Program C++ postfix infix

Berikut codingnya :

#include <iostream>
#include <sstream>
#include <stack>
#include <limits>
#include <string>
using namespace std;
int a(char p)
{
    int temp;
    if (p=='^')
        {
            temp=1;
        }
    else if (p=='*'||p=='/')
        {
            temp=2;
        }
    else if (p=='+'||p=='/-')
        {
            temp=3;
        }
    return temp;
}
int main()
{
    string infix;
    cout<<"Input infix? = ";
    getline(cin,infix);
    stack<char>opr_stack;
    stringstream postfix;
    for (unsigned i=0;i<infix.length();i++)
        {
            if (infix[i]=='+'||infix[i]=='-'||infix[i]=='*'||infix[i]=='/'||infix[i]=='^')
                {
                    while (!opr_stack.empty()&&a(opr_stack.top())<=a(infix[i]))
                        {
                            postfix<<opr_stack.top();
                            opr_stack.pop();
                        }
                        opr_stack.push(infix[i]);
                }
            else if (infix[i]=='(')
                        {
                            opr_stack.push(infix[i]);
                        }
            else if (infix[i]==')')
                        {
                            while (opr_stack.top()!='(')
                                    {
                                        postfix<<opr_stack.top();
                                        opr_stack.pop();
                                    }
                            opr_stack.pop();
                        }
            else
                {
                    postfix<<infix[i];
                }
        }
        while (!opr_stack.empty())
            {
                postfix<<opr_stack.top();
                opr_stack.pop();
            }
   cout<<"Postfix = "<<postfix.str()<<endl;
   cin.ignore(numeric_limits<streamsize>::max(),'\n');
    return 0;
}

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