CODEWITHSUNDEEP
c++data-structureserror-handlingstack
Shubham Kumar
Shubham Kumar

Reputation: 13

Wrote a C++ code to check if expression has balanced parenthesis and my code is not running. I have been stuck for a day now

The code is given below. There is no syntax error and the code used to run perfectly fine if i checked match for only () parenthesis but after i added some if.. else.. statements to check match for other brackets, my code broke. I am unable to figure out my mistake. Please Help!! I think i did some silly mistake but can't figure out what.

// structure of a stack

struct stackStructure
{
    // top pointer of the stack
    int top;
    // pointer to the array/stack
    char *array;
}stack;

// function to push element to stack

void push(char data)
{
    if(stack.top == 999)
    {
        cout<<"Stack Overflow"<<endl;
        return;
    }
    else
    {
        // incrementing the top and then pushing data to the stack
        stack.top++;
        stack.array[stack.top]= data;
    }
} // end of push() function

// function to pop elements from the stack

char pop()
{
    if(stack.top == -1)
        return '\0';
    else
        // returning the popped value and then decrementing the top pointer
        return stack.array[stack.top--];
} // end of pop() function
int main()
{
    // match variable to keep track that closing bracket and opening brackets are in sequence
    char match= '\0';
    bool isMatching= true;
    // resetting the stack variables and attributes
    stack.top= -1;
    stack.array= new char[1000];
    cout<<"Enter the Expression to match the parenthesis: ";
    cin>>stack.array;

    // traversing through the character array and matching parenthesis
    for(int i=0; stack.array[i] != NULL; i++)
    {
        // if character is an opening bracket
        if(stack.array[i] == '(' || stack.array[i] == '{' || stack.array[i] == '[')
            push(stack.array[i]);
        // if character is a closing bracket
        else if(stack.array[i] == ')' || stack.array[i] == '}' || stack.array[i] == ']')
        {
            match= pop();
            if(stack.array[i] != match)
                isMatching= false;
        }
        // if character is anything else we do nothing
        else
            continue;
    }
    if(isMatching == true)
        cout<<"Parenthesis Matched"<<endl;
    else
        cout<<"Not matched"<<endl;
    return 0;
}

Upvotes: 1

Views: 222

Answers (1)

Alan Birtles
Alan Birtles

Reputation: 36379

You have 2 bugs. The first is reading your input string into your stack, this will at minimum get very confusing and at worst not work.

The second is that when checking for matching tags you check that the opening bracket is the same as the closing one, this will never be true, you need to check that the opening bracket is the same type as the closing one.

One way of solving both bugs would be:

int main()
{
    // match variable to keep track that closing bracket and opening brackets are in sequence
    char match = '\0';
    bool isMatching = true;
    // resetting the stack variables and attributes
    stack.top = -1;
    stack.array = new char[1000];
    std::string input;
    cout << "Enter the Expression to match the parenthesis: ";
    cin >> input;

    std::map<char, char> opening = { { ')', '(' }, { '}', '{' }, { ']', '[' } };

    // traversing through the character array and matching parenthesis
    for (char ch : input)
    {
        // if character is an opening bracket
        if (ch == '(' || ch == '{' || ch == '[')
            push(ch);
        // if character is a closing bracket
        else if (ch == ')' || ch == '}' || ch == ']')
        {
            match = pop();
            auto open = opening.find(ch);
            if (open == opening.end() || open->second != match )
                isMatching = false;
        }
    }
    if (isMatching == true)
        cout << "Parenthesis Matched" << endl;
    else
        cout << "Not matched" << endl;
    delete[] stack.array;
    return 0;
}

Upvotes: 1

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