Member Avatar for DelilahDemented

My program will process the first and second line of the text file but gets a bit crazy after that. Lines 1, 2, 3, and 5 are supposed to match and line 4 does not. It gets lines 1 and 2 but 3 and 5 are incorrect and it processes a blank line. Not sure how to fix this. All help is greatly appreciated!

input:
()
[](){}
[{()}]
[[))
{()[()]}

output:
( ) 
Parenthesis matched

[ ] ( ) { } 
Parenthesis matched

[ { ( ) } ] 
Parenthesis Not matched

[ [ ) ) 
Parenthesis Not matched

{ ( ) [ ( ) ] } 
Parenthesis Not matched


Parenthesis matched


int main()
  {
    Stack stackLeft;
    char inputArray[20];
    char value;
    int inputCount = 0;
    int countLeft = 0;

    //Open inFile
    inFile.open("StackStr.txt");

    while(!inFile)
    {
        cout << "Error opening the inFile." << endl;
        return 1;
    }

    //Open outFile
    outFile.open("StackResults.txt");

    while(!outFile)
    {
        cout << "Error opening the outFile." << endl;
        return 1;
    }

    while(inFile)
    {
        countLeft = 0;

        inFile.getline(inputArray, 20,'\n');
        inputCount = 0;

        while(inputArray[inputCount]!='\0')
        {
            value = inputArray[inputCount];
            cout << value << " ";
            outFile << value << " ";
            inputCount++;

            if(value=='(' || value=='[' || value=='{')
            {
                stackLeft.push(value);
                countLeft++;
            }
            else if(value==')' || value==']' || value=='}')
            {
                if(stackLeft.top() == '(' && value == ')')
                {
                    stackLeft.pop();
                    countLeft--;
                }
                else if(stackLeft.top() == '[' && value == ']')
                {
                    stackLeft.pop();
                    countLeft--;
                }
                else if(stackLeft.top() == '{' && value == '}')
                {
                    stackLeft.pop();
                    countLeft--;
                }
            }
        }

        if(countLeft == 0)
        {
            cout<<endl<<"Parenthesis matched" << endl << endl;
            outFile<<endl<<"Parenthesis matched" << endl << endl;
        }
        else
        {
            cout<<endl<<"Parenthesis Not matched" << endl << endl;
            outFile<<endl<<"Parenthesis Not matched" << endl << endl;
        }
    }

    system("pause");
    return 0;
  }
  • 2 Contributors
  • 2 Replies
  • 191 Views
  • 18 Hours Discussion Span
  • Latest Post Latest Post by DelilahDemented

Dani AI

Generated

Short summary of what went wrong and how to fix it (references: original code and ’s debugging suggestion).

There are three concrete problems visible in the posted code that explain the stray output and the incorrect results:

  • The outer loop uses the file-stream state instead of checking the result of getline, which can cause an extra iteration and a spurious "matched" print for a blank read.
  • The code calls the stack's top() without first checking whether the stack is empty; calling top() on an empty stack is undefined behavior and will produce unpredictable results.
  • Only the counter is reset between lines; the stack itself is not cleared, so leftover items from previous lines can wreck subsequent checks.

All three should be fixed. Use std::string with std::getline for the read loop, construct or clear a fresh stack for each input line, and always check empty() before using top()/pop(). ’s tip to print the stack top after pushes/pops is a good debugging step — it would have immediately shown an attempt to read top() from an empty stack.

Example (robust) approach:

#include <fstream>
#include <string>
#include <stack>

bool matches(char open, char close) {
  return (open=='(' && close==')') ||
         (open=='[' && close==']') ||
         (open=='{' && close=='}');
}

std::ifstream in("StackStr.txt");
std::ofstream out("StackResults.txt");
std::string line;
while (std::getline(in, line)) {
  std::stack<char> st;
  bool ok = true;
  for (char c : line) {
    if (c=='(' || c=='[' || c=='{') st.push(c);
    else if (c==')' || c==']' || c=='}') {
      if (st.empty() || !matches(st.top(), c)) { ok = false; break; }
      st.pop();
    }
  }
  if (!st.empty()) ok = false;
  out << line << '\n' << (ok ? "Parenthesis matched" : "Parenthesis Not matched") << "\n\n";
}

Notes: if you keep a custom Stack class, add an empty() method or a clear() routine and always check empty() before top(). Debug prints per are useful while verifying fixes.

Recommended Answers

All 2 Replies

Member Avatar for zeroliken

try printing the new top of the stack and next input after every pop/push to have a general view of the problem and see if the current conditions would satisfy the current input and top of stack,

Edited by zeroliken
Member Avatar for DelilahDemented

Thanks for the advice, I fixed it.

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