Go — Syntax

Package declaration

Every Go file starts with a package declaration:

package main

import "fmt"

func main() {
    fmt.Println("Hello, World!")
}

Import statements

import "fmt"
import "os"

// Grouped imports
import (
    "fmt"
    "os"
    "strings"
)

// Import with alias
import (
    myfmt "fmt"
    "os"
)

// Blank import (for side effects)
import _ "github.com/lib/pq"

Variables

// var declaration
var name string = "Alice"
var age int

// Short declaration (inside functions only)
name := "Alice"
age := 30

// Multiple declarations
var (
    x int = 10
    y int = 20
)

// Multiple short declarations
x, y := 10, 20

// Blank identifier
_ = someFunction() // Ignore return value

Constants

const Pi = 3.14159
const MaxRetries = 3

// Typed constants
const (
    StatusOK    int = 200
    StatusError int = 500
)

// iota for enumeration
const (
    Sunday = iota // 0
    Monday        // 1
    Tuesday       // 2
    Wednesday     // 3
    Thursday      // 4
    Friday        // 5
    Saturday      // 6
)

// iota with expressions
const (
    _  = iota
    KB = 1 << (10 * iota) // 1024
    MB                    // 1048576
    GB                    // 1073741824
)

Functions

// Basic function
func add(a int, b int) int {
    return a + b
}

// Multiple return values
func divide(a, b float64) (float64, error) {
    if b == 0 {
        return 0, fmt.Errorf("division by zero")
    }
    return a / b, nil
}

// Named return values
func swap(a, b int) (int, int) {
    return b, a
}

// Variadic function
func sum(nums ...int) int {
    total := 0
    for _, n := range nums {
        total += n
    }
    return total
}

Control flow

// if/else
if age >= 18 {
    fmt.Println("Adult")
} else {
    fmt.Println("Minor")
}

// if with init statement
if err := doSomething(); err != nil {
    fmt.Println("Error:", err)
}

// for loop (only loop construct)
for i := 0; i < 5; i++ {
    fmt.Println(i)
}

// while-style
for count < 10 {
    count++
}

// infinite loop
for {
    break
}

// range
for i, v := range []string{"a", "b", "c"} {
    fmt.Println(i, v)
}

// switch
switch day {
case "Monday":
    fmt.Println("Start of week")
case "Friday":
    fmt.Println("Almost weekend")
default:
    fmt.Println("Midweek")
}

// type switch
switch v := i.(type) {
case int:
    fmt.Println("int:", v)
case string:
    fmt.Println("string:", v)
}

Structs

type Person struct {
    Name string
    Age  int
}

// Creation
p1 := Person{Name: "Alice", Age: 30}
p2 := new(Person) // pointer

Methods

func (p Person) Greet() string {
    return "Hello, " + p.Name
}

func (p *Person) SetAge(age int) {
    p.Age = age
}

Error handling

result, err := doSomething()
if err != nil {
    fmt.Println("Error:", err)
    return
}

Mini Practice

Write Go code that:

1. Declares variables with var and :=
2. Creates a function with multiple return values
3. Uses a for loop with range
4. Handles an error with if err != nil

Up Next

In the next lesson, you'll learn about Comments — documenting your Go code.