Calculate the Infix Expression with Stack

This article summarizes the use of stacks (stack) to convert infix expressions (postfix expression) to postfix expressions (infix expression) and to calculate the results.

1 //calculation of string numbers (based on infix-to-suffix). cpp: The entry point that defines the console application. 2 //3 4#include"stdafx.h"5#include <string>6#include <stack>7#include <cctype>8#include <iostream>9 Ten //computes a suffix expression. (int type) One intPostfixexp (ConstSTD::string&exp) A { -std::stack<int>Numsta; -      for(inti =0; I! = Exp.size (); i++) the     { -         //to press a number in an expression into the stack -STD::stringnum; -          while(IsDigit (Exp[i])) +         { - Num.push_back (Exp[i]); +i++; A         } at  -         if(!num.empty ()) Numsta.push (Atoi (Num.c_str () )); -  -         //Encounter spaces continue iteration -         if(Exp[i] = =' ')Continue; -          in         //An operator pops up the top two elements of the stack and presses the result into the stack -         if(Exp[i] = ='+'|| Exp[i] = ='-'|| Exp[i] = ='*'|| Exp[i] = ='/') to         { +             intNUM1; -             intnum2; the             if(!numsta.empty ()) *             { $NUM1 =numsta.top ();Panax Notoginseng Numsta.pop (); -             } the             if(!numsta.empty ()) +             { Anum2 =numsta.top (); the Numsta.pop (); +             } -             //Calculation $             Switch(Exp[i]) $             { -              Case '+': Numsta.push (NUM1 +num2); -                  Break; the              Case '-': Numsta.push (NUM1-num2); -                  Break;Wuyi              Case '*': Numsta.push (NUM1 *num2); the                  Break; -              Case '/': Numsta.push (NUM1/num2); Wu                  Break; -             default: About                  Break; $             } -         } -  -     } A     returnnumsta.top (); + } the  - //infix suffix e.g. 2 + 3 * 5 + (7 * 8 + 9) * 2 3 5 * + 7 8 * 9 + * + $STD::stringPostfixtoinfix (ConstSTD::string&exp) the { theSTD::stringresult; thestd::stack<Char>operators; the      for(inti =0; I < exp.size (); i++) -     { in          while(IsDigit (Exp[i])) the         { the Result.push_back (Exp[i]); Abouti++; the         } the         //If the end number is non-single digit, the array index will be out of bounds, because string is not a true character array, the result is not affected by the cross-border the         //if (i >= exp.size ()) break; +         //Add a space separator -Result.push_back (' '); the         //Encounter spaces continue iterationBayi         if(Exp[i] = =' ')Continue; the         //when the operator is encountered, check the top element of the stack priority, if it is a high priority/equal priority operator, pop up the stack operator, after completion of the expression of the operator press into the         if(Exp[i] = ='+'|| Exp[i] = ='-') -         { -              while(!operators.empty () && operators.top ()! ='(') the             { the                 //when the top element of the stack is +-*/, (the lowest priority in the stack, the highest precedence in an expression ) the Result.push_back (Operators.top ()); the Operators.pop (); -Result.push_back (' '); the             } the Operators.push (Exp[i]); the         }94         Else if(Exp[i] = ='*'|| Exp[i] = ='/') the         { the              while(!operators.empty () && (operators.top () = ='*'|| Operators.top () = ='/')) the             {98                 //if (operators.top () = = ' * ' | | operators.top () = = '/') About Result.push_back (Operators.top ()); - Operators.pop ();101Result.push_back (' ');102             }103 Operators.push (Exp[i]);104         } the         Else if(Exp[i] = ='(') Operators.push ('(');106         Else if(Exp[i] = =')')107         {108              while(Operators.top ()! ='(')109             { the Result.push_back (Operators.top ());111 Operators.pop (); theResult.push_back (' ');113             } the             //Eject ( the Operators.pop (); the         }117         118     }119      while(!operators.empty ()) -     {121 Result.push_back (Operators.top ());122Result.push_back (' ');123 Operators.pop ();124     } the     126     returnresult;127 } - 129 intMain () the {131Std::cout << Postfixexp (Postfixtoinfix ("2 + 3 * 5 + (7 * 8 + 9) *")) <<Std::endl; theSystem"Pause");133     return 0;134}

Calculate the Infix Expression with Stack