Swift代码在Xcode Playground运行报错，求问题排查与修复

问题 #

Xcode Playground中运行给定Swift代码时触发崩溃，报错信息如下：

error: Execution was interrupted, reason: EXC_BAD_INSTRUCTION (code=EXC_I386_INVOP, subcode=0x0).
__lldb_expr_1/MyPlayground.playground:4: Fatal error: Unexpectedly found nil while unwrapping an Optional value

原代码：

func calculator(a:Int, b:Int) {
  let a = Int(readLine()!)! //First input
  let b = Int(readLine()!)! //Second input

  add(n1: a, n2: b)
  subtract(n1: a, n2: b)
  multiply(n1: a, n2: b)
  divide(n1: a, n2: b)
  
}

//Write your code below this line to make the above function calls work.

func add(n1:Int, n2:Int){
    print(n1+n2)
}

func subtract(n1:Int, n2:Int){
    print(n1-n2)
}
func multiply(n1:Int, n2:Int){
    print(n1*n2)
}
func divide(n1:Int, n2:Int){
    let a1 = Double(n1)
    let a2 = Double(n2)
    print(a1 / a2)
}


calculator(a:3, b:4)

问题根源 #

1. readLine()不兼容Playground环境：Xcode Playground不支持标准输入，readLine()会返回nil，强行用!强制解包必然触发崩溃。
2. 参数冗余覆盖：calculator函数已接收a、b作为入参，但内部又重新定义同名常量，完全忽略传入的参数，属于无效逻辑。

修复代码 #

func calculator(a: Int, b: Int) {
    add(n1: a, n2: b)
    subtract(n1: a, n2: b)
    multiply(n1: a, n2: b)
    divide(n1: a, n2: b)
}

func add(n1: Int, n2: Int) {
    print(n1 + n2)
}

func subtract(n1: Int, n2: Int) {
    print(n1 - n2)
}

func multiply(n1: Int, n2: Int) {
    print(n1 * n2)
}

func divide(n1: Int, n2: Int) {
    // 新增除数非零校验，避免除以0崩溃
    guard n2 != 0 else {
        print("除数不能为0")
        return
    }
    print(Double(n1) / Double(n2))
}

calculator(a: 3, b: 4)

修复说明 #

• 移除函数内的readLine()调用，直接使用传入的参数，匹配函数设计意图。
• 为divide函数增加除数非零判断，避免潜在的除以0错误。
• 运行后输出结果：

  7
  -1
  12
  0.75
  

内容的提问来源于stack exchange，提问作者metomaru