Question 22: Determine whether a number is a prime number

/*************************************** *
* *** AUTHER: liuyongshui
* ****** DATE: 2013 \ 4 \ 7
* ** LANGUAGE: C
* ** QUESTION: determines whether a number is a prime number.
****************************************/

# Include <stdio. h>

Int main ()
{
Int I;
Int num;
Int flag = 1; // flag

Printf ("enter an integer greater than 1 (This number must be large ):");
Scanf ("% d", & num );

If (num = 2)
{
Flag = 1;
}
Else
{
For (I = 2; I <= num/2; I ++)
{
If (num % I = 0) // if it is not a prime number, num/I! = 0, and vice versa is equal to zero
{
Flag = 0;
Break; // if it is not a prime number, end the judgment.
}
}
}

If (flag)
{
Printf ("% d is a prime number \ n", num );
}
Else
{
Printf ("% d is not a prime number \ n", num );
}

Return 0;
}