[C--] for() if() loop[C--] for() if() loop
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Primes
Week 8, 2026
// week 8 challenge
#include
using namespace std;
bool isPrime(int n) {
if (n <= 1) return false;
for (int i = 2; i <= sqrt(n); i++)
{
if (n % i == 0) return false;
}
return true;
}
int main() {
int limit = 100000000;// 10000 x 10000
int plus = 0;
int minus = 0;
int keep, math, diff, square = 0;// difference markers
for (int i = 1; i * i <= limit; i++)
{
square = i * i;
math = i;
if (isPrime(square - 1))
{
diff = math - keep;
keep = square - 1;
math = square;
minus++;
std::cout << i << "^2 - 1 = " << square - 1 << "\n";
std::cout << "Difference: " << diff << "\n\n";
}
if (isPrime(square + 1))
{
diff = math - keep;
keep = i;
math = square;
plus++;
std::cout << i << "^2 + 1 = " << square + 1 << "\n";
std::cout << "Difference: " << diff << "\n\n";
}
}
std::cout << "--- Counts ---\n\n";
std::cout << "MinusOneCount: " << minus << "\n";
std::cout << "AddOneCount: " << plus << "\n";
return 0;
}
//EOF
