Learn Go

Thursday, 09/02/2023

Tram Ho

Introduce

In this article, I will rewrite all the knowledge in the process of learning. Get’s go!!!

Declare variable

We have 3 ways to declare variables:

<span class="token number">1</span> . var &lt;name&gt; &lt;type&gt;
   =&gt; var one int; one = <span class="token number">1</span>
        
<span class="token number">2</span> . var &lt;name&gt; = &lt;value&gt;
   =&gt; var one = <span class="token number">1</span>
        
<span class="token number">3</span> . &lt;name&gt; <span class="token operator">:</span> = &lt;value&gt;
   =&gt; one <span class="token operator">:</span> = <span class="token number">1</span>

1 . var <name> <type>

=> var one int; one = 1

2 . var <name> = <value>

=> var one = 1

3 . <name> : = <value>

=> one : = 1

Note: The declaration method 2 and 3 should be used in a function, and the declaration method 1 is often used to declare a global variable for the entire code.

Variables declared but have no value are:

<span class="token number">0</span> for numeric types <span class="token punctuation">,</span>
<span class="token boolean">false</span> for the boolean type <span class="token punctuation">,</span> and
<span class="token string">""</span> (the empty string) for strings.

0 for numeric types ,

false for the boolean type , and

"" (the empty string) for strings.

Use if/else . conditions

<span class="token keyword">if</span> <span class="token operator">&lt;</span> condition expression <span class="token operator">&gt;</span> <span class="token punctuation">{</span>
    <span class="token comment">// implement code</span>
<span class="token punctuation">}</span> <span class="token keyword">else</span> <span class="token keyword">if</span> <span class="token operator">&lt;</span> condition expression <span class="token operator">&gt;</span> <span class="token punctuation">{</span>
    <span class="token comment">// implement code</span>
<span class="token punctuation">}</span> <span class="token keyword">else</span> <span class="token punctuation">{</span>
    <span class="token comment">// implement code</span>
<span class="token punctuation">}</span>

if < condition expression > {

// implement code

} else if < condition expression > {

// implement code

} else {

// implement code

}

If shortened:

<span class="token keyword">func</span> <span class="token function">pow</span> <span class="token punctuation">(</span> x <span class="token punctuation">,</span> n <span class="token punctuation">,</span> lim <span class="token builtin">float64</span> <span class="token punctuation">)</span> <span class="token builtin">float64</span> <span class="token punctuation">{</span>
	<span class="token keyword">if</span> v <span class="token operator">:=</span> math <span class="token punctuation">.</span> <span class="token function">Pow</span> <span class="token punctuation">(</span> x <span class="token punctuation">,</span> n <span class="token punctuation">)</span> <span class="token punctuation">;</span> v <span class="token operator">&lt;</span> lim <span class="token punctuation">{</span>
		<span class="token keyword">return</span> v
	<span class="token punctuation">}</span>
	<span class="token keyword">return</span> lim
<span class="token punctuation">}</span>

func pow ( x , n , lim float64 ) float64 {

if v := math . Pow ( x , n ) ; v < lim {

return v

}

return lim

}

Types of data

bool

string

int  int8  int16  int32  int64
uint uint8 uint16 uint32 uint64 uintptr

byte <span class="token comment">// alias for uint8</span>

rune <span class="token comment">// alias for int32</span>
     <span class="token comment">// represents a Unicode code point</span>

float32 float64

complex64 complex128

bool

string

int int8 int16 int32 int64

uint uint8 uint16 uint32 uint64 uintptr

byte // alias for uint8

rune // alias for int32

// represents a Unicode code point

float32 float64

complex64 complex128

Data type conversion

The expression T(v) converts the value v to type T.

var i int = 42
var f float64 = float64(i)
var u uint = uint(f)

var i int = 42

var f float64 = float64(i)

var u uint = uint(f)

i := 42
f := float64(i)
u := uint(f)

i := 42

f := float64(i)

u := uint(f)

If we declare := like this, the data type will be based on the value of that variable:

i := 42           // int
f := 3.142        // float64
g := 0.867 + 0.5i // complex128

i := 42 // int

f := 3.142 // float64

g := 0.867 + 0.5i // complex128

Function declaration

A function can take zero or more arguments.

