Typical C language example: Prime Number judgment

Prime number. In a natural number greater than 1, except for 1 and the integer itself, it cannot be divisible by other natural numbers.

Basic version _ bool isprimer (unsigned N) {If (n <= 1) return false; unsigned I, TEM = SQRT (n) + 1; for (I = 2; I <= TEM; I ++)/* 2 is also a prime number */If (N % I = 0) return false; return true;} upgraded version _ bool isprimer (unsigned N) {If (n = 2) return true; If (n <= 1 | n % 2 = 0) return false; even numbers other than/* 2 are not prime numbers */unsigned I, TEM = SQRT (n) + 1; for (I = 3; I <= TEM; I + = 2) /* I = 2 has been judged before. Here, it starts from 3 and returns false with an odd number */If (N % I = 0; /* and the N entered here is an odd number, and the odd number cannot be divisible by an even number. Therefore, I increase by 2 */return true ;}

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