筛选素数个数（10^8以内）

int sushu(int m){char *is=new char[m+1];memset(is,0,sizeof(char)*(m+1));int i,j,k=1;for(i=3;i<=m;i+=2){for(j=3;j<=i,j*i<=m;j+=2){is[i*j]=1;}if(is[i]==0)k++;}delete is;return k;}int main(){int m,n;while(scanf("%d",&m),m){if(m<2){puts("0");continue;}printf("%d\n",sushu(m));}return 0;}