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C > 05. Functions I [PROGRAM #07]
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```/* Problem: Write a program that prints out all the
prime numbers between 1 and a set limit (1000 in this example). */

#include <stdio.h>
#include <math.h>
#define LIMIT 1000

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

/* function returns true if n is prime */
int
prime3 (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=1;
}
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 sqrt(n)      */
for (i=3; i<=sqrt(n); i=i+2)
{
if (!(n%i))
divisor=i;
}
}

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

}

/* This main program prints all prime numbers
between 1 and the set limit */

int
main (void)
{
int x;

for (x=1; x<=LIMIT; ++x)
if (prime3 (x))
printf (" %d ", x);

return (0);
}
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