calc - the awesome calculator

main.go

// add is tested with a unit test
func add(a, b int) int {
	return a + b
}

// sub is tested by running "calc sub 2 3".
func sub(a, b int) int {
	return a - b
}

// The error paths in main are tested by invoking calc.
func main() {
	if len(os.Args) != 4 {
		fmt.Fprintf(os.Stderr, "expected 3 arguments, got %d\n", len(os.Args)-1)
		exit.Exit(1)
	}

	a, _ := strconv.Atoi(os.Args[2])
	b, _ := strconv.Atoi(os.Args[3])

	var op func(int, int) int
	switch os.Args[1] {
	case "add":
		op = add
	case "sub":
		op = sub
	default:
		fmt.Fprintf(os.Stderr, "unknown operation: %s\n", os.Args[1])
		exit.Exit(1)
	}

	fmt.Println(op(a, b))
}