Can anybody see why the following piece of code does not provide the correct output for the calculation of the sum of all primes < 2 000 000?
Code:#include <stdio.h> #include <math.h> int isPrime(int numb) { int i, stop = 0; for (i = 2; !stop && i <= sqrt(numb); i++) { if (numb % i == 0) stop = 1; } if (!stop) return 1; else return 0; } int main() { int i, sum = 2; for (i = 3; i < 2000000; i += 2) { if (isPrime(i)) { printf("%i\n",i); sum += i; } } printf("%i\n", sum); return 0; }
What's the max value a signed integer type can store?
>What's the max value a signed integer type can store?
INT_MAX in limits.h
oh godthanks hahaha what a stupid mistake
A couple of issues:
1) isPrime doesn't handle 0 or 1 properly.
2) sqrt(numb) should really only be calculated once.
Oh, and just for fun...
Code:int sumOfPrimesUpTo(int numb) { int sum = (numb * (numb + 1)) / 2; for (int i = 0; i <= numb; ++i) if (!isPrime(i)) sum -= i; return sum; }
Code:#include <cmath> #include <complex> bool euler_flip(bool value) { return std::pow ( std::complex<float>(std::exp(1.0)), std::complex<float>(0, 1) * std::complex<float>(std::atan(1.0) *(1 << (value + 2))) ).real() < 0; }
