project euler problem 10:Summation of primes

题意：二百万以下的素数相加

#include <iostream>#include <map>#include <string>#include <cstring>#include <cstdio>#include <cmath>#include <algorithm>using namespace std;bool a[2000005];void abc(){    int i,j;    a[1]=true;    for(i=2;i<=2000005;i++)        if(!a[i])        {            for(j=2*i;j<=2000005;j+=i)                a[j]=true;        }}int main(){    long long i,sum=0;    abc();    for(i=1;i<=2000000;i++)    {        if(!a[i]) sum+=i;    }    cout<<sum<<endl;    return 0;}