stride与循环结构

区间运算符
开区间：[a,b]
闭区间：[a,b)
举例：
1.开区间

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for index in 1..<10{
    index;
}

index的值一次为:0~9;可以用此方法遍历数组。比如：

var scoreArr = [22,33,44,55,66,77,88,99];
var count = scoreArr.count;
for index in 0 ..< count{
    var s = scoreArr[index];
    print(s);
}

2.闭区间

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for index in 1...10{
    index;
}

index的值以此为：0~10

在swift3.0中stride语法已经改为这样:stride(from: , to: , by: )函数和stride(from: , through: , by: )函数

stride 方法定义在 Strideable 协议中,swift3.0废弃了传统C的for循环之后，定义的全新方法。
stride(from: , to: , by: )相当于开区间；
stride(from: , through: , by: )相当于闭区间
个人理解：
表示从初始数值到目标数值,by:表示跨越的进度（可加可减）。
举例：

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for index in stride(from: 10, through: 0, by: -1){
    print(index);
}

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for index in stride(from: 10, to: 0, by: -1){
    print(index);
}

index的数值:
index –10
index –9
index –8
index –7
index –6
index –5
index –4
index –3
index –2
index –1

用stride方法遍历scoreArr数组

for i in stride(from: 0, to: scoreArr.count, by: 1){
    var arr = scoreArr[i];
    print(arr);
}