Inverse Polish method for solving mathematical expressions (c + +)

The main application of the stack, there are two functions deletespace (), stringtodouble () in my other blog: Some extension functions on string.

This procedure is only the basic function realization, does not have the error control.

#include <iostream> #include <stack> #include <string> #include <map> #include "fstring.h"/* * The inverse Polish representation is used to solve the mathematical expression * 1, the input infix representation is converted to a suffix expression * 2, the suffix expression is calculated to produce the result */using namespace std;stack<string> postorderstr;map <string, int> symbolpriority;void initializationsymbol (map<string, int>& symbol) {//define priority pair< String, int> element;element = Make_pair ("+", 0), Symbol.insert (element), element = Make_pair ("-", 0); Symbol.insert ( element = Make_pair ("*", 1), Symbol.insert (element), element = Make_pair ("/", 1); Symbol.insert (element);} void Strtopoststack (string& str, stack<string>& postorderstr) {//The input mathematical expression is first represented as a suffix expression stack<string > auxilary;//Auxiliary array for temporary storage of symbols string::iterator iter = Str.begin (); String::iterator iter1 = Iter;bool flag = false;// Whether to encounter parentheses for (; ITER! = Str.end (); ++iter) {if (*iter = = ' + ' | | *iter = = '-' | | *iter = ' * ' | | *iter = '/' | | *iter = '/' | | | *iter = = ') ' {if (iter1! = iter) {//may appear two consecutive symbols string subStr (Iter1, ITER);//Deposit Digital PostorDerstr.push (SUBSTR);} String symbol (iter,iter+1);//symbol is stored by priority, if (*iter = = ' (') {flag = True;auxilary.push (symbol);} else if (flag && *iter! = ') ') {Auxilary.push (symbol);} else if (!flag) {if (Auxilary.empty ()) {Auxilary.push (symbol);} Else{string TMP2 = Auxilary.top (); while (SYMBOLPRIORITY[TMP2] >= Symbolpriority[symbol]) {Postorderstr.push (TMP2); Auxilary.pop (); if (Auxilary.empty ()) BREAK;TMP2 = Auxilary.top ();} Auxilary.push (symbol);}} else if (flag && *iter = = ') ') {string tmp1 = Auxilary.top ();d O{postorderstr.push (TMP1); Auxilary.pop (); tmp1 = Auxi Lary.top ();} while (tmp1!= "("); Auxilary.pop (); flag = false;} Holds the next digit starting position iter1 = iter+1;}} String Tmp5 (Iter1, ITER);p Ostorderstr.push (TMP5), while (!auxilary.empty ()) {string tmp6 = Auxilary.top (); Postorderstr.push (TMP6); Auxilary.pop ();}} Double Computefun (stack<string> postorderstrnew) {//overflow control stack<double> computestack;//COMPUTE auxiliary stack while (! Postorderstrnew.empty ()) {string tmp7 = Postorderstrnew.top (); if (TMP7 = = "+" | | tmp7 = "-" || TMP7 = = "*" | | TMP7 = = "/") {//] The sign is taken out of the calculation auxiliary stack of two elements to start the calculation, and the results are pressed into the stack double value1, value2, value3;value1 = Computestack.top (); Computestack.pop (); value2 = Computestack.top (); Computestack.pop (); if (TMP7 = = "+") {Value3 = value2 + value1;} else if (TMP7 = = "-") {value3 = value2-value1;} else if (TMP7 = = "*") {value3 = value2 * value1;} Else{value3 = value2/value1;} Computestack.push (VALUE3);} Else{double value;//Converts the character to a value and presses it into the stack value = stringtodouble (TMP7); Computestack.push (value);} Postorderstrnew.pop ();} return Computestack.top ();} int main () {Initializationsymbol (symbolpriority); string mathstr;cout << "Please input a math string:" <<endl ; Getline (CIN,MATHSTR); cout << "The string you are input is:" << endl;deletespace (MATHSTR); cout << mathstr& Lt;<endl;strtopoststack (Mathstr, Postorderstr);stack<string> Postorderstrnew;while (!postOrderStr.empty ( ) {String tmp4 = Postorderstr.top ();//cout << tmp4 << "";//rollover to another stack is the suffix expression postorderstrnew.push (tmp4); PostorDerstr.pop ();} cout << endl;cout << "The compute result is:" <<computefun (postorderstrnew) <<endl;return 0;}

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Inverse Polish method for solving mathematical expressions (c + +)