Write a C program to find the sum of all prime numbers in an array?

Answer 1

Borrowing the isPrime function from another answer of mine. Note that this will result in terrible performance for large arrays of numbers. (You should look into one of the sieve algorithms for this)

// returns 1 if n is prime, 0 otherwise

void isPrime(const int n) {

// We know that if n is composite, then we will find a factor in the range [2,sqrt(n)]

// so we compute the square root only once to limit our number of calculations.

const int sqrt_n = sqrt(n);

// Iterate through possible factors

int i;

for( i = 2; i <= sqrt_n; ++i ) {

// If n is divisible by i (n%i==0) then we have a factor

if(!(n % i)) {

return 0;

}

}

// If we get here, we know n has no factors other than itself and 1

return 1;

}

// returns the sum of all prime numbers in nums

int findPrimeSum(const int numsLength, const int[] nums) {

int sum = 0;

// iterate through nums and add up all the primes

int i;

for(i = 0; i < numsLength; ++i) {

if( isPrime(nums[i] ) {

sum += nums[i];

}

}

return sum;

}