Prime numbers

[Beginner1551]

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

 #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;
}

[cire]

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? ;)

[Beginner1551]

I know that loop keeps executing even though I don't need it to anymore, I just don't know how to stop it.