Thread: This C code finds primes.....compiled TinyC

Code:

/* 
This program is used to find prime numbers greater than 5. 
*/
#include <stdio.h>


int main() 
{
                                                                /* largest unsigned long long int is 18,446,744,073,709,551,615, around 2^64 – 1 */
    unsigned long long int n, i=3, count, c, half;                /* n is the number of total primes to find     */
                                                                /* count is the number of primes found thus far */ 
                                                                /* i is the starting number of primes computed    */ 
                                                                /* c is the factoring number             */
                                                
                                                
                                                
                                                
                                                
    
    printf("Enter the number of primes to be found:");
    scanf("%d" , &n);
    
    if (n >= 1) 
    {
        while (i < 5)
        {
            printf("Enter the starting number to evaluate equal or greater than 5:"); // i first number ot evaluate
            scanf("%d" , &i);
            if (i<3) {i=3;}             /* makes sure the first factor is 3 */
        }


        printf("First %d prime numbers equal or greater than 5:\n" ,n);
        if    (i==3) { printf("2\n"); }
        n++;
    }
    
    for ( count = 2; count <= n; )                 /* This counts the number of primes searched for in *count* */
    {
        // half=(i/3)+1;                        // This WAS an optimization entry.        
        for (c = 2; c <= half; c++)                // increments the divisor.
        {
            if (i%c == 0)                        // finds the primes if they are divisable.
            break;
            half=(i/c)+1;                        // This IS an optimization entry.
        }
        if (1)                                    
        {
            printf("%d  ", i);
            count++;
            if ((count-2)%4==0) printf("\n");   // counts 4 numbers written and prints a \n return long long unsigned in fits 4 per page.
        }
        i++;                                      // it is over here that counts UP.
    }        
    return 0;
}