demo_calc.go

package trygo

import (
	"bufio"
	"fmt"
	"os"
	"strconv"
)

var reader = bufio.NewReader(os.Stdin)
var st = new(calcstack)

type calcstack struct {
	i    int
	data [10]int
}

func (s *calcstack) push(k int) {
	if s.i+1 > 9 {
		return
	}
	s.data[s.i] = k
	s.i++
}

func (s *calcstack) pop() (ret int) {
	s.i--
	if s.i < 0 {
		s.i = 0
		return
	}
	ret = s.data[s.i]
	return
}

// DemoCalc func
func DemoCalc() {
	for {
		s, err := reader.ReadString('\n')
		var token string
		if err != nil {
			return
		}
		for _, c := range s {
			switch {
			case c >= '0' && c <= '9':
				token = token + string(c)
			case c == ' ':
				r, _ := strconv.Atoi(token)
				st.push(r)
				token = ""
			case c == '+':
				fmt.Printf("%d\n", st.pop()+st.pop())
			case c == '*':
				fmt.Printf("%d\n", st.pop()*st.pop())
			case c == '-':
				p := st.pop()
				q := st.pop()
				fmt.Printf("%d\n", q-p)
			case c == 'q':
				return
			default:
				//error
			}
		}
	}
}