#include <stdio.h>

int entab(char s[], int lim, int col) {
  int c, i, t;
  for (i=0,t=0; i < lim-1 && (c=getchar())!=EOF && c!='\n';i++,t++) {
    /*
    * c is the character representation as integer
    * i is the current column on the copied string
    * t is the current column on the original string
    *
    * t is used to count tab stops because i goes back when spaces are replaced by tabs.
    * i and t are both modified, however only i changes in contexts other than the routinal increase.
    * c is set to i's position and t is only used in tab stop counting
    */
    if (t >= col && t%col == 0 && s[i-1] == ' ' && s[i-2] == ' ') {
      int x;
      for (x = i; s[x-1] == ' ' && i-col < x; x--);
      s[x] = '\t';
      i = ++x;
    }
    s[i] = c;
  }
  if (c == '\n')
    /*
    * If it is the end of the string, represented by a new line,
    * add that new line and increase it for the \0 addition
    */ {
    s[i] = c;
  }
  /*Add the string end and return it to the previous context*/
  if (lim-1 > i) {
    s[i+1] = '\0';
  } else {
    s[lim-1] = '\0';
  }
  return i;
}