# Project Euler Problem 7

December 15, 2011

I mentioned yesterday, I’ve been doing the first few problems of Project Euler and figured I’d share my solution to problem 7 here.

The Problem
By listing the first six prime numbers: 2, 3, 5, 7, 11, and 13, we can see that the 6th prime is 13.
What is the 10,001st prime number?

The Solution
Let’s define a function isPrime(num) (granted, could be more efficient) and loop through the natural numbers, counting those that are prime.

```/**
* Find the difference between the sum of the squares of the first one hundred natural numbers and the square of the sum.
**/
#include
using namespace std;

bool isPrime ( unsigned long num ) {
for(int i = num - 1; i > 1; i--) {
if(num % i == 0) {
return false;
}
}
return true;
}

int main () {
unsigned long num = 2, primeCount = 0;

while ( primeCount < 10001 ) {
if ( isPrime (num) ) {
primeCount++;
cout << "Prime " << primeCount << " " << num << " is prime" << endl;
}
num++;
}

return(0);
}```

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