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Closed 9 years ago.

我对阵列感到不安。我用一本书复制了该法典:

#include <stdio.h>
#include <stdbool.h>

int main (void)
{
    int     p, i, primes[50], primeIndex = 2;
    bool    isPrime;

    primes[0] = 2;
    primes[1] = 3;

    for (p = 5; p <= 50; p = p + 2) {
        isPrime = true;

        for (i = 1; isPrime && p / primes[i] >= primes[i]; ++i)
            if (p % primes[i] == 0)
                isPrime = false;

        if (isPrime == true) {
            primes[primeIndex] = p;
            ++primeIndex;
        }
    }

    for (i = 0; i < primeIndex; ++i)
        printf ("%i ", primes[i]);

    printf ("
");

    return 0;
}

我尤其难以理解<代码>primeIndex与i变量之间的区别。 <代码>primeIndex系指阵列编号和i系指阵列中的数字。权利?

Answer 1

primeIndex is the place where the next found prime is written in the prime array, and also the number of primes known so far. i is the index of the prime used for trial division. For each candidate, i loops from 1 (we don t need to try out primes[0] = 2 because only odd numbers are checked) to the index of the first prime larger than the square root of the candidate.

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