(easy to answer [hopefully]) College student needs help debugging one line of code.

Hi, I'm not sure if this is the correct place to post, or if posting for help debugging is even allowed (as this is my first post). If I'm in the wrong, let me know.

But! I need help debugging my code! I've narrowed it down (through error catching) to one line of code. The code where the program stops is in my placeInto() function, which is called from my convert() function. I've tried making this program easily readable (going as far as numbering my functions!). Now the pointless effort might have a point after all.
Any ideas?

Code:

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/*
This code was created by Brandon *****.
The program is an RPN Calculator, designed to receive keyboard input of an infix mathematical string, convert
the infix string into a postfix mathematical string, and then solve the string. The program then outputs the
postfix string and the solution.
The program loops through until closed via force-close, as was assigned.
*/

#include <iostream>
#include <string>
#include <stack>
using namespace std;
 
 ///////////////////////
// function prototypes //
 ///////////////////////

// u = unfinished
/*  1*/void welcome(); // welcome screen
/*  2*/bool input(); // prompt for input (infix string). If returns false, invalid input. (only numbers, parens, spaces, and - + * / allowed.)
/*  3*/void convert(); // convert infix string to postfix string
/*  4*/int  solve(); // solve the postfix string. This is used in (5)output().
/*  5*/void output(); // output the postfix string and the result. The result is calculated in output() via (4)solve().
/*  6*/void reset(); // reset global values to NULL
/*  7*/bool isValid(char); // used in (2)input() to check for iChar's validity. If returns false, (2)input() also returns false.
/*  8*/void invalidInput(); // used if (2)input() returned false. Explains to the user: try again.
/*  9*/bool isDigit(char); // used in (3)convert() to determine whether inString[i] is a digit. Returns true: is a digit.
/* 10*/bool isOperand(char); // used in (3)convert() to determine whether inString[i] is an operand. Returns true: is an operand.
/* 11*/void unStack(stack<char> &, int &); // used in (3)convert() to "unstack" (remove all operators from a stack and append them to global-postString). Needs to increment postCount with each append.
/* 12*/void placeInto(stack<char> &, char, int &); // used in (3)convert() to correctly push an item into a select stack. (cannot have <operands in the stack ontop of >operands)
/* 13*/int  opValue(char); // return a value for a char operator. values: -(1) +(2) *(3) /(4).. used in (4)solve()
/* 14*/int  toNum(char); // take in a char digit, spit out the cooresponding decimal digit.. used in (4)solve()

/* Notes
/* u = unsolved
/* s = solved
/u/ Referring to parenStack in (3)convert(): need to make more dimensions of inParens (which means more parenStack's).
    If possible, would be nice to: stack<char> parenStack[5]; and turn inParens into an int,
    the value of which would pertain to the current dimension of parenStack.
/u/ Referring to the usage of solve() in (5)output(): might be unable to cout << solve();
    if so, int result = solve(); cout << result;
*/

 ////////////////////
// global variables //
 ////////////////////

char
    inString[100] = {NULL}, //infix string, contains no spaces.
    postString[100] = {NULL}; //postfix string, converted from infix string in (3)convert().


 ////////////////////
// main() ////////////

int main()                                 
{                                           
    welcome();                         
    while(1 < 2)                           
    {                                     
        if(input())                 
        {                                 
            cout << "Before convert()" << endl;
            convert();
            cout << "Before output()" << endl;               
            output();           
        }                                   
        else                             
            invalidInput();         
       
        cout << "Before reset()" << endl;                                       
        reset();                                     
    }                                               
    return 0;                                         
}       
                                             
// End of main() /////
 ////////////////////


 ////////////////////////
// Function definitions //
 ////////////////////////
 
/* 1*/void welcome()
{
    cout << "Welcome to Brandon's RPN Calculator!" << endl
          << "Input an infix mathematical string to have it converted to RPN and solved!" << endl
          << "Valid characters: single digits - + * / ) ( and space" << endl
          << endl
          << "Press ctrl-c at any time to exit." << endl
          << endl;
         
          system("PAUSE");
          system("CLS");
}

/* 2*/bool input()
{
      char tempString[250] = {NULL};
      int inCount = 0;
     
      cout << "Input your infix string:" << endl
            << "? ";
      cin.getline(tempString, 250);
      for(int i = 0; (tempString[i] != NULL); i++)
      {
            if(!isValid(tempString[i]))
                  return false;
                 
            if(tempString[i] != ' ')
            {
                  inString[inCount] = tempString[i];
                  inCount++;
            }
      }
      return true;
}

