Someone

char* concatenaCadenas(char* carac1, const char* carac2) {
      int=-1, j=0;
      while (carac1[++i]j='\0')
      ;
      while (carac2[j]!='\0')
      carac1[i++]=carac2[j++];
      carac1[i]='\0';
      return carac1;
      }