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1.GRIDDLE METHOD (ALSO CALLED SIFT METHOD)
When I was a student in Bachelor phrase , a teacher has tought me a method called griddle method , it's principle is:
if a number can be devided by another number(except 1) , it isn't a prime , so , we set the non-prime at zero. after all number [In fact , half of the range checked is OK ]test finished , We simply output the NON-ZERO number , it 's the prime table in the RANGE.
E.G
Define the Range from 1-100;
/********************************************************************
created: 2007/04/19
created: 19:4:2007 3:00
filename: C:\testvc6\TestStll\TestStll.cpp
file path: C:\testvc6\TestStll
file base: TestStll
file ext: cpp
author: Chang xinglong(King.C)
purpose: Print Prime Table in RANGE(1-100)
*********************************************************************/
created: 2007/04/19
created: 19:4:2007 3:00
filename: C:\testvc6\TestStll\TestStll.cpp
file path: C:\testvc6\TestStll
file base: TestStll
file ext: cpp
author: Chang xinglong(King.C)
purpose: Print Prime Table in RANGE(1-100)
*********************************************************************/
The Code Here :
#include <iostream>#include <algorithm>#include <vector>using namespace std;void InitArray(int A[] ,int len)
{
for (int i=0;i<len;i++)
{ A[i]=i+1;
}
}void OutputPrime(int A[] ,int len){ for (int i=2;i<len;i++) { for (int j=2;i*j<=len;j++) { A[i*j-1]=0; cout<<i<<","<<j<<","<<i*j<<endl; } } for (i=0;i<len;i++) { if (A[i]!=0) { cout<<A[i]<<" "; } } cout<<endl;}// Main Method [4/19/2007 Changxinglong (King.C)]int main(int argc, char* argv[]){ int A[100]; InitArray(A,100); OutputPrime(A,100); return 1;} 2.THE DIRECT METHOD
E.G
/********************************************************************
created: 2007/04/19
created: 19:4:2007 3:00
filename: C:\testvc6\TestStll\TestStll.cpp
file path: C:\testvc6\TestStll
file base: TestStll
file ext: cpp
author: Chang xinglong(King.C)
purpose: Prime ?
*********************************************************************/
created: 2007/04/19
created: 19:4:2007 3:00
filename: C:\testvc6\TestStll\TestStll.cpp
file path: C:\testvc6\TestStll
file base: TestStll
file ext: cpp
author: Chang xinglong(King.C)
purpose: Prime ?
*********************************************************************/
Here is the Kernel Function(Quote : STL TURORIAL REFERRENCE):
1//predicate, which returns whether an integer is a prime number
2bool isPrime (int number)
3{
4//ignore negative sign
5number = abs(number);
6// 0 and 1 are prime numbers
7if (number == 0 || number == 1) {
8return true;
9}
10//find divisor that divides without a remainder
11int divisor;
12for (divisor = number/2; number%divisor != 0; --divisor) {
13;
14}
15//if no divisor greater than 1 is found, it is a prime number
16return divisor == 1;
17}
//predicate, which returns whether an integer is a prime number2
bool isPrime (int number)3
{4
//ignore negative sign5
number = abs(number);6
// 0 and 1 are prime numbers7
if (number == 0 || number == 1) {8
return true;9
}10
//find divisor that divides without a remainder11
int divisor;12
for (divisor = number/2; number%divisor != 0; --divisor) {13
;14
}15
//if no divisor greater than 1 is found, it is a prime number16
return divisor == 1;17
}
In Main Function , traverse the given range judge every number use the above function:
int main(int argc , char * argv[]){ int A[100]; InitArray(A,100); for(int i=0;i<100;i++) if(isPrime(A[i])) cout<<A[i]<<endl;}3. Extention
Further , if there is a given List or Vector and it's filled with data , how can you find the prime number in the data effiectly ?
STL Algorithm can help you indeed. After the step two , we can write a few code to implement the function:
int main(){list<int> coll;//insert elements from 1 to 100for (int i=1; i<=100; ++i) {coll.push_back(i);}//search for prime numberlist<int>::iterator pos;pos = find_if (coll.begin(), coll.end(), //rangeisPrime); //predicateif (pos != coll.end()) {//foundcout << *pos << " is first prime number found" << endl;}else {//not foundcout << "no prime number found" << endl;}}]]>
There is a easy way to do it , the follow code isn't written by me but a classic method
E.G quote from STL tutorial reference
#include <iostream>#include <list>#include <algorithm>#include <cstdlib> //for abs()using namespace std;//predicate, which returns whether an integer is a prime numberbool isPrime (int number){//ignore negative signnumber = abs(number);// 0 and 1 are prime numbersif (number == 0 || number == 1) {return true;}//find divisor that divides without a remainderint divisor;for (divisor = number/2; number%divisor != 0; --divisor) {;}//if no divisor greater than 1 is found, it is a prime numberreturn divisor == 1;}]]>