/* 3*/void convert()
{
int isDigits = 0;
    int
        postCount = 0;
    bool
        inParens = false;
    stack<char> opStack;
    stack<char> parenStack;
    for(int i = 0; (inString[i] != NULL); i++)
    {
            if(inString[i] == '(')
                  inParens = true;
            else
                if(inString[i] == ')')
                {
                      inParens = false;
                      unStack(parenStack, postCount);
                }
                else
                    if(isOperand(inString[i]))
                    {
                    cout << "isOperand." << endl;
                          if(inParens)
                              placeInto(parenStack, inString[i], postCount);
                          else
                              placeInto(opStack, inString[i], postCount);
                              cout << "isOperand end." << endl;
                    }
                    else
                        if(isDigit(inString[i]))
                        {
                                                isDigits++;
                        cout << "isDigit. " << isDigits << endl;
                              postString[postCount] = inString[i];
                              postCount++;
                        }     
    }
    cout << "before unstack" << endl;
    unStack(opStack, postCount);
    cout << "after unstack" << endl;
}

/* 4*/int solve()
{
          stack<char> solveStack;
          int
              int1,
              int2;
             
          for(int i = 0; (postString[i] != NULL); i++)
          {
                  if(isDigit(postString[i]))
                        solveStack.push(toNum(postString[i]));
                  else
                  {
                      int2 = solveStack.top();
                      solveStack.pop();
                      int1 = solveStack.top();
                      solveStack.pop();
                      switch(postString[i])
                      {
                      case '-':
                            if(!solveStack.empty())
                                solveStack.push(int1 - int2);
                            else
                                return int1 - int2;
                            break;
                      case '+':
                            if(!solveStack.empty())
                                solveStack.push(int1 + int2);
                            else
                                return int1 + int2;
                            break;
                      case '*':
                            if(!solveStack.empty())
                                solveStack.push(int1 * int2);
                            else
                                return int1 * int2;
                            break;
                      case '/':
                            if(!solveStack.empty())
                                solveStack.push(int1 / int2);
                            else
                                return int1 / int2;
                            break;
                      }
                  }
          }
}

/* 5*/void output()
{
          cout << "Postfix String:" << endl
                << postString << endl
                << endl
                << "Result:" << endl
                << solve() << endl
                << endl;
}

/* 6*/void reset()
{
    system("PAUSE");
    system("CLS");
    for(int i = 0; (inString[i] != NULL); i++)
            inString[i] = NULL;
    for(int i = 0; (postString[i] != NULL); i++)
            postString[i] = NULL;   
}

/* 7*/bool isValid(char iChar)
{
    switch(iChar)
    {
    case ' ':
    case '(':
    case ')':
    case '-':
    case '+':
    case '*':
    case '/':
    case '0':
    case '1':
    case '2':
    case '3':
    case '4':
    case '5':
    case '6':
    case '7':
    case '8':
    case '9':
          return true;
    default:
          return false;
    }
}

/* 8*/void invalidInput()
{
    cout << "Invalid input detected." << endl
          << "Please input only legal characters:" << endl
          << "single digits - + * / ) ( and space" << endl
          << endl;   
}

/* 9*/bool isDigit(char iChar)
{
          switch(iChar)
          {
                case '0':
                case '1':
                case '2':
                case '3':
                case '4':
                case '5':
                case '6':
                case '7':
                case '8':
                case '9':
                    return true;
                default:
                    return false;
          }
}

/*10*/bool isOperand(char iChar)
{
          switch(iChar)
          {
                case '-':
                case '+':
                case '*':
                case '/':
                    return true;
                default:
                    return false;
          }
}

/*11*/void unStack(stack<char> & iStack, int & postCount)
{
          while(!iStack.empty())
          {
                postString[postCount] = iStack.top();
                postCount++;
                iStack.pop();
          }
}

/*12*/void placeInto(stack<char> & iStack, char iChar, int & postCount)
{
          cout << "before while of placeinto" << endl;
          while(opValue(iStack.top()) > opValue(iChar)) ///////This is where the program stops.
          {
                cout << "inside while of placeinto" << endl;
                postString[postCount] = iStack.top();
                postCount++;
                iStack.pop();
          }
          cout << "after while of placeinto" << endl;
          iStack.push(iChar);
}

/*13*/int opValue(char iChar)
{
          cout << "before switch of opValue" << endl;
          switch(iChar)
          {
          case '-':
              return 1;
          case '+':
              return 2;
          case '*':
              return 3;
          case '/':
              return 4;
          }
}

/*14*/int toNum(char iChar)
{
          return (int)iChar - 48;
}

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Quote:

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Originally Posted by Filthy_Utter

Hi, I'm not sure if this is the correct place to post, or if posting for help debugging is even allowed (as this is my first post). If I'm in the wrong, let me know

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Why not just use the debugger that comes with Visual Studio? Then you aren't hunting down where the problem occurs -- you're actually single-stepping through the program, watching variables, setting breakpoints, etc.

You wrote the program, so whenever the program takes a different path, a variable takes a wrong value, or something you didn't expect happens does happen, you will see it happen and know what to do to fix the problem.

Regards,

Paul McKenzie