primes.p8

//  primes.p8
//
//  Original Author:    Dan Jurca
//  Date Created:       1999 November 23
//
//  Update Authors:     Christopher Arnoult
//                      Nicholas Rebhun
//  Last Modified:      2015 June 10
//
//  Does this:
//      prompts user for int nwp; reads int;
//      if int < 1
//          halts
//      else
//          prints first nwp primes.
//  Notice that this program uses all four of the boolean relations on integers; it
//  has nested whiles, a break, an if, and an if-else.
//

{
    int d,n,np,nwp,p;               // nwp is number of wanted primes

    input nwp;
    if ( nwp < 1) {
        return;
    }
    output 2;
    if ( nwp == 1 ) {
        return;
    }
    n = 3;
    output n;
    np = 2;
    while ( np < nwp ) {
        n = n+2;
        d = 3;                      // 1st trial divisor
        p = 1;                      // flag- 1: yes, prime; 0, no
        while ( d*d <= n) {
            if ( d*(n/d) != n ) {
                d = d+2;            // next trial divisor
            } else {
                p = 0;              // n is not a prime
                break;
            }
        }
        if ( p == 1 ) {             // was n prime?
            output n;
            np = np+1;
        }
    }
}