Functions Problem

I'm having trouble with this homework problem. I know I'm close to having it solved but I can't get the loop to stop. It finds the correct name to the parking sticker in the text file but keeps looping over and over. Here's the problem for a better understanding:

Quote:

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Assume that a file named HWK5.txt has a single name (last name only -- no first name or middle initial) and a parking sticker number (6 digits) on each line of the file. It is unknown how many names are on the file. (You will need to make up a test file to use.) Write a program that will ask the user for a parking sticker number (000000 to stop) and then search the file for that number. When it finds the number in the file, it will write out "This parking sticker belongs to " followed by the corresponding name on the file, or if the sticker number is not found on the file, the message "This parking sticker is not on file. Try again." should be displayed. The program will then ask for another sticker number and repeat until a sticker number of 000000 (or just plain zero) is entered. To perform the search, the parking sticker number should be sent to a function called findName, which you will write. The function findName should open the file HWK5.txt, search it for the given sticker number, and return the corresponding name to the calling program. Before it returns, the function should close the file HWK5.txt so that it will be ready to be used for the next search. If the sticker number is not found on the file, the function should return a value of "NOT FOUND" to the calling program. The function should NOT display anything on the screen; the main function should handle this task, as well as prompting for the next sticker number.

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I'm not understanding the bold portion of the problem and in turn is probably what is causing my trouble. Here is the work I have so far:

Quote:

---

#include <iostream>
#include <fstream>
#include <string>
using namespace std;

int main()
{
string lastName;
double number, target, parkingSticker;
const double SENTINEL = 000000;

cout << "Please enter a parking sticker number (enter 000000 to exit): " << endl;
cin >> target;

while (target != SENTINEL)
{
ifstream input("HWK5.txt");
if (input.is_open())
{
while (! input.eof())
{
input >> lastName >> parkingSticker;
if (target == parkingSticker)
cout << "The parking sticker number belongs to " << lastName << endl;
else
cout << "This parking sticker is not on file. Try again." << endl;
}
}
input.close();
}
system("pause");
return 0;
}

---

The function is working correctly as far as finding the correct name to the parking sticker number. It just displays:

Quote:

---

The parking sticker number belongs to Smith
This parking sticker is not on file. Try again.
The parking sticker number belongs to Smith
This parking sticker is not on file. Try again.
The parking sticker number belongs to Smith
This parking sticker is not on file. Try again.

---

::repeats this over and over::

Just wondering how I'm suppose to stop it from looping over and over and not display the second message if it actually finds the parking sticker number. Any help would be greatly appreciated.

Code:

---


#include <iostream>
#include <fstream>
#include <string>
using namespace std;

int main()
{
    string lastName;
    double number, target, parkingSticker;
    const double SENTINEL = 000000;
   
    cout << "Please enter a parking sticker number (enter 000000 to exit): " << endl;
    cin >> target;
   
    while (target != SENTINEL)
    {
          ifstream input("HWK5.txt");
          if (input.is_open())
          {
            while (! input.eof())
            {
                  input >> lastName >> parkingSticker;
                  if (target == parkingSticker)
                      cout << "The parking sticker number belongs to " << lastName << endl;
                  else
                      cout << "This parking sticker is not on file. Try again." << endl;
            }
          }
          input.close();
    }
    system("pause");
    return 0;
}

---

A better view of the code I have so far.

The bold part of the assignment means, you should write a function like this:

Code:

---

std::string find(const std::string& sticker) {
  // open file
  // search file for sticker
  // if found, return lastname
  // if not found, return "NOT FOUND"
}

---

In turn, your main function should be reduced to:

Code:

---

int main()
{
    const double SENTINEL = 000000;

    for (;;) {   
        std::cout << "Please enter a parking sticker number (enter 000000 to exit): " << std::endl;
        std::cin >> target;
        if (target == SENTINEL) break;   
        std::cout << find(target) << std::endl;
    }
}

---

About your current code. A typical mistake is the following:

Code:

---

            while (! input.eof())
            {
                  input >> lastName >> parkingSticker;

---

input.eof() is only set after the end of file has been read, so your program will execute the loop one time too many. Instead, use the following:

Code:

---

while (input >> lastName >> parkingSticker) {

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Another thing: How many times should the user be asked for a sticker number and how often is he asked in your program?

