CODEWITHSUNDEEP
c++stack
bradym55
bradym55

Reputation: 83

C++ Stack; Remove top value and placing into variable

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

using namespace std;

void interpretExpressionFile(string filepath)
{

    // Declare a stack of ints
    stack<int>myStack;

    while (true)
    {
        char ch;
        fin >> ch;

        if (fin.eof())
        {
            break;
        }

        if (isspace(ch))
        {
            continue;
        }

        if (isdigit(ch))
        {
            int value = (ch - '0');

            // Push value onto the stack:
            myStack.push(value);
        }
        else
        {

My problem is here beneath these two TODOs. I know what I need to do at this point, but I am having trouble as the program continues to output -1.

        // TODO: Remove top value from the stack placing it into value2
            myStack.pop();
            int value2 = -1;

            // TODO: Remove top value from the stack placing it into value2
            myStack.pop();
            int value1 = -1;

            int result;
            switch (ch)
            {
                case '+':  result = value1 + value2;  break;
                case '-':  result = value1 - value2;  break;
                case '*':  result = value1 * value2;  break;
                case '/':  result = value1 / value2;  break;
                default:  cout << "Unexpected operator: " << ch << endl;  return;
            }

            // TODO: Push the value in variable result back onto the stack:
            myStack.push(result);
        }
    }

    fin.close();

My other problem lies here. This is where I think I am getting messed up as well.

    // TODO: pop the top value off of the stack placing it into varresult:
    myStack.pop();
    int result = -1;
    cout << filepath << " - result is: " << result << endl;
}

int main()
{
    interpretExpressionFile("expression1.txt");
    interpretExpressionFile("expression2.txt");
    interpretExpressionFile("expression3.txt");
}

Upvotes: 1

Views: 1391

Answers (1)

GigaRohan
GigaRohan

Reputation: 747

If you want get the value at the top of the stack, then use stack::top(), not stack::pop() and then call pop() afterwards to remove the top element from the stack. So, you'd do:

int result2 = myStack.top();
myStack.pop();

Upvotes: 4

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