data_structures/infixToPostfix.cpp at master · Keshav002/data_structures · GitHub

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#include<iostream>
#include<stack>

using namespace std;

//This function will return precedence of operators
int prec(char c)
{
    if(c == '^')
    return 3;
    else if(c == '*' || c == '/')
    return 2;
    else if(c == '+' || c == '-')
    return 1;
    else
    return -1;
}

void infixToPostfix(string s)
{
    stack<char> st;
    st.push('N');
    int l = s.length();
    string s2;
    for(int i = 0; i < l; i++)
    {
        if((s[i] >= 'a' && s[i] <= 'z')||(s[i] >= 'A' && s[i] <= 'Z'))
        s2+=s[i];

        else if(s[i] == '(')

        st.push('(');

        else if(s[i] == ')')
        {
            while(st.top() != 'N' && st.top() != '(')
            {
                char c = st.top();
                st.pop();
               s2 += c;
            }
            if(st.top() == '(')
            {
                char c = st.top();
                st.pop();
            }
        }

        else{
            while(st.top() != 'N' && prec(s[i]) <= prec(st.top()))
            {
                char c = st.top();
                st.pop();
                s2 += c;
            }
            st.push(s[i]);
        }

    }
    while(st.top() != 'N')
    {
        char c = st.top();
        st.pop();
        s2 += c;
    }

    cout << s2 << endl;

}

// Function for merging two stacks

void Merge(stack<int>& s1, stack<int>& s2)
{

    stack<int> mergedStack;
    while (!s1.empty()) {
        mergedStack.push(s1.top());
        s1.pop();
    }
    while (!s2.empty()) {
        mergedStack.push(s2.top());
        s2.pop();
    }

     while (!mergedStack.empty()) {
        cout << mergedStack.top() << " ";
        mergedStack.pop();

    }
}

  void input(stack<int>& s){
      int n, val;
      cin>>n;
      for(int i=0;i<n;i++){
          cout<<"Enter value" <<i+1<<" : ";
          cin>>val;
        s.push(val);

      }

  }


int main()
{
    // cout<<"Enter 1 for infix to postfix conversion : \n";
    // cout<<"Enter 2 for merging two stacks : ";
    // int x;
    // cin>>x;
    // if(x == 1){
        cout<<"Enter the infix expression : ";
    string exp;
    cin>>exp;
    infixToPostfix(exp);

    // }
    // if(x == 2){
    //     stack<int> s1;
    //     stack<int> s2;
    //  cout<<"Enter the no of elements in First stack : ";
    //   input(s1);
    //  cout<<"Enter the no of elements in Second stack : ";
    //   input(s2);
    //      cout<<"Merged Stack : ";
    //   Merge(s1, s2);
    // }


    return 0;
}