我正在使用Erastosthenes方法的筛选器,以便打印所有素数最多为1000的程序。程序正在运行,但由于某种原因程序不会删除组合的数字。由于我的程序运行,我确信它只是一个逻辑错误,并且该错误在我的identifyPrimes函数中,但我一直无法找到它。为什么我的程序不能识别素数?
#include <cstdlib>
#include <iostream>
using namespace std ;
void initializeNumbers (char number[], int ARRAY_SIZE)
{
number[0] = 'I' ; // 'I' means Ignore
number[1] = 'I' ;
for (int i = 2 ; i < ARRAY_SIZE ; i ++)
number[i] = 'U' ;
/* --------------------------------------------------------
Function indexOfLeastU returns the least index such that
the character stored at that index is 'U', with the
exception that -1 is returned if no array element has
value 'U'.
-------------------------------------------------------- */
int indexOfLeastU (char number[], int ARRAY_SIZE)
{
for (int i = 0 ; i < ARRAY_SIZE ; i ++)
if (number[i] == 'U')
return i ;
return -1 ;
} // end indexOfLeastU function
/* --------------------------------------------------------
Function identifyPrimes identifies which numbers are
prime by placing 'P's at those indices.
Composite #'s are marked with 'C's.
-------------------------------------------------------- */
void identifyPrimes (char number[], int ARRAY_SIZE)
{
int leastU = indexOfLeastU (number, ARRAY_SIZE) ;
while (leastU >= 0)
{
number [leastU] = 'P' ; // 'P' for Prime
// mark multiples as Composite ...
for (int i = (2 * leastU) ; i < ARRAY_SIZE ; i += leastU)
number [leastU] = 'C' ; // 'C' for Composite
leastU = indexOfLeastU (number, ARRAY_SIZE) ;
} // end while loop
} // end identifyPrimes function
/* --------------------------------------------------------
Function printPrimes prints those array indices whose
corresponding elements have the value 'P'.
-------------------------------------------------------- */
void printPrimes (char number[], int ARRAY_SIZE)
{
// print the indices at which a 'P' is stored ...
cout << "\nThe prime numbers up to 1000 are:\n\n" ;
for (int i = 0 ; i < ARRAY_SIZE ; i ++)
if (number[i] == 'P')
cout << i << '\t' ;
cout << endl << endl ;
} // end printPrimes function
int main ()
{
// declare & initialize constants ...
const int MAX_NUMBER = 1000 ;
const int ARRAY_SIZE = MAX_NUMBER + 1 ;
// declare array ...
char number [ ARRAY_SIZE ] = { '\0' } ;
initializeNumbers (number, ARRAY_SIZE) ;
identifyPrimes (number, ARRAY_SIZE) ;
printPrimes (number, ARRAY_SIZE) ;
system("pause");
} // end main function
你的括号不均衡,有没有密切的'initializeNumbers的()'函数。 – Barmar
你应该习惯于在'if',''while','for'等身体周围放置'{...}',即使在主体中只有一个语句。 – Barmar
这是一个非常复杂的代码,用于实现筛选。该算法非常简单,我几乎不能理解你的代码。您可以在输出上打印整个表格,这可能有助于发现错误。 – luk32