Functions

        
          package main

import "fmt"

// Function with parameters and return value
func add(a, b int) int {
    return a + b
}

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

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

// Anonymous function
func counter() func() int {
    count := 0
    return func() int {
        count++
        return count
    }
}

// Struct definition
type Person struct {
    Name string
    Age  int
}

// Method (function attached to a type)
func (p Person) Greet() string {
    return fmt.Sprintf("Hello, I'm %s", p.Name)
}

// Pointer receiver method (can modify the struct)
func (p *Person) Birthday() {
    p.Age++
}

// Interface definition
type Speaker interface {
    Speak() string
}

// Implement interface
func (p Person) Speak() string {
    return fmt.Sprintf("My name is %s and I'm %d years old", p.Name, p.Age)
}

// Function that accepts interface
func introduce(s Speaker) {
    fmt.Println(s.Speak())
}

// Generic function (Go 1.18+)
func printSlice[T any](slice []T) {
    for _, item := range slice {
        fmt.Printf("%v ", item)
    }
    fmt.Println()
}

// Main function demonstrating usage
func main() {
    // Basic function calls
    result := add(5, 3)
    fmt.Printf("5 + 3 = %d\n", result)

    // Multiple return values
    quotient, err := divide(10, 2)
    if err != nil {
        fmt.Println("Error:", err)
    } else {
        fmt.Printf("10 / 2 = %.2f\n", quotient)
    }

    // Variadic function
    total := sum(1, 2, 3, 4, 5)
    fmt.Printf("Sum: %d\n", total)

    // Closure
    increment := counter()
    fmt.Println(increment()) // 1
    fmt.Println(increment()) // 2

    // Methods
    person := Person{Name: "John", Age: 25}
    fmt.Println(person.Greet())

    person.Birthday()
    fmt.Printf("After birthday: %d years old\n", person.Age)

    // Interface
    introduce(person)

    // Generics
    numbers := []int{1, 2, 3, 4, 5}
    names := []string{"Alice", "Bob", "Charlie"}

    printSlice(numbers)
    printSlice(names)
}