// EvaluateExpression evaluates a arithmetic expression and returns the result value.
func EvaluateExpression(e string) (int, error) {
e += "#" // used as terminated symbol
operator := list.NewStack(false, false, true)
operator.Push("#")
operand := list.NewStack(false, false, true)
for !operator.Empty() {
c := ""
if len(e) != 0 {
c = string(e[0])
}
if c != "+" && c != "-" && c != "*" && c != "/" && c != "(" && c != ")" && c != "#" && c != "" {
operand.Push(c)
} else {
opt, _ := operator.Top()
switch operandPrecede(opt.(string), c) {
case 1:
operator.Pop()
b, _ := operand.Top()
operand.Pop()
a, _ := operand.Top()
operand.Pop()
r, err := operate(a.(string), opt.(string), b.(string))
if err != nil {
return 0, err
}
operand.Push(r)
continue
case 0:
operator.Pop()
case -1:
operator.Push(c)
}
}
if len(e) >= 2 {
e = e[1:len(e)]
}
}
r, err := operand.Top()
if err != nil {
return 0, err
}
r, err = strconv.Atoi(r.(string))
if err != nil {
return 0, err
}
return r.(int), err
}
// MatchQuotationMark checks whether input quotation marks is pair-matched.
func MatchQuotationMark(q string) bool {
s := list.NewStack(false, false, true)
for len(q) != 0 {
m := string(q[0])
t, err := s.Top()
if err != nil {
s.Push(m)
} else {
if t == "[" && m == "]" {
s.Pop()
} else if t == "(" && m == ")" {
s.Pop()
} else if t == "{" && m == "}" {
s.Pop()
} else {
s.Push(m)
}
}
q = q[1:len(q)]
}
if !s.Empty() {
return false
}
return true
}
// NumeralConversion converts i (positive) from one numeral base to another.
func NumeralConversion(fromBase, toBase int, i string) (string, error) {
s := list.NewStack(false, false, true)
pow := 1
iTenBase := 0
for len(i) != 0 {
num, err := strconv.Atoi(i[len(i)-1 : len(i)])
if err != nil {
return "", err
}
iTenBase += (num * pow)
pow *= fromBase
i = i[0 : len(i)-1]
}
for iTenBase != 0 {
s.Push(iTenBase % toBase)
iTenBase /= toBase
}
var buffer bytes.Buffer
for !s.Empty() {
v, _ := s.Top()
buffer.WriteString(strconv.Itoa(v.(int)))
s.Pop()
}
return buffer.String(), nil
}