c# - Check if number is prime number -

i ask if correct way of checking if number prime or not? because read 0 , 1 not prime number.

int num1;  console.writeline("accept number:"); num1 = convert.toint32(console.readline()); if (num1 == 0 || num1 == 1) {     console.writeline(num1 + " not prime number");     console.readline(); } else {     (int = 2; <= num1 / 2; a++)     {         if (num1 % == 0)         {             console.writeline(num1 + " not prime number");             return;         }      }     console.writeline(num1 + " prime number");     console.readline(); } 

var num1;  console.writeline("accept number:"); num1 = convert.toint32(console.readline()); if(isprime(num1)) {   console.writeline("it prime"); } else {   console.writeline("it not prime"); }         public static bool isprime(int number) {     if (number == 1) return false;     if (number == 2) return true;     if (number % 2 == 0)  return false;      var boundary = (int)math.floor(math.sqrt(number));      (int = 3; <= boundary; i+=2)     {         if (number % == 0)  return false;     }      return true;         } 

i changed number / 2 math.sqrt(number) because in wikipedia, said:

this routine consists of dividing n each integer m greater 1 , less or equal square root of n. if result of of these divisions integer, n not prime, otherwise prime. indeed, if n = a*b composite (with , b ≠ 1) 1 of factors a or b @ square root of n