swift - 如何在Swift中更改变量时更新字符串

抱歉，这个非常初学者的问题...我正在学习编码Swift。
我正在定义一个变量，然后根据其值打印条件消息。当我将变量更改为另一个值时，我希望消息字符串会更改，但不会更改。我究竟做错了什么？
这是代码：

//: Playground - noun: a place where people can play

import Cocoa

var str = "Hello, playground"


var townname = "Azadinos"
var population: Int = 5422
var message: String
var Haspostoffice: Bool = true

if population < 10000 {
        message = "with a population of \(population), \(townname) is a small town"
} else if population >= 10000 && population < 15000 {
        message = "with a population of \(population), \(townname) is a medium sized town!"
}else {message = "\(townname) is a huge town!"}

print (message)

population = 250000

print (population)

print(message)

我希望第二个消息与第一个消息不同，但是没有。我究竟做错了什么？
非常感谢

最佳答案

您应该通过Swift Documentation中的String Interpolation

String interpolation通过将string的值包含在constants, variables, literals, and expressions中，可以帮助您从string literal的混合组合中输入新的why it is not updating for second message值。例如上面的文档：

let multiplier = 3 //This is constant
let message = "\(multiplier) times 2.5 is \(Double(multiplier) * 2.5)"
// message prints :   "3 times 2.5 is 7.5"

这是您的工作代码：

var townname = "Azadinos"
var population: Int = 5422
var message: String
var Haspostoffice: Bool = true

if population < 10000 {
   message = "with a population of \(population), \(townname) is a small town"
} else if population >= 10000 && population < 15000 {
   message = "with a population of \(population), \(townname) is a medium sized town!"
} else {
   message = "\(townname) is a huge town!"
}

print (message)
population = 250000
print (population)
print(message)

现在作为问题if-else，您应该编写一个函数，然后对变量进行更改。因为您的代码以单流程运行，所以在最后一行开始和结束。您的variable(message)条件不知道if-else是否发生变化。因此，如果您希望这种情况发生，则必须在修改message变量后再次编写function条件，或者只是创建message并在更改后调用该函数。如果有意义，请看下面的代码。尝试以不同的方式编写函数。

var townname = "Azadinos"
var population: Int = 5422
var message = ""
var Haspostoffice: Bool = true

func printMyVars() {
    if population < 10000 {
        message = "with a population of \(population), \(townname) is a small town"
    } else if population >= 10000 && population < 15000 {
        message = "with a population of \(population), \(townname) is a medium sized town!"
    } else {
        message = "\(townname) is a huge town!"
    }
    print(message)
}
printMyVars()
population = 250000
printMyVars()

打印：

with a population of 5422, Azadinos is a small town
Azadinos is a huge town!

关于swift - 如何在Swift中更改变量时更新字符串，我们在Stack Overflow上找到一个类似的问题：https://stackoverflow.com/questions/38066226/