#include <stdio.h>
  void reverse(char * str){
           char * end = str;
           char tmp;
           if(str){
               while(*end){
                   ++end;
               }
              --end;
              while(str<end){
                  tmp = *str;
                  *str++ = *end;
                  *end-- = tmp;
              }
          }
  }
  int main(){
      char str[] = "abcd";
      reverse(str);
      printf("%s\n",str);
  }
 

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