Function Returns 1 value:

func add(x int, y int) int {
	return x + y
}

func add(x int, y int) int {

return x + y

}

The function returns multiple values:

func add(x , y int) (int, int) {
	return x, y
}

func add(x , y int) (int, int) {

return x, y

}

For . loop

For:

sum <span class="token operator">:=</span> <span class="token number">0</span>
<span class="token keyword">for</span> i <span class="token operator">:=</span> <span class="token number">0</span> <span class="token punctuation">;</span> i <span class="token operator">&lt;</span> <span class="token number">10</span> <span class="token punctuation">;</span> i <span class="token operator">++</span> <span class="token punctuation">{</span>
	sum <span class="token operator">+=</span> i
<span class="token punctuation">}</span>

sum := 0

for i := 0 ; i < 10 ; i ++ {

sum += i

}

Tiếp tục:

sum <span class="token operator">:=</span> <span class="token number">1</span>
<span class="token keyword">for</span> <span class="token punctuation">;</span> sum <span class="token operator">&lt;</span> <span class="token number">1000</span> <span class="token punctuation">;</span> <span class="token punctuation">{</span>
	sum <span class="token operator">+=</span> sum
<span class="token punctuation">}</span>

sum := 1

for ; sum < 1000 ; {

sum += sum

}

While:

sum <span class="token operator">:=</span> <span class="token number">1</span>
<span class="token keyword">for</span> sum <span class="token operator">&lt;</span> <span class="token number">1000</span> <span class="token punctuation">{</span>
	sum <span class="token operator">+=</span> sum
<span class="token punctuation">}</span>

sum := 1

for sum < 1000 {

sum += sum

}

If you omit the loop condition, it will loop forever.

<span class="token keyword">for</span> <span class="token punctuation">{</span>
<span class="token punctuation">}</span>

for {

}

Switch

Conditional:

<span class="token keyword">import</span> <span class="token punctuation">(</span>
	<span class="token string">"fmt"</span>
	<span class="token string">"runtime"</span>
<span class="token punctuation">)</span>

<span class="token keyword">switch</span> os <span class="token operator">:=</span> runtime <span class="token punctuation">.</span> GOOS <span class="token punctuation">;</span> os <span class="token punctuation">{</span>
	<span class="token keyword">case</span> <span class="token string">"darwin"</span> <span class="token punctuation">:</span>
		fmt <span class="token punctuation">.</span> <span class="token function">Println</span> <span class="token punctuation">(</span> <span class="token string">"OS X."</span> <span class="token punctuation">)</span>
	<span class="token keyword">case</span> <span class="token string">"linux"</span> <span class="token punctuation">:</span>
		fmt <span class="token punctuation">.</span> <span class="token function">Println</span> <span class="token punctuation">(</span> <span class="token string">"Linux."</span> <span class="token punctuation">)</span>
	<span class="token keyword">default</span> <span class="token punctuation">:</span>
		<span class="token comment">// freebsd, openbsd,</span>
		<span class="token comment">// plan9, windows...</span>
		fmt <span class="token punctuation">.</span> <span class="token function">Printf</span> <span class="token punctuation">(</span> <span class="token string">"%s.n"</span> <span class="token punctuation">,</span> os <span class="token punctuation">)</span>
<span class="token punctuation">}</span>

import (

"fmt"

"runtime"

)

switch os := runtime . GOOS ; os {

case "darwin" :

fmt . Println ( "OS X." )

case "linux" :

fmt . Println ( "Linux." )

default :

// freebsd, openbsd,

// plan9, windows...

fmt . Printf ( "%s.n" , os )

}

Unconditional:

