C # search for prime numbers

I have learned some methods to search for prime numbers before I learned C. The conventional method seems to be inefficient. Recently I found a "delete method" on the Forum to search for prime numbers, the space complexity is much lower, with less repeated execution, but no execution steps required. It is a class about searching for prime numbers from 0 to n. It starts from 1.1 drops of programming.

Class prime
　　
{
　　
Public static int [] primelist;
　　
Public static void findprime (int n)
　　
{
　　
Int [] intlist;
　　
Intlist = new int [N];
　　
For (int p = 2; P <= N; P ++) intlist [P-1] = P; // assign 2 to n to this array
　　
For (int p = 2; P <math. SQRT (n); P ++)
　　
{
　　
Int J = p + 1;
　　
While (j <= N)
　　
{
　　
If (intlist [J-1]! = 0) & (intlist [J-1] % P) = 0) intlist [J-1] = 0; // determine if the element is not a prime number and assign the value to zero
　　
J = J + 1;
　　
}
　　
}
　　
Int I = 0;
　　
For (int p = 2; P <= N; P ++)
　　
{
　　
If (intlist [P-1]! = 0)

I = I + 1; // we can see that all elements that are not prime numbers are assigned 0; the number of elements that are not 0 is counted, that is, the number of prime numbers from 0 to n.
　　
}
　　
Primelist = new int [I]; // creates an array to store prime numbers.
　　
I = 0;
　　
For (int p = 2; P <= N; P ++)
　　
{
　　
If (intlist [P-1]! = 0) // so far, the element not zero in the array is a prime number,
　　
{
　　
Primelist [I] = intlist [P-1]; // store the prime number in the array.
　　
I = I + 1;
　　
}
　　
}
　　
}
　　
}

The so-called deletion method is to assign a number to zero if it is determined that it is not a prime number during the test. It can also be understood as indirect search for prime numbers, which is easier than direct search.

Learning Programming starts from 1.1 drops ..