private static readonly List<long> KnownPrimes = new List<long>() { 2, 3, 5, 7};
static void Main(string[] args)
{
int numDivisors;
string input = "";
bool first = true;
while (!int.TryParse(input, out numDivisors))
{
if(!first) Console.WriteLine("You must enter a number with no other characters.");
Console.WriteLine("Find the least common multiple for numbers 1 through:");
input = Console.ReadLine();
first = false;
}
int index = -1;
//make sure that there are enough primes in the list
while (index == -1)
{
index = KnownPrimes.FindIndex(n => n > numDivisors);
if(index == -1) AppendNextPrime();
}
// prep the list with 0s
List<int> countPrimes = KnownPrimes.Select(n=>0) as List<int>;
當我在 Rider 中除錯最后一行時，它顯示：
Enumerable.Select() returned: Count = 5 countPrimes: null
從我讀過的內容來看，LINQ 不應該能夠回傳空值，而且它似乎不是，但不知何故，變數仍然是空值。我顯然在這里遺漏了一些東西，誰能幫我確定我做錯了什么？
uj5u.com熱心網友回復：
as 運算子將回傳 null，因為 Select 的結果不是List<int>，而是IEnumerable<int>. 將其替換ToList為從 IEnumerable 中創建一個串列：
List<int> countPrimes = KnownPrimes.Select(n=>0).ToList();
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