Just a note. It's generally not a very good idea to compare floats and doubles for equality using ==.

Quote:

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Originally Posted by nuzzle

Just a note. It's generally not a very good idea to compare floats and doubles for equality using ==.

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True and the parking sticker should be neither one nor an int. It should be a string !!

Thanks guys for the responses but I'm still not getting this so I asked for help from my professor. This is what he had to say:

Quote:

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The variable parkingSticker should be declared a double, not a string. You should also have the while loop for the sentinel as the outside loop, not the inside loop. The sentinel-controlled loop should have everything else in it, including the open and close commands. The loop on file input should (which is end-of-file controlled) should keep comparing the target to the parkingSticker until either you reach the target or hit the end of the file. You will need some bool variable to set so that you know you have found the target and can quit looking.

---

I have had parkingSticker declared as a double and I switched the while loop to be the outside one. This was all done before I made this thread. Guess what I'm having trouble with is the bool variable thing. I just can't get the loop to stop looking after it's already found. Anymore help would be greatly appreciated.

Some hints:

Code:

---

    while (target != SENTINEL)

---

The condition for your while loop compares target and SENTINEL. Neither one of the variable is changed inside the while loop. Thus the loop, if entered, does not have a possibility to terminate.

Code:

---

            while (! input.eof())
            {
                  input >> lastName >> parkingSticker;
                  if (target == parkingSticker)
                      cout << "The parking sticker number belongs to " << lastName << endl;
                  else
                      cout << "This parking sticker is not on file. Try again." << endl;
            }

---

The while loop iterates (wrongly as I pointed out earlier) over each line of the file. Thus a line is printed out for each line in the search file. But what you actually want is first to search through the file and after you are done, print a line if the search was successful or not.

Quote:

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Originally Posted by Ruined Embrace

This is what he had to say:

Quote:

---

Originally Posted by professor

The variable parkingSticker should be declared a double, not a string.

---

---

Ask him why! So you can divide two parking sticker numbers by each other? Or so that the square root of one parking sticker results in another parking sticker? Or is it just to ensure that comparing two parking sticker numbers does not necessarily return the correct result. Maybe there's a relationship between the gravity of a planet and a parking sticker number? I'll be intrigued to know...

Quote:

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Originally Posted by Ruined Embrace

The variable parkingSticker should be declared a double, not a string

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Sometimes, I wonder where in the world these teachers are coming from.

Quote:

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Just wondering how I'm suppose to stop it from looping over and over and not display the second message if it actually finds the parking sticker number.

---

This is trivial. Just make your while loop only execute if a ticket is not found.

Code:

---

bool foundTicket = false;
while (I have stuff to input && !foundTicket )
{
    if ( I've found a ticket )
    {
        do stuff when ticket is found
        Now set foundTicket to the right value to stop the loop
    }       
}

---

Regards,

Paul McKenzie

Quote:

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Originally Posted by treuss

Some hints:

Code:

---

    while (target != SENTINEL)

---

The condition for your while loop compares target and SENTINEL. Neither one of the variable is changed inside the while loop. Thus the loop, if entered, does not have a possibility to terminate.

---

I have to keep everything in that. I have to give the user a way to exit the program and that's by the SENTINEL value. I'm still trying to figure out this boolean thing. I graduated a two year school with over a 3.0 GPA and I've never had a subject this hard. The book is not user friendly at all and the teacher is horrible. I've sat on this project for 3 hours every night trying to figure it out. Here it is, a week past due and I'm not even sure he'll accept it when I get finished. There's no example even close to this project in the book. Hell, reading from a text file isn't even in this book until Chapter 13 and we just now got to Chapter 7 in class.

Quote:

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Originally Posted by Ruined Embrace

I have to keep everything in that.

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I don't know what that's supposed to mean.

Quote:

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I have to give the user a way to exit the program and that's by the SENTINEL value. I'm still trying to figure out this boolean thing.