<span class="token keyword">import</span> <span class="token punctuation">(</span>
	<span class="token string">"fmt"</span>
	<span class="token string">"time"</span>
<span class="token punctuation">)</span>


t <span class="token operator">:=</span> time <span class="token punctuation">.</span> <span class="token function">Now</span> <span class="token punctuation">(</span> <span class="token punctuation">)</span>
<span class="token keyword">switch</span> <span class="token punctuation">{</span>
<span class="token keyword">case</span> t <span class="token punctuation">.</span> <span class="token function">Hour</span> <span class="token punctuation">(</span> <span class="token punctuation">)</span> <span class="token operator">&lt;</span> <span class="token number">12</span> <span class="token punctuation">:</span>
	fmt <span class="token punctuation">.</span> <span class="token function">Println</span> <span class="token punctuation">(</span> <span class="token string">"Good morning!"</span> <span class="token punctuation">)</span>
<span class="token keyword">case</span> t <span class="token punctuation">.</span> <span class="token function">Hour</span> <span class="token punctuation">(</span> <span class="token punctuation">)</span> <span class="token operator">&lt;</span> <span class="token number">17</span> <span class="token punctuation">:</span>
	fmt <span class="token punctuation">.</span> <span class="token function">Println</span> <span class="token punctuation">(</span> <span class="token string">"Good afternoon."</span> <span class="token punctuation">)</span>
<span class="token keyword">default</span> <span class="token punctuation">:</span>
	fmt <span class="token punctuation">.</span> <span class="token function">Println</span> <span class="token punctuation">(</span> <span class="token string">"Good evening."</span> <span class="token punctuation">)</span>
<span class="token punctuation">}</span>

import (

"fmt"

"time"

)

t := time . Now ( )

switch {

case t . Hour ( ) < 12 :

fmt . Println ( "Good morning!" )

fmt . Println ( "Good afternoon." )

default :

fmt . Println ( "Good evening." )

}

Defer

Defer is a Go feature that allows you to attach a function to execute after the main function completes.

<span class="token keyword">import</span> <span class="token string">"fmt"</span>

<span class="token keyword">func</span> <span class="token function">main</span> <span class="token punctuation">(</span> <span class="token punctuation">)</span> <span class="token punctuation">{</span>
	<span class="token keyword">defer</span> fmt <span class="token punctuation">.</span> <span class="token function">Println</span> <span class="token punctuation">(</span> <span class="token string">"world"</span> <span class="token punctuation">)</span>

	fmt <span class="token punctuation">.</span> <span class="token function">Println</span> <span class="token punctuation">(</span> <span class="token string">"hello"</span> <span class="token punctuation">)</span>
<span class="token punctuation">}</span>

import "fmt"

func main ( ) {

defer fmt . Println ( "world" )

fmt . Println ( "hello" )

}

Stacking defers : are functions called but not yet executed and pushed onto the stack. When the main function completes, functions that haven’t executed it will be run in LIFO (Last-in-First-out) order.

<span class="token keyword">import</span> <span class="token string">"fmt"</span>

<span class="token keyword">func</span> <span class="token function">main</span> <span class="token punctuation">(</span> <span class="token punctuation">)</span> <span class="token punctuation">{</span>
	fmt <span class="token punctuation">.</span> <span class="token function">Println</span> <span class="token punctuation">(</span> <span class="token string">"counting"</span> <span class="token punctuation">)</span>

	<span class="token keyword">for</span> i <span class="token operator">:=</span> <span class="token number">0</span> <span class="token punctuation">;</span> i <span class="token operator">&lt;</span> <span class="token number">10</span> <span class="token punctuation">;</span> i <span class="token operator">++</span> <span class="token punctuation">{</span>
		<span class="token keyword">defer</span> fmt <span class="token punctuation">.</span> <span class="token function">Println</span> <span class="token punctuation">(</span> i <span class="token punctuation">)</span>
	<span class="token punctuation">}</span>

	fmt <span class="token punctuation">.</span> <span class="token function">Println</span> <span class="token punctuation">(</span> <span class="token string">"done"</span> <span class="token punctuation">)</span>
<span class="token punctuation">}</span>

import "fmt"

fmt . Println ( "counting" )

}

fmt . Println ( "done" )

}

summary

So after 1 day I learned:

how to declare variable
if/else statement
data types
function declaration.
For . loop
Switch
Defer, Stacking Defer

Thank you for following my post. Have a nice day. Tks

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Source : Viblo

Learn Go

Introduce

Contents

Declare variable

Use if/else . conditions

Types of data

Data type conversion

Function declaration

For . loop

Switch

Defer

summary

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