Go program prints asterisks instead of actual characters

I'm writing a program that converts postfix expression to it's prefix form (so like it should convert this "ABC/-AK/L-*" to this "*-A/BC-/AKL". The rules are simple: if it's a letter or a number (operand), then it is pushed to the stack, if it's an operator, then two lasts characters (let's say op1(the last) and op2(the one after the last one)) of the stack are being popped and then concatenated with the operator (temp = operator + op2 + op1) and this temp is then pushed to the stack.

The issue is that when pop is used operands become asterisks and I don't know why. Perhaps pointers are needed? Could someone please tell me what am I doing wrong? Thank you very much!

input: "ABC/-AK/L-*"

expected output: "*-A/BC-/AKL"

observed output: "[***]"

import (
	"fmt"
)

type Stack []string

func (s *Stack) isEmpty() bool {
	return len(*s) == 0
}

func (s *Stack) push(value string) {
	*s = append(*s, value)
}

func (s *Stack) pop() (string, bool) {
	if s.isEmpty() {
		return "", false
	} else {
		elementIndex := len(*s) - 1
		element := (*s)[elementIndex]
		*s = (*s)[:elementIndex]
		return element, true
	}
}

func isOperator(character string) bool {
	switch character {
	case "+", "-", "*", "/":
		return true
	default:
		return false
	}

}

func input() {
	var stack Stack
	fmt.Print("Please input the equation without spaces: \n")
	input := "ABC/-AK/L-*"


	for _, character := range input {
		valueCheck := isOperator(string(character))
		if valueCheck == true {
			operand1 := input[len(input)-1]
			stack.pop()
			operand2 := input[len(input)-1]
			stack.pop()

			var temp string
			temp = string(character) + string(operand2) + string(operand1)
			stack.push(temp)

		} else {
			stack.push(string(character))
		}
	}

	fmt.Print(stack)

}

func main() {
	input()
}



</details>


# 答案1
**得分**: 0

```go
func input() {
    var stack Stack
    fmt.Print("请输入没有空格的方程式：\n")
    input := "ABC/-AK/L-*"

    for _, character := range input {
        valueCheck := isOperator(string(character))
        if valueCheck {
            operand1 := stack[len(stack)-1]
            stack.pop()
            operand2 := stack[len(stack)-1]
            stack.pop()

            temp := string(character) + string(operand2) + string(operand1)
            stack.push(temp)
        } else {
            stack.push(string(character))
        }
    }
}

这段代码会按照你的期望给出结果。

还有几点注意事项：
1）if valueCheck == true 太冗余了，因为 valueCheck 是布尔类型。
2）var temp string 和 temp = string(character) + string(operand2) + string(operand1) 有点啰嗦，可以简化为 temp := string(character) + string(operand2) + string(operand1)。

最好熟悉一下 dlv 调试器，这样下次遇到问题时可以节省时间和精力。

func input() {
    var stack Stack
    fmt.Print("Please input the equation without spaces: \n")
    input := "ABC/-AK/L-*"


    for _, character := range input {
        valueCheck := isOperator(string(character))
        if valueCheck {
            operand1 := stack[len(stack)-1]
            stack.pop()
            operand2 := stack[len(stack)-1]
            stack.pop()


            temp := string(character) + string(operand2) + string(operand1)
            stack.push(temp)

        } else {
            stack.push(string(character))
        }
    }

var temp string
temp = string(character) + string(operand2) + string(operand1)

temp := string(character) + string(operand2) + string(operand1)