Question

Write a C function, for example void sumOfPrime(int n), that takes a positive int n as a parameter, put all prime numbers less than n into an array, and print out the array and the sum of the numbers in that array. You can use the isPrime function above to save time.

Answer 1

#include <stdio.h>

int isPrime(int num){
   int i;
   if (num <= 1) 
      return 0;
   if (num % 2 == 0 && num > 2) 
      return 0;
   for (i = 3; i < num / 2; i += 2){
      if (num % i == 0)
         return 0;
   }
   return 1;
}

void sumOfPrime(int n){
   int arr[1000];
   int k = 0, sum = 0, i;
   for(i = 2;i<n;i++){
      if(isPrime(i)){
         arr[k++] = i;
      }
   }  
   
   for(i = 0;i<k;i++){
      printf("%d ",arr[i]);
      sum += arr[i];
   }
   printf("\nSum = %d\n",sum);
}

int main()
{
   int n;
   printf("Enter value for n: ");
   scanf("%d",&n);
   sumOfPrime(n);
   return 0;
}

void sumOfPrime(int n){
   int arr[1000];
   int k = 0, sum = 0, i;
   for(i = 2;i<n;i++){
      if(isPrime(i)){
         arr[k++] = i;
      }
   }  
   
   for(i = 0;i<k;i++){
      printf("%d ",arr[i]);
      sum += arr[i];
   }
   printf("\nSum = %d\n",sum);
}