Program to Test Large Number for Prime

[UofFprogrammer]

For a fun challenge, I am trying to create a C++ program that will determine if a number is prime. I am getting to problems when I reach a large values (over 9 or so digits).
How can I increase the number of digits i can use?
For example, when i use the number 4362206209 (which I know for a fact is prime) it returns 2 as a factor, which it isn't.
Eventually, I would like to get to long (50+ digit) numbers. I know this calculation would take a long time, but i have several (mathematical) tricks for cutting down on the numbers tried... if I could only get the computer do divide it for me.

Here's my code for the simplist program:

#include<iostream>
#include<cmath>
 
using namespace std;
int main (){
    unsigned long int primeNumber, testNumber =1, testResult = 1;
    cin>>primeNumber;
    bool prime=false;
    while (!prime & testNumber <= sqrt(primeNumber)){
        testNumber++;
        testResult = primeNumber % testNumber;
        if (testResult == 0){
            prime = true;
        }
    }
    if(prime){
        cout<<"first factor is : "<<testNumber;
    }
    else{
        cout<<"it's a prime number";
    }
    return 0;
}
 

Thank you

[Ganon11]

Your large numbers are not working properly because they are larger than what an unsigned long can hold (its max value is 4,294,967,296). In order to alleviate this, you could possibly evaluate these numbers by their binary equivalent using a bitset? Maybe? I have never actually used this, so I'm not sure how well it will work.

[RRick]

A long int is the same size as an int on many systems. In this case, your have run into a number greater than the 32 bit integer resolution on your system.

Try using unsigned long long int instead. On some systems this will create 64 bit integers, which is good for integers up to 18446744073709551616ULL.

[UofFprogrammer]

Thanks, but is there a way I can put very large numbers in? I can put a lage (50+ digit) number into an array, but I'm not sure how i could handle division in this case.
I am particularly interested in the RSA- Factoring Challenge where the numbers can be as long as 600+ digits.

http://en.wikipedia.org/wiki/RSA_Factoring_Challenge
Any advice?

I tried the unsigned long long int and that worked, but I wanted to use larger numbers.
Thanks

[weaknessforcats]

I tried the unsigned long long int and that worked, but I wanted to use larger numbers.
Thanks

You will need to use arrays probably as a struct member and various functions for math operations on the arrays.

[UofFprogrammer]

You will need to use arrays probably as a struct member and various functions for math operations on the arrays.

Could you perhaps provide a (simple) example to help me get started?

Thank you

[weaknessforcats]

You write a class that contains a string.

There should be member for the sign.

There should be a member for the location of the decmimal point.

To Add, you position to the least signifcant character and add the values. If greater than 9, you have a carry, etc.. You will work this out like you were doing it on paper. Most likely this will be the operator+ method.

I shouldn't be too hard.