eval-add-times.scala

/**
 * Evaluate simple math expressions, supports add/times.
 * Operator precedence is observed.
 * e.g. in the expression 5+3*2, 3*2 would be evaluated first, leading to the final result of 11.
 */
def eval(expr: String): Int = {
    var i = 0
    var result = 0
    var num = 0
    while (i < expr.size) {
      expr(i) match {
        case '*' =>
          i = i + 1
          var num2 = 0
          while (i < expr.size && expr(i) != '+' && expr(i) != '*') {
            num2 = (num2 * 10) + expr(i).asDigit
            i = i + 1
          }
          num = num * num2
        case '+' =>
          result = result + num
          num = 0
          i = i + 1
        case c =>
          num = (num * 10) + c.asDigit
          i = i + 1
      }
    }
    result + num
  }