Basic Algorithms personal PHP implementation (3)

<? PHP  /*  ** PHP strlen obtains the string length.  */  Function Getlength ( $ Str  ){  $ I = 0 ;  While ( $ Str [ $ I  ]) {  $ I ++ ;} Return   $ I  ;}  //  Echo getlength ('123456789a ');  /*  ** PHP strrev string flip  */   Function Str_rev ( $ Str  ){  If ( $ Str <= 1) Return  ;  $ Res_str ='' ;  For ( $ I = Strlen ( $ Str ); $ I > = 0; $ I -- ){  $ Res_str . = $ Str [ $ I  ];}  Return   $ Res_str ;}  //  Echo str_rev ('1234aabbccc ');   /*  ** PHP strstr search string $ I + $ len2 <= $ len1  */    Function Str_str ( $ Str , $ Sub_str  ){  $ Len1 = Strlen ( $ Str  );  $ Len2 =Strlen ( $ Sub_str  );  If ( $ Len1 < $ Len2 ) Return 'Invalidarguments' ;  For ( $ I = 0; $ I <= $ Len1 - $ Len2 ; $ I ++ ){//  Someone on the Internet judges that $ I <= ($ len1-$ len2) + 1 is puzzled.            If ( Substr ( $ Str , $ I , $ Len2 ) = $ Sub_str  ){  Return   Substr ( $ Str , $ I  );}} Return 'Can \'t find' ;}  Echo Str_str ('Hello world', 'D' ); ?>