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C & C++ Multimedia Cyber Classroom
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C and C++ Multimedia Cyber Classroom (Prentice Hall) (1998).iso
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fig20_40.jar
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Ch20
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Fig20_40
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fig20_40.cpp
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C/C++ Source or Header
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1997-11-11
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54 lines
// Fig. 20.40: fig20_40.cpp
// Using a bitset to demonstrate the Sieve of Eratosthenes.
#include <iostream>
#include <iomanip>
#include <bitset>
#include <cmath>
using namespace std;
int main()
{
const int size = 1024;
int i, value, counter;
bitset< size > sieve;
sieve.flip();
// perform Sieve of Eratosthenes
int finalBit = sqrt( sieve.size() ) + 1;
for ( i = 2; i < finalBit; ++i )
if ( sieve.test( i ) )
for ( int j = 2 * i; j < size; j += i )
sieve.reset( j );
cout << "The prime numbers in the range 2 to 1023 are:\n";
for ( i = 2, counter = 0; i < size; ++i )
if ( sieve.test( i ) ) {
cout << setw( 5 ) << i;
if ( ++counter % 12 == 0 )
cout << '\n';
}
cout << endl;
// get a value from the user to determine if it is prime
cout << "\nEnter a value from 1 to 1023 (-1 to end): ";
cin >> value;
while ( value != -1 ) {
if ( sieve[ value ] )
cout << value << " is a prime number\n";
else
cout << value << " is not a prime number\n";
cout << "\nEnter a value from 2 to 1023 (-1 to end): ";
cin >> value;
}
return 0;
}