Question

How to find the sum of all the primes below two million in C

Answer 1

#include <math.h>
#include <stdio.h>
#include <stdbool.h>
  
bool isPrime(int n) {
    if (n == 0) return false;
    if (n == 1) return false;
  
    for (int i = 2; i <= sqrt(n); i++) {
        if (n % i == 0) {
            return false;
        }
    }
    return true;
}

int main(void) {
    long num = 2000000, sum = 0;
    
    for (int i = 2; i < num; i++) {
        if (isPrime(i)) {
            sum += i;
        }
    }
    
    printf("sum = %ld", sum);
}
  
  
  
  
/*
run:
  
sum = 142913828922
  
*/

 

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