Swift While和Repeat While循环语句用法

当迭代次数未知时, 将While和Repeat while循环用作for-in循环的替代方法。 while循环执行一组语句, 直到出现错误条件为止。当你不知道迭代次数时, 通常使用此循环。

Swift中有两种类型的循环：

1. while循环
2. 重复While循环

Swift的While循环

Swift while循环在每次传递开始时评估其条件。

句法：

while (TestExpression) {
    // statements
}

在这里, TestExpression是一个布尔表达式。如果是真的

• 在while循环内的语句被执行。
• 并且, 再次对TestExpression求值。

这个过程一直进行到TestExpression的值为假。当TestExpression获得错误条件时, while循环终止。

While循环流程图

例：

var currentLevel:Int = 0, finalLevel:Int = 6
let gameCompleted = true
while (currentLevel <= finalLevel) {
    //play game
    if gameCompleted {
        print("You have successfully completed level \(currentLevel)")
        currentLevel += 1
    }
}
//outside of while loop
print("Terminated! You are out of the game ")

输出

You have successfully completed level 0
You have successfully completed level 1
You have successfully completed level 2
You have successfully completed level 3
You have successfully completed level 4
You have successfully completed level 5
You have successfully completed level 6
Terminated! You are out of the game

在上面的程序中, 执行while循环, 直到条件被评估为false为止, 并在获得false条件后立即终止。