如何生成一个随机运算符，将其放入字符串中，并评估该字符串

Question

I'm trying to build an equation that takes random operators.

3 x 5 x 8 x 2

where x represents either a +, -, / * operator.

2nd question: if the equation is a string, can golang evaluate the answer?

(this question is for this problem http://www.reddit.com/r/dailyprogrammer/comments/1k7s7p/081313_challenge_135_easy_arithmetic_equations/ )

Answer 1

Generating a random operator is straightforward:

    rand.Seed(int64(time.Now().Unix()))
    op := "+-/*"[rand.Intn(4)]
    fmt.Printf("%c
", op)

(that's math/rand)

Evaluating simple expressions in the format suggested is also easy. Here is a simplistic, inefficient, and fragile way of doing it:

expr := strings.Fields("4 * 8 / 2 * 3")
fmt.Printf("%#v
", expr)

do := func(i int, op func(a, b int) int) {
    ai, err := strconv.Atoi(expr[i-1])
    check(err)
    bi, err := strconv.Atoi(expr[i+1])
    check(err)
    expr[i-1] = strconv.Itoa(op(ai, bi))
    expr = append(expr[:i], expr[i+2:]...)
    fmt.Printf("%#v
", expr)
}

for _, ops := range []string{"*/", "+-"} {
    for i := 0; i < len(expr); i++ {
        if strings.Contains(ops, expr[i]) {
            switch expr[i] {
            case "*": do(i, func(a, b int) int { return a*b })
            case "/": do(i, func(a, b int) int { return a/b })
            case "+": do(i, func(a, b int) int { return a+b })
            case "-": do(i, func(a, b int) int { return a-b })
            }
            i -= 2
        }
    }
}

fmt.Println(expr[0])

(runnable on http://play.golang.org/p/pITy4SgXaA)

Making it not break down with improper expressions and handle non-ints is left as an exercise for the reader.

As a side note, these kinds of challenges are generally meant as entertainment for the developer. Asking here means you're transferring that fun to somebody else.