Expression:Deque iterator not dereferencable

Question

I am writing program in C++ to convert infix to postfix. Here is my code.

#include<iostream>
#include<stack>
#include<string.h>

using namespace std;


int getPrecedence( char tmp )
{
    if(tmp=='+')
    {
        return 1;
    }
    else if(tmp == '-')
    {
        return 1;
    }
    else if(tmp == '*')
    {
        return 2;
    }
    else if(tmp == '/')
    {
        return 2;
    }
}

int main()
{

    stack<char> st;

    char expression[10];


    //cout<<"Enter expression : ";
    //cin>>expression;

    strcpy(expression,"a+b*c/d-e");

    char postfix[100];  // its postfix string
    int counter=0;

    int i=0;


    while( expression[i] != '\0' )  // iterate till '/0' does not come.
    {
        if(expression[i]== '+' || expression[i]== '-' || expression[i]== '*' || expression[i]== '/'  )
        {
            if( st.empty() )
            {
                st.push(expression[i]);
            }
            else // when stack not empty
            {
                int topPrecedence = getPrecedence( st.top() );
                int expressionPrecedence = getPrecedence( expression[i] );


                while( !(topPrecedence < expressionPrecedence) )
                {
                    postfix[counter++] = st.top();
                    st.pop();
                    topPrecedence = getPrecedence( st.top() );
                }

                if( st.empty() )
                {
                    st.push( expression[i] );
                }

                if( topPrecedence < expressionPrecedence )
                {
                    st.push( expression[i] );
                }


            }
        }
        else // when its an alphabet 
        {
            postfix[counter++] = expression[i];
        }


        i++;
    } // outer while ends 

    while( ! st.empty() )
    {
        postfix[counter++] = st.top();
        st.pop();
    }


    postfix[counter] = '\0';
    i=0;

    while( postfix[i] != '\0' )
    {
        cout<<postfix[i]<<" ";
        i++;
    }



    system("pause");
    return 0;
}

For example if input expression is a+b*c/d-e. Till d it converts expression postfix. But when - comes. It shows following error.

Expression:deque iterator not dereferencable

Apparently its related to Queue and I have not even used Queue.

Screen capture: https://www.facebook.com/photo.php?fbid=241461649373492&set=a.118955391624119.1073741827.100005289761090&type=1

Answer 1

The stack is a container adaptor.

By default it adapts a deque. You're probably just popping from an empty stack.