Prime numbers program

Question

I\'m currently trying out some questions just to practice my programming skills. ( Not taking it in school or anything yet, self taught ) I came across this problem which re

Answer 1

Here is my code. When working on a big number, it's very slow! It can calculate all prime numbers with in the number you input!

#include 
#include 
#include 
using namespace std;

int main()
{
    int m;
    int n=0;
    char ch;
    fstream fp;
    cout<<"What prime numbers do you want get within?  ";
    if((cin>>m)==0)
    {
                 cout<<"Bad input! Please try again!\n";
                 return 1;
    }
    if(m<2)
    {
        cout<<"There are no prime numbers within "<(sqrt(i))+1;
            fp.seekg(0,ios::beg);
            fp>>j;
            for(;j>j)==NULL)
                    {
                        j=3;
                    }
                }
            }
            if(j>=sq)
            {
                fp.seekg(0,ios::end);
                fp<