Hello I'm trying to create a program that reads a number(which is the amount of pairs) then you input the pairs and then for each pair it prints the prime numbers between the 2 numbers of the pair.Here's the code:

#include <iostream>
using namespace std;

class Prime {
int x,y;
public:
void count(int,int);
};

void Prime::count(int k,int l)
{
int f=k%2;
int g=k%3;
int h=k%5;
do
{
if  (f==0)
break;
else if (g==0)
break;
else if (h==0)
cout  <<  k;
k++;
} while (k<=l);
}
int main(void)
{
int * primes;
int n,i;
int a,b;
cout << "Give  the amount of numbers you wish to try:"<< endl;
cin  >> n;
primes = new int[n];
for (i=0;i<=(n-1);i++)
{
cout << "Give the 2 numbers:" << endl;
cin >> a >> b;
Prime primes[i];
primes[i].count(a,b);
}
}

break; on 19 and 21 is taking you out of the loop completely, what you want to do is increment k and continue; . Also, you employ something like http://en.wikipedia.org/wiki/Sieve_of_Eratosthenes because you're only testing for 3 factors.

Your primality tester is flawed, for example 49 according to this primitive test is prime (but for every number <49 it is correct). Also it will not finish if k>0, because only manipulation you do with k is incrementation in line 24, and in the following line you test it if it is less then 2.
PS. Good indention for Prime::count:

void Prime::count(int k,int l)
{
int f=k%2;
int g=k%3;
int h=k%5;
do
{
if  (f==0)
break;
else if (g==0)
break;
else if (h==0)
cout  <<  k;
k++;
} while (k<=l);
}
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