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Mcgee_00 on 10/11/08

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Last Edited at 10/11/08 07:16pm

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Infix notation to Reverse Polish Notation

/ Published in: C++

The bugged version: Somehow, it prints random characters to me like [] except the spaces filled in and other accented letters when I input more parenthesis and longer input.

How to use: example->
input:
3
1+2
(1+2)*(6-2)
6-7*(9*10)/8

output:
1 2 +
1 2 + 6 2 - *
6 7 - 9 10 ** 8 /

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#include <iostream>
#include <cctype>
#include <string>
#include <list>
#include <stack>

using namespace std;

char pop(list<char> & a)                 //Pops the stack and returns it, I use it to append to output vector
{
    char result = a.front();
    a.pop_front();
    return result;
}

int main()
{
    int num;
    string in;
    cin >> num;

string out;                                              //stores outputed characters front operator stack
    list<char> opr;
    for(int zed=0; zed<num; zed++) {
    cin >> in;

for(int i =0; i < in.length(); i++)
    {
        switch(in[i])                                         //Gets operator gets their precedence and pushes them into the stack(list) and
                                                              //output string
        {
            case '(': opr.push_front(in[i]);
                      break;
            case ')':  while(opr.front()!='(' && !opr.empty())
                       {
                          out.push_back(pop(opr));
                       }

opr.pop_front();
                      break;
            case '-': if(opr.front() == '+' || '*' || '^' || '/' || '%')
                      {
                          out.push_back(pop(opr));
                          opr.push_front(in[i]);
                      }
                      else opr.push_front(in[i]);
                      out.push_back(' ');
                      break;
            case '+': if(opr.front() == '-' || '*' || '^' || '/' || '%')
                      {
                          out.push_back(pop(opr));
                          opr.push_front(in[i]);
                      }
                      else opr.push_front(in[i]);
                      out.push_back(' ');
                      break;
            case '*': if(opr.front() == '^' || '/' || '%')
                      {
                          out.push_back(pop(opr));
                          opr.push_front(in[i]);
                      }
                      else opr.push_front(in[i]);
                      out.push_back(' ');
                      break;
            case '^': opr.push_front(in[i]);
                      out.push_back(' ');
                      break;
            case '/': if(opr.front() == '^' || '*' || '%')
                      {
                          out.push_back(pop(opr));
                          opr.push_front(in[i]);
                      }
                      else opr.push_front(in[i]);
                      out.push_back(' ');
                      break;
            default: if(isdigit(in[i]) || isalpha(in[i]))   //Default: if character is a digit or a letter append it to output
                out.push_back(in[i]);
        }

}

while(!opr.empty())                     //if the stack isn't empty push the rest into the output vector
        {
            out.push_back(pop(opr));
            opr.pop_front();
        }

out.erase(remove(out.begin(), out.end(),'('), out.end());  //remove those stupid parenthesis
    out.push_back('\n');
}

cout << out;

return 0;
}

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