So far the program executed steps in order. Today it learns to choose.

if / else. The condition is any bool value:

if it.Pages > 300 {
	fmt.Println("A thick book")
} else if it.Pages > 100 {
	fmt.Println("Medium")
} else {
	fmt.Println("Thin")
}

Boolean operators combine conditions: && (and), || (or), ! (not):

if it.Read && it.Pages > 300 { ... }   // read AND thick
if it.Pages < 50 || !it.Read { ... }   // thin OR not read

switch. When you compare one value against many options, an if chain becomes a staircase — switch is cleaner:

switch choice {
case "1":
	printItem(it)
case "2":
	fmt.Println("Marked.")
default:
	fmt.Println("Unknown choice.")
}

Go's switch stops by itself after each case — no break needed (unlike C). default is the "nothing matched" branch: exactly the one that will catch bad input.