C language to determine whether a number is prime __c language

The so-called prime is the number of numbers that cannot be divisible by any other integer except 1 and itself.

To judge a number n (n>=3) method: N as dividend, will be 2 to (n-1) each integer divisor, if all can not be divisible, then n is prime.

Algorithm Analysis:

S1: Enter value for n

s2:i=2 (i as divisor)

S3:n by I, the remainder r,r=0, which means that n can be divisible by I, then N is not prime, the algorithm ends.

s4:i=i+1 if i<=n-1, returns S3, otherwise n is prime.

Code:

#include <stdio.h>


int main (void)
{
int i,j;
int temp;
scanf ("%d", &i);
for (j=2;j<=i-1;j++)
{
if (i%j==0)
{
printf ("not prime. \ n");
return 0;
}


}
printf ("is prime. \ n");
return 0;
}

Improvement: In fact, N does not need to be divided by 2 to (n-1) integers, only divisible by 2 to N/2, or even divisible by 2 to (n^ (1/2)). If I<=SQRT (n), returns S3, otherwise the algorithm ends.

Code

#include <stdio.h>


int main (void)
{
int i,j;
int temp;
scanf ("%d", &i);
for (j=2;j<=i-1;j++)
{
if (i%j==0)
{
printf ("not prime. \ n");
return 0;
}


}
printf ("is prime. \ n");
return 0;
}