How do I filter the output so that only filenames are displayed and not folders?

Question

#include <dirent.h> 
#include <stdio.h> 

int main(void) {
  DIR *d;
  struct dirent *dir;
  d = opendir(".");
  if (d) {
    while ((dir = readdir(d)) != NULL) {
      printf("%s\n", dir->d_name);
    }
    closedir(d);
  }
  return(0);
}

I have a working piece of code here. This program prints file and folder names in a given directory together. How can i do some filter operation to show only file names?