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C > 05. Functions I [PROGRAM #06]
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```/* Function finding prime numbers (no pointers) */
#include <stdio.h>
#include <math.h>

/* function returns true if n is even.  */
/* it returns false if n is odd         */
int
even (int n)
{
return (n%2==0);
}

/* function returns true if n is prime */
int
prime (int n)
{
int divisor, i;

/* looking for a divisor. if found, it
is not a prime number */

divisor = 0;

/* eliminating even numbers except 2 */
if (even (n))
{
if (n == 2)
divisor = 0;
else
divisor = 2;
}
else
{
if (n == 1)
divisor = 0; /* 1 is a prime number */
else
/* trying to divide number by 3,5,7,... */
/* to find a divisor until we reach n-1      */
for (i = 3; i < n; i = i + 2)
{
if (n % i == 0)
divisor = i;
}
}

/* if there is a divisor (not zero) then NOT prime */
return (!divisor);
}

int
main (void)
{
int x;

printf ("Enter a positive integer number: ");
scanf ("%d", &x);

/*  testing for prime and printing the report */
if (prime (x))
printf ("%d is a prime number.\n", x);
else
printf ("%d is not a prime number.\n", x);

return (0);
}
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```Enter a positive integer number: 59