C Exercises: Sum of all the multiples of 3 or 7 below 100

C Programming Challenges: Exercise-17 with Solution

The natural numbers below 10 that are multiples of 3 or 7 are 3, 7, 6 and 9. The sum of these multiples is 25.
Write a C programming to find the sum of all the multiples of 3 or 7 below 100.

C Code:

#include <stdio.h>
int main(void)
{
  int sum3 = 0, sum7 = 0, sum21 = 0;
  int i;
  for (i = 0; i < 100; i++) {
    if (i % 3 == 0) {
      sum3 += i;
    }
    if (i % 7 == 0) {
      sum7 += i;
    }
    if (i % 21 == 0) {
      sum21 += i;
    }
  }
  printf("%d\n", sum3 + sum7 - sum21);
  return 0;
}

Sample Output:

2208

Flowchart:

C Programming Code Editor:

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