Php-PHP source code

Php implements simple expression algorithm Php implements simple expression algorithm

Returns an expression.

$ Char = array (); // symbol stack $ number = array (); // number stack $ charnum = array ('+' => 1, '-' => 1, '*' => 2, '/' => 2 ); // specify the priority of the symbol stack $ arr = '4 + 2*5-7/11 '; // 4 2 5 * + 7 11/-inverse Polish expression $ arr = preg_replace ('/(\ s +)/', ', $ arr ); $ len = strlen ($ arr); $ flag = 0; $ j = 0; for ($ I = 0; $ I <$ len; $ I ++) {if (is_numeric ($ arr [$ I]) {if (! Isset ($ number [$ j]) $ number [$ j] = 0; if ($ flag = 1) $ number [$ j] = $ number [$ j] * 10 + $ arr [$ I]; if ($ flag! = 1) {$ number [$ j] = (int) $ arr [$ I] ;}$ flag = 1 ;}if (! Is_numeric ($ arr [$ I]) & is_string ($ arr [$ I]) {$ char [] = $ arr [$ I]; $ j ++; $ flag = 2 ;}} function do_operation ($ data1, $ data2, $ symbol) {switch ($ symbol) {case '+': return (double) ($ data1 + $ data2); case '-': return (double) ($ data1-$ data2); case '*': return (double) ($ data1 * $ data2); case '/': return (double) ($ data1/$ data2) ;}} function change_number (& $ arr, $ pos, $ temp) {$ I = $ pos; $ arr [$ I] = $ temp; $ I ++; $ len = count ($ arr)-1; while ($ I <$ len) {$ arr [$ I] = $ arr [$ I + 1]; $ I ++ ;} unset ($ arr [$ I]);} function change_char (& $ char, $ pos) {$ I = $ pos; $ len = count ($ char)-1; while ($ I <$ len) {$ char [$ I] = $ char [$ I + 1]; $ I ++ ;} unset ($ char [$ I]);} function char_value ($ char, $ charnum) {if (array_key_exists ($ char, $ charnum )) return $ charnum [$ char] ;}$ x1 =x2 x2 = 0; // Two pointers $ result = 0; $ lennum = count ($ number ); $ lenchar = count ($ char); while ($ x1 <$ lennum & $ x2 <$ lenchar) {// It is mainly calculated by symbols. Therefore, the priority of a symbol is very important. if (isset ($ char [$ x2]) & isset ($ char [$ x2 + 1]) & char_value ($ char [$ x2], $ charnum)> = char_value ($ char [$ x2 + 1], $ charnum) {if ($ result = 0) {$ result = do_operation ($ number [$ x1], $ number [$ x1 + 1], $ char [$ x2]); $ x1 ++; $ x2 ++;} else {$ result = do_operation ($ result, $ number [$ x1], $ char [$ x2]); $ x1 ++; $ x2 ++ }}// when only one symbol is left, else if ($ x2 = ($ lenchar-1) {$ result = do_operation ($ result, $ number [$ x1 + 1], $ char [$ x2]); break ;} else {// The symbol stack needs to remove a symbol and then move one digit to the other to change one digit to the other. $ temp = do_operation ($ number [$ x1 + 1], $ number [$ x1 + 2], $ char [$ x2 + 1]); change_number ($ number, $ x1 + 1, $ temp); change_char ($ char, $ x2 + 1); $ lennum = count ($ number); $ lenchar = count ($ char); var_dump ($ number); var_dump ($ char ); // if ($ x2 = 1) {echo $ lenchar; echo $ x1; exit ;}} echo $ result;

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