Prime numbers

Why does my code print so many of the same prime number?

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
 #include <iostream>
#include <cstdlib>
#include <fstream>

using namespace std;

int main()
{		
	int num;	
										
	cout << endl << "Please enter an integer larger than 50: ";
	cin >> num;
	cout << endl; 
	
	while (num <= 50)		
	{						
		cout << "You have entered a value less than 50. ";
		cout << "Please enter a valid value: ";
		cin >> num;
	}
	
	int a[20];
	ofstream outfile;					
	outfile.open("Random.txt");			
	
	for(int i = 0; i < 20; i++)			
	{											
		outfile << rand()%(num) + 1 << endl;	
	}
	
	outfile.close();					
	
	ifstream infile;					
	infile.open("Random.txt");			
	
	while(infile >> num)				
	{
		//if(num == 1)							
		
		for(int i = 2; i < num - 1; ++i)		
		{
			if(num % i == 0)					
			{
				//nothing
			}
			
			else if (num % i != 0)
			{
				cout << num << endl;
			}
		}
				
	}

	infile.close();		
	return 0;
}
Removing some of your code to make things simpler to test:

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
#include <iostream>
#include <cstdlib>
#include <fstream>
#include <sstream>

using namespace std;

std::istringstream in("4 6 8");

int main()
{
    unsigned num;
    while (in >> num)
    {
        std::cout << "Processing " << num << '\n';
        //if(num == 1)							

        for (unsigned i = 2; i < num - 1; ++i)
        {
            if (num % i == 0)
            {
                //nothing
            }

            else if (num % i != 0)
            {
                cout << num << endl;
            }
        }

        std::cout << "Done processing " << num << '\n';
    }
}
Processing 4
Done processing 4
Processing 6
6
Done processing 6
Processing 8
8
8
8
Done processing 8


What does your code have to do with primes? ;)
I know that loop keeps executing even though I don't need it to anymore, I just don't know how to stop it.
Topic archived. No new replies allowed.