branch.go

package main

import (
	"fmt"
	"io/ioutil"
)

func eval(a, b int, op string) int {
	var result int
	switch op {
	case "+":
		result = a + b
	case "-":
		result = a - b
	case "*":
		result = a * b
	case "/":
		result = a / b
	default:
		panic("unsupported operator:" + op)
	}
	return result
}

func grade(score int) string {
	g := ""
	switch {
	case score < 0 || score > 100:
		panic(fmt.Sprintf("Wrong score: %d", score))
	case score < 60:
		g = "F"
	case score < 80:
		g = "C"
	case score < 90:
		g = "B"
	case score <= 100:
		g = "A"
	default:
	}
	return g
}

func main() {
	const filename = "abc.txt"
	if contents, err := ioutil.ReadFile(filename); err == nil {
		fmt.Println(string(contents))
	} else {
		fmt.Println("cannot print file contents:", err)
	}
	fmt.Println(eval(1, 2, "+"))
	fmt.Println(
		grade(0),
		grade(59),
		grade(60),
		grade(82),
		grade(99),
		grade(100),
	)
}