Project Euler, Problem #12, C

/* The sequence of triangle numbers is generated by adding the natural
 * numbers. So the 7th triangle number would be
 * 1 + 2 + 3 + 4 + 5 + 6 + 7 = 28. The first ten terms would be: 1, 3,
 * 6, 10, 15, 21, 28, 36, 45, 55, ... Let us list the factors of the
 * first seven triangle numbers: 1: 1; 3: 1, 3; 6: 1, 2, 3, 6; 10:
 * 1, 2, 5, 10; 15: 1, 3, 5, 15; 21: 1, 3, 7, 21; 28:
 * 1, 2, 4, 7, 14, 28 We can see that 28 is the first triangle number
 * to have over five divisors. What is the value of the first triangle
 * number to have over five hundred divisors? */

#include <stdio.h>
#include <math.h>

int main()
{
     /* counter */
     int cntr = 2;
     /* current triangle number */
     int ctn = 1;
     /* divisions number */
     int dn = 0;
     /* maximum divisor */
     int md;
     /* divisor */
     int d;

     while(1)
     {
          ctn = ctn + cntr;
          md = (int)sqrt((double)ctn);

          if(ctn % 2 == 0)
          {
               for(d = 1; d <= md; d++)
                    if(ctn % d == 0)
                         dn += 2;
          }
          else
          {
               for(d = 1; d <= md; d += 2)
                    if(ctn % d == 0)
                         dn += 2;
          }

          if(md == (int)ceil(sqrt((double)ctn)))
               dn--;

          if(dn > 500)
               break;

          dn = 0;
          cntr++;
     }
     printf("%d\n", ctn);
     return(0);
}

/* 76576500
 *
 * real 0m0,368s
 * user 0m0,368s
 * sys  0m0,000s */