아래 예제가 도움이 되실 지도 모르겠습니다.

#include <string.h>

#include <stdio.h>

//function for printing result
void print_result(int res[], int size, char isTen) {
  int len;
  if (isTen)
    len = size / sizeof(int);
  else
    len = (size / sizeof(int)) - 1;
  for (int i = 0; i < len; i++)
    printf("%d ", res[i]);
  printf("\n");
}

int main(int argc, char * argv[]) {
  char str[] = "139";
  int len = strlen(str);

  //initialize array (with lenght + 1 to avoid recreating array in case input is 99, 999 etc.)
  int res[len + 1];
  for (int i = 0; i < len; i++) {
    res[i] = (int) str[i] - '0';
  }

  //adding 1 to last element
  res[len - 1]++;

  //looping from last element to first
  int i = len;
  while (i > 0) {
    if (res[i] == 10) {
      res[i] = 0;
      res[i - 1]++;
    }
    i--;
  }

  //fixing 99, 999 etc. (with isTen boolean)
  char isTen = 0;
  if (res[0] == 10) {
    res[0] = 1;
    for (int i = 1; i < (len + 1); i++)
      res[i] = 0;
    isTen = 1;
  }

  //printing result
  print_result(res, sizeof(res), isTen);

  return 0;
}