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

// check that chars from i to end are all digits 
bool digcheck_helper(char * str, int i) 
{ 
    if (str[i] == '\0') 
    { 
        // no more characters, so valid 
        return true; 
    } 
    else if (str[i] >= '0' && str[i] <= '9') 
    { 
        // str[i] is a digit, check rest recursively 
        return digcheck_helper(str, i + 1); 
    } 
    else 
    { 
        // str[i] is not a digit 
        return false; 
    } 
} 


//make sure all the characters are digits
//uses a helper function to get it started
bool digcheck(char * str) 
{ 
    return digcheck_helper(str, 0); 
}


int main()
{
   printf("hello world\n");

   char s[10] = "12333i";

   if (digcheck(s))
      printf("ok\n");
   else
      printf("not ok\n");

}