Answer L15

#include <stdio.h>
#include <stdlib.h>

/* Puzzle L15 -- For each integer N from 1 to 25 compute
|                and print the sum 1+2+...+N
|
*/
int main()
{
  int N = 25;   /* line number */
  int sum=0;     /* Sum */
  int j;         /* values 1..25 to add to the sum */

  printf( "N \t Sum\n");
  for (j=1; j<=N; j++)
  {
    sum += j;
    printf("%d \t %d\n", j, sum );
  }
  
  
  return 0;
}

The not-smart way to do this is to computed each sum individually in a loop for each value of j.