Explain the concept of a global variable and its features in a program.

A global variable in Go is a variable declared outside of functions, usually in a package, and accessible throughout the package or even from other packages when exported (with a capital letter).

Features of global variables:

• Initialized when the program starts, before the main execution.
• Have package scope if the name starts with a lowercase letter, or are exported if with an uppercase.
• Used to store state accessible from different functions.
• Can cause issues with concurrent access in multithreaded programs, often requiring synchronization (e.g., using mutex).

Example of a global variable:

package main

import "fmt"

var counter int = 0 // global variable

func increment() {
    counter++
}

func main() {
    increment()
    fmt.Println(counter) // Will print 1
}

Use of global variables should be minimized to avoid complexities in code maintenance and testing.