
Exercise:
Create a map with the following association
Player from a base ball team A
Number of points in the season
Joe
22
Alex
48
Gary
12
Frank
32
Mike
24
Print the map.
Write code to see if Player Mike exists
delete player Mike as he left the team A
check to see if Mike is still associated to team A
Docker Dojo - golang
Complex Arrays and Maps
Two Dimensional Arrays can describe associations
var a [][]string
Maps can be a map of
var a map[string]map[string]int
Map can also have another complex data structure as value
var a map[string][]int
…
Golang
Structures
Struct in Go represents an object.
But unlike any object oriented language, structs in Go do not compose methods
Contains named fields
Structs can have associated methods
type point struct {
x, y float64
}
Structs are values
Structs and their fields can be exported
type Point struct {
x, Y float64
}
Golang
Structures
Struct initialization
Type Point struct {
x, y float64
}
var p Point
p = Point{}
p = Point{2.2,3.3}
p = Point{y:3.3}
pp = new (Point)
(*pp).x = 1.1, pp.y = 2.2
Golang
Structures
Exercise
create a structure rectangle with length and width
create a structure for circle with radius and origin
create a sample instance of both and print their description.
ex: myrectangle has following dimensions, length = 2.0 abd width = 3.0
mycircle has origin at (1, 3.2) and a radius of 3.15
Golang
Structures
Anonymous fields:
type anotherStruct {
x,y int
}
type point struct {
anotherStruct
x, y float64
}
p := point { {1,2}, 1.0, 2.0}
fmt.Println(p.anotherStruct)