A counter thats faster than using an int and printf. It also never stops counting until 10^2^24, but you can increase the max int without slowing it down like with gmp.

counter.c

#include <stdio.h>
#include <stdlib.h>
int main(){char *d,*n=calloc(0x1000000,1);*n=48;for(;;){d=n;if(*d!=57)++*d;else{while(*d
==57)*(d++)=48;if(*d)++*d;else*d=49;}while(*++d);while(d--!=n)putchar(*d);putchar(13);}}

counterReadable.c

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

#define FLET '0' /* First Letter */
#define LLET '9' /* Last Letter */

int main()
{
  char* d;
  char* n = calloc(0x1000000,1);
  *n = '0';
  
  /* Loop */
  while(1)
  {
    /* Make Pointer To Begining */
    d = n;

    /* If first digit is not 9, stop */
    if(*d != LLET) { ++*d; }
    else
    {
      /* While the digit is 9, carry */
      while(*d == LLET) { *(d++) = FLET; }

      /* If you need to add a new digit */
      /* Then make room for a new digit */
      if(*d == '\0') { *d = FLET + 1; }
      else { ++*d; } /* Else just add 1 */
    }

    /* Print String Backwards*/
    while(*++d){} /* Get to the end of the string */
    /* Print string letter by letter backwards */
    while(d-- != n) { putchar(*d); }
    
    /* Return to the begining of the line */
    putchar('\r');
  }
}

counterWithBrackets.c

#include <stdio.h>
#include <stdlib.h>
int main(){char *d,*n=calloc(0x1000000,1);*n=48;for(;;){d=n;if(*d!=57){++*d;}else{while(*d==
57){*(d++)=48;}if(*d){++*d;}else{*d=49;}}while(*++d);while(d--!=n){putchar(*d);}putchar(13);}}