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stacks

This is a discussion on stacks within the C++ Programming forums, part of the General Programming Boards category; Hello, I'm trying to do this stack container that reads a string and is supposed to find if the string ...

  1. #1
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    stacks

    Hello,

    I'm trying to do this stack container that reads a string and is supposed to find if the string has a balanced parentheses (opening and closing parentheses). for example

    Z+ X- Y //no parentheses
    Z * X / (Y+10) //Matching parenthesis
    Z * ((X / Y) + D + (F-10) //Parenthesis donít match. Missing right parenthesis
    Z * (X / Y) + W + (F-10)) //Parenthesis donít match. Missing left parenthesis

    so far this is what I got

    Code:
    #define STACK_MAX 100
    
    class Stack {
    
        private:
            int        data[STACK_MAX];
            int        size;
    
        public:
            Stack() {       // Constructor
                size = 0;
            }
    
            ~Stack() { }    // Destructor
    
            int top() {
    
                if (size == 0) {
                    printf("Error: stack empty\n");
                    return -1;
                }
                return data[size-1];
            }
    
            void push(int d) {
    
                if (size < STACK_MAX)
                    data[size++] = d;
                else
                    printf("Error: stack full\n");
            }
    
            void pop() {
    
                if (size == 0)
                    printf("Error: stack empty\n");
                else
                    size--;
            }
    };
    
    int
     main()
    {
      
    
    
      return 0;
    }

  2. #2
    Registered User manasij7479's Avatar
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    The stack looks okay.
    The problem in question doesn't really require a stack though..
    All you have to do is to read the expression character by character.
    When you find a '(' increment a counter, and ')' to decrement.
    The final count determines the result. ( 0 depicting no error).
    Manasij Mukherjee | gcc-4.8.2 @Arch Linux
    Slow and Steady wins the race... if and only if :
    1.None of the other participants are fast and steady.
    2.The fast and unsteady suddenly falls asleep while running !



  3. #3
    Algorithm Dissector iMalc's Avatar
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    Please delete the empty non-virtual destructor. It has become annoyingly common for people to think they need to add that when in fact they don't.

    Your next steps would appear to be reading in the string, and then processing it, possibly making use of yout stack. You don't actually need a stack for this task as it is written, but presumably you need to be doing slightly more than you've told us.
    So what's the problem?
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  4. #4
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    This is where I am right now. I think this should work, but it's not doing what's supposed to do.

    Code:
    // A simple Integer stack, Array based
    #include <algorithm>
    #include <cassert>
    #include <iostream>
    #include <cstdlib>
    #include <string>
    
    using namespace std;
    
    #define STACK_MAX 100
    
    class Stack {
    
        private:
            int        data[STACK_MAX];
            int        size;
    
        public:
            Stack() {       // Constructor
                size = 0;
            }
    
            ~Stack() { }    // Destructor
    
            int top() {
    
                if (size == 0) {
                   cout << "Error: stack empty\n";
                    return -1;
                }
                return data[size-1];
            }
    
            void push(int d) {
    
                if (size < STACK_MAX)
                    data[size++] = d;
                else
                    cout << "Error: stack full\n";
            }
    
            void pop() {
    
                if (size == 0)
                    cout << "Error: stack empty\n";
                else
                    size--;
            }
    
            bool isEmpty() {
                if (size == 0)
                    return -1;
                        else
                            return 1;
            }
    };
    
    int main()
    {
    const char left_p = '(';
    const char right_p = ')';
    bool error = false;
    char ch;
    
    Stack s;
    
    cout << "Please enter an algebraic expression: ";
    cin.get(ch);
    
    	while (( ch != '\n')  && (!error) )
        {
    		if (ch == left_p)
    			 s.push(ch);
    
    
    		if (ch == right_p)
    			//if (s.isEmpty())
                 //   error = true;
                  //  else
                        s.pop();
                        cin.get(ch);
    	}
    		if ((!error) && s.isEmpty())
    		cout<<"\nResult: This expression is valid. \n"<<endl;
                else
                    cout<<"\nResult: This expression is invalid. \n"<<endl;
      return 0;
    }

  5. #5
    Programming Wraith GReaper's Avatar
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    Quote Originally Posted by manasij7479 View Post
    When you find a '(' increment a counter, and ')' to decrement.
    The final count determines the result. ( 0 depicting no error).
    Just want to add that the counter should be decremented only when it's larger than zero, to avoid situations like the following being interpreted as correct:
    X * ) Y + Z (
    manasij7479 likes this.
    Devoted my life to programming...

  6. #6
    Algorithm Dissector iMalc's Avatar
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    Please give an example input, the output you are getting, and for good measure also state the expected output.
    My homepage
    Advice: Take only as directed - If symptoms persist, please see your debugger

    Linus Torvalds: "But it clearly is the only right way. The fact that everybody else does it some other way only means that they are wrong"

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