c - Pointer Arithmetics and Char array -

i having trouble understanding following code. although tried debug time seems can't understand exact mechanics of code , feeling stuck. appreciated.

edit: problem located on recursive function , how know when stop calling self.

int main(){   char word[10]="abcdfb";   dosomethingelse(word);   printf("%s",word);   return 0; }  void dosomethingelse(char * w){   static char * s =null;   char t;   if(!s){     s=w;   }   if(*w==0)return;   dosomethingelse(w+1);   if(s>w)return;   if(*w -*s==1){     t=*s;     *s=*w;     *w=t;   }    s++;   return; } 

the recursive function calls stop after dosomethingelse(w+1) gets "bcdfb", "cdfb", "dfb", "fb", "b", "" -> if(w[0] == '\0') return. places execution stack of function calls each char, going backwards. static variable s goes forward. after cleaning-up, more clear happens:

#include <stdio.h> /* printf */ #include <string.h> /* strlen */  /* prototype */ void swapconsectutiveletters(char * word);  /** provides word. */ int main(void) {     char word[10] = "abcdfb";     swapconsectutiveletters(word);     printf("%s", word);     return 0; }  /** detects consecutive letters occurring in n-th first,  last , swaps them. */ void swapconsectutiveletters(char * word) {     char * end;     /* nothing: null, empty, or 1-char string. */     if(!word || word[0] == '\0' || word[1] == '\0') return;     /* obtain pointer end of string. */     end = word + strlen(word) - 1;     /* swaps consecutive letters. */     {         if(end[0] - word[0] == 1) {             char temp = word[0];             word[0]   = end[0];             end[0]    = temp;         }     } while(++word < --end); }