Carbon条件语句 #

var score: i32 = 85;

if (score >= 60) {
  Print("及格");
}

var score: i32 = 45;

if (score >= 60) {
  Print("及格");
} else {
  Print("不及格");
}

var score: i32 = 85;

if (score >= 90) {
  Print("优秀");
} else if (score >= 80) {
  Print("良好");
} else if (score >= 70) {
  Print("中等");
} else if (score >= 60) {
  Print("及格");
} else {
  Print("不及格");
}

var age: i32 = 25;
var has_license: bool = true;

if (age >= 18) {
  if (has_license) {
    Print("可以驾驶");
  } else {
    Print("需要考取驾照");
  }
} else {
  Print("年龄不够");
}

var score: i32 = 85;
var result: String = if score >= 60 then "及格" else "不及格";
Print("{0}", result);

var score: i32 = 85;
var grade: String = 
  if score >= 90 then "A"
  else if score >= 80 then "B"
  else if score >= 70 then "C"
  else if score >= 60 then "D"
  else "F";
Print("等级: {0}", grade);

var x: i32 = 10;
var result: i32 = if x > 0 then {
  var doubled: i32 = x * 2;
  doubled
} else {
  0
};

var day: i32 = 3;

match (day) {
  case 1 => Print("星期一");
  case 2 => Print("星期二");
  case 3 => Print("星期三");
  case 4 => Print("星期四");
  case 5 => Print("星期五");
  case 6 => Print("星期六");
  case 7 => Print("星期日");
  default => Print("无效的日期");
}

var day: i32 = 3;
var name: String = match (day) {
  case 1 => "星期一";
  case 2 => "星期二";
  case 3 => "星期三";
  case 4 => "星期四";
  case 5 => "星期五";
  case 6 => "星期六";
  case 7 => "星期日";
  default => "无效";
};
Print("{0}", name);

var day: i32 = 6;

match (day) {
  case 1 or 2 or 3 or 4 or 5 => Print("工作日");
  case 6 or 7 => Print("周末");
  default => Print("无效");
}

var score: i32 = 85;

match (score) {
  case 90..100 => Print("优秀");
  case 80..89 => Print("良好");
  case 70..79 => Print("中等");
  case 60..69 => Print("及格");
  case 0..59 => Print("不及格");
  default => Print("无效分数");
}

var value: i32 = 42;

match (value) {
  case x if x > 100 => Print("大于100: {0}", x);
  case x if x > 50 => Print("大于50: {0}", x);
  case x => Print("其他: {0}", x);
}

var point: (i32, i32) = (10, 20);

match (point) {
  case (0, 0) => Print("原点");
  case (x, 0) => Print("X轴上: {0}", x);
  case (0, y) => Print("Y轴上: {0}", y);
  case (x, y) => Print("坐标: ({0}, {1})", x, y);
}

var value: Optional(i32) = Some(42);

match (value) {
  case Some(x) => Print("值: {0}", x);
  case None => Print("无值");
}

interface Shape {
  fn Area(me) -> f64;
}

class Circle {
  var radius: f64;
  impl Shape {
    fn Area(me) -> f64 { return 3.14159 * me.radius * me.radius; }
  }
}

class Rectangle {
  var width: f64;
  var height: f64;
  impl Shape {
    fn Area(me) -> f64 { return me.width * me.height; }
  }
}

fn Describe(s: Shape) -> String {
  return match (s) {
    case c: Circle => "圆形，面积: {0}".Format(c.Area());
    case r: Rectangle => "矩形，面积: {0}".Format(r.Area());
  };
}

var x: i32 = 15;

match (x) {
  case n if n < 0 => Print("负数");
  case n if n == 0 => Print("零");
  case n if n < 10 => Print("小于10的正数");
  case n if n < 100 => Print("两位数");
  default => Print("大于等于100");
}

var age: i32 = 25;
var has_id: bool = true;

match ((age, has_id)) {
  case (a, true) if a >= 18 => Print("成年人，有证件");
  case (a, false) if a >= 18 => Print("成年人，无证件");
  case (_, _) => Print("未成年人");
}

enum State {
  Idle,
  Running,
  Paused,
  Stopped
}

fn HandleEvent(state: State, event: Event) -> State {
  return match ((state, event)) {
    case (State.Idle, Event.Start) => State.Running;
    case (State.Running, Event.Pause) => State.Paused;
    case (State.Running, Event.Stop) => State.Stopped;
    case (State.Paused, Event.Resume) => State.Running;
    case (State.Paused, Event.Stop) => State.Stopped;
    case (s, _) => s;  // 保持当前状态
  };
}

fn Divide(a: i32, b: i32) -> Optional(i32) {
  return if b == 0 then None else Some(a / b);
}

var result: Optional(i32) = Divide(10, 2);
match (result) {
  case Some(value) => Print("结果: {0}", value);
  case None => Print("除数不能为零");
}

fn ParseCommand(cmd: String) -> Command {
  return match (cmd.ToLower()) {
    case "help" => Command.Help;
    case "exit" => Command.Exit;
    case "list" => Command.List;
    case s if s.StartsWith("get ") => Command.Get(s[4..]);
    case s if s.StartsWith("set ") => Command.Set(s[4..]);
    default => Command.Unknown(cmd);
  };
}

// 推荐：使用match
match (status) {
  case 0 => Print("成功");
  case 1 => Print("失败");
  case 2 => Print("待处理");
  default => Print("未知状态");
}

// 不推荐：if-else链
if (status == 0) {
  Print("成功");
} else if (status == 1) {
  Print("失败");
} else if (status == 2) {
  Print("待处理");
} else {
  Print("未知状态");
}

// 好的做法：覆盖所有情况
enum Color { Red, Green, Blue }

fn ToHex(c: Color) -> String {
  return match (c) {
    case Color.Red => "#FF0000";
    case Color.Green => "#00FF00";
    case Color.Blue => "#0000FF";
  };
}

// 好的做法
var is_valid: bool = age >= 18 and has_license;
if (is_valid) {
  Print("可以驾驶");
}

// 避免
if (age >= 18 and has_license) {
  Print("可以驾驶");
}

var x: i32 = 100;
match (x) {
  case 1 => Print("一");
  case 2 => Print("二");
  // 遗漏default，x=100时无匹配
}

var score: i32 = 85;

// 错误：顺序不对
if (score >= 60) {
  Print("及格");
} else if (score >= 80) {  // 永远不会执行
  Print("良好");
}

// 正确：从高到低
if (score >= 80) {
  Print("良好");
} else if (score >= 60) {
  Print("及格");
}

var x: i32 = 10;

// 错误：使用赋值
// if (x = 10) { ... }

// 正确：使用比较
if (x == 10) {
  Print("等于10");
}