Factors and Prime Numbers

[OrDidHe]

I'm trying to write a program that will find all the factors and primes for a range of numbers. I have the inner loop working but I am having trouble writing the outer loop that will output the range of numbers instead of just finding the factors for one number. Any help would be appreciated.

    int n1 = 0;
    int n2;
	int factor = 0;
	cout << "Enter a starting number: ";
	cin >> n1;
	cout << "Enter a ending number: ";
	cin >> n2;
    cout << "Finding factors and primes between " << n1 
         << " and " << n2 << endl;
    cout << "The factors of " << n1 << " are: [";

    for(int i = 2; i < n1 ; i++)
    {
	if(n1 % i == 0)
	{
	cout << i << " ";
			factor++;
	}
    }
    cout << "]";
    if(factor == 0)
    {
    cout << " Number is prime!" << endl;
    }
 return 0;
}

[OrDidHe]

So if the user inputs 2 for the starting number and 6 for the ending number the output would look like this:

The factors of 2 are: [] It is prime!
The factors of 3 are: [] It is prime!
The factors of 4 are: [2 ] 
The factors of 5 are: [] It is prime!
The factors of 6 are: [2 3 ]

[TheKingOfTyrants]

Would you just want to do something like this? Loop through the range the user provides?

for (int current = n1; current <= n2; ++current)
{
    //include loop you've already written, replacing every instance n1 with the variable current
}

[Java90]

hi:

The factors of both number?? or factors of each number between both numbers???

I going to help you with the primes:

int n1 = 0; I don't know why if you going to ask after a number n1. put just

int n1;

the loops:

for(int i=n1 ; i<=n2 ; i++)
    {
        int factor = 0;

        for(int j=1 ; j<=i ; j++)
        {
            if(i%j == 0)
            {
                factor++;
            }
        }
        if(factor == 2)
        {
            cout<<i<<" ";
        }
    }
    cout<<"]"<<endl;

    cin.get();
    return 0;

This show you the prime numbers in the range.

[OrDidHe]

Right now my code will output just the beginning number factors. So if six is the beginning number the output will be:

FACTORS AND PRIMES PROGRAM
Finding factors and primes between
This program will find factors and primes.
Enter a starting number: 6
Enter a ending number: 6
Finding factors and primes between 6 and 6
The factors of 6 are: [2 3 ]

I'm trying to write a loop that will print the factors from the beginning number to the ending number. So if the inputs are 2,6 it will output the following:

FACTORS AND PRIMES PROGRAM
Finding factors and primes between
This program will find factors and primes.
Enter a starting number: 2
Enter a ending number: 6
Finding factors and primes between 2 and 6
The factors of 2 are: [] It is prime!
The factors of 3 are: [] It is prime!
The factors of 4 are: [2 ] 
The factors of 5 are: [] It is prime!
The factors of 6 are: [2 3 ]

[OrDidHe]

So I think I have figured out the outer loop part. However, now I am running into an issue with the primes. For some reason it will not continue to print "It is prime!"

Here's how the code is written now:

#include <iostream>


using namespace std;
int main()
{
	//Heading
	cout << "FACTORS AND PRIMES PROGRAM" << endl;
    	cout << "Finding factors and primes between" << endl;
    	cout << "This program will find factors and primes." << endl;

	//Request inputs
    	int n1;
    	int n2;
	int factor = 0;
	cout << "Enter a starting number: ";
	cin >> n1;
	cout << "Enter a ending number: ";
	cin >> n2;
    	cout << "Finding factors and primes between " << n1 << " and " << n2 << endl;
	
	//Outer Loop
    	int n;
    	n = n1;
	while (n <= n2)
	{
	   cout <<    "The factors of " << n << " are: [";
	   
	   //Inner Loop
    	   for(int i = 2; i < n ; i++)
	   {
	   
	        //Factor Output
		if(n % i == 0)
		{
		cout << i << " ";
		factor++;
		}
       	   }
    	        cout << "]";

		//Prime Output
    		if (factor == 0)
		{
	        cout << " It is prime!";
	        }

                cout << "\n";
	        n++;
	   }
return 0;
}

If the input is 2, 6 it will output the following without stating 5 "is prime" :

FACTORS AND PRIMES PROGRAM
Finding factors and primes between
This program will find factors and primes.
Enter a starting number: 2
Enter a ending number: 6
Finding factors and primes between 2 and 6
The factors of 2 are: [] It is prime!
The factors of 3 are: [] It is prime!
The factors of 4 are: [2 ] 
The factors of 5 are: []
The factors of 6 are: [2 3 ]

[OrDidHe]

Looks like I just had to change the prime if statement to:

if ((n % 2 != 0) || (n / 2 ==1))
{
   cout << " It is prime!";
}

[48T7M4Gy]

http://www.cplusplus.com/forum/beginner/144496/