POJ3978

/*
Description


A pretty straight forward task, calculate the number of primes between 2 integers. 


Given 2 integers A ≤ B < 105 what’s the number of primes in range from A to B inclusive. 


Note: A prime number is a positive integer greater than 1 and is divisible by 1 and itself only. For N to be prime it is enough to test the divisibility of numbers less than or equal to square root of N.
Input


As many as 1000 lines, each line contains 2 integers A and B separated by a space. Input is terminated when A = B = -1 (Do not process this line).
Output


For every line in input – except for the last line where A = B = -1 - print the number of prime numbers between A and B inclusive.
Sample Input


0 9999
1 5
-1 -1
Sample Output


1229
3
Source


Seventh ACM Egyptian National Programming Contest
*/
#include<iostream>
using namespace std;
bool isPrime(int n)//判断是否是素数
{
    if(n==1||n==0) return false;//1不是素数
    if(n!=2&&n%2==0) return false;//2是素数，清除2的倍数
    for(int i=3; i*i<=n; i=i+2)
    {
        if(n%i==0) return false;
    }
    return true;
}
int main()
{
    int a,b;
    int count;
    while(cin>>a>>b)
    {
        count=0;
        if(a==-1&&b==-1)
            break;
        for(int i=a; i<=b; i++)
        {
            if(isPrime(i)) count++;
        }
        cout<<count<<endl;
    }
    return 0;
}