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Did you read my post? Without giving you the code verbatim, it should have answered your question.

Quote:

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Also, I graduated a two year school with over a 3.0 GPA and I've never had a subject this hard.

---

What subjects? Was your major based on cold logical reasoning (as computer programming and computer science is) or on some other criteria? Some brilliant people who excel in other topics can't for the life of them write a computer program -- it has nothing to do with intelligence, their brains are just not wired to follow or devise a set series of steps (i.e. algorithm).

Quote:

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The book is not user friendly at all

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What is the name of the book? You know that this is your opinion -- the book may not be user-friendly to you, but may be a piece of cake to someone else.

Regards,

Paul McKenzie

Think I'm pretty close to solving this now. Anymore help would be greatly appreciated.

Code:

---

#include <iostream>
#include <fstream>
#include <string>
using namespace std;

int main()
{
    string lastName;
    double number, target, parkingSticker;
    const double SENTINEL = 000000;
   
    cout << "Please enter a parking sticker number (enter 000000 to exit): " << endl;
    cin >> target;
   
    while (target != SENTINEL)
    {
          bool found = false;
          string foundName = "NOT FOUND";
         
          ifstream input("HWK5.txt");
          if (input.is_open())
          {
           
            input >> lastName >> parkingSticker;
            while (! input.eof() && !found)
            {
                  if (target == parkingSticker)
                  {
                      foundName = lastName;
                      found = true;
                  }
            }
          }
          input.close();
          return foundName;
    }
    if (lastName != "NOT FOUND")           
      cout << "The parking sticker number belongs to " << lastName << endl;
    else
      cout << "This parking sticker is not on file. Try again." << endl;
             
    system("pause");
    return 0;
}

---

I'm getting an error on the "return foundName;" part. It's telling me that it can't convert string to integer. I have to return something though. Think that's the only part that's holding me back.

Since you're in main(), there's no point in returning anything other than 0.

Also, you still are never modifying target within the while loop; thus the loop can never end once it is entered.

You stated in your first post that the exercise involves

Quote:

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Originally Posted by Ruined Embrace

a function called findName, which you will write

---

I still don't see any function in your code. The function will make your code easier, not more complex, so it is time to get it in. Do it. Now.

Code:

---

#include <iostream>
#include <fstream>
#include <string>
using namespace std;

int main()
{
    string lastName;
    double number, target, parkingSticker;
    const double SENTINEL = 000000;
   
    cout << "Please enter a parking sticker number (enter 000000 to exit): " << endl;
    cin >> target;
   
    while (target != SENTINEL)
    {
          string findName(int foundName)
          {
            bool found = false;
            string foundName = "NOT FOUND";
         
            ifstream input("HWK5.txt");
            if (input.is_open())
            {

                input >> lastName >> parkingSticker;           
                while (! input.eof() && !found)
                {
                    if (target == parkingSticker)
                    {
                        foundName = lastName;
                        found = true;
                    }
                  input >> lastName >> parkingSticker;                   
                }
            }
          input.close();
          return foundName;
          }
    }
    if (foundName != "NOT FOUND")           
      cout << "The parking sticker number belongs to " << lastName << endl;
    else
      cout << "This parking sticker is not on file. Try again." << endl;
             
    system("pause");
    return 0;
}

---

Still many problems. :(

You are still not using a function. You use a return statement, you have no function except main to return from. Your book or lecture notes must have an example for a function. Read it. Understand it. Then look again at Post #3 above.

You are still having a condition while (target != SENTINEL) but don't change either value in the loop. The condition can thus be only "always true" or "always false" thus making little sense.

After days and days of slaving, I think I finally have something that works. You guys see any corrections I could make to this?

Code:

---

#include <iostream>
#include <string>
#include <fstream>

using namespace std;

string findName(int parkingSticker);

int main ()
{
    int target = 0;
    const double SENTINEL = 000000;
    //string functionMessage = "";

    cout << "Please enter a parking sticker number (enter 000000 to exit): " << endl;
    cin >> target;
 
    while (target != SENTINEL)
    {
          if  (findName (target) == "NOT FOUND")
          {
              cout << "This parking sticker is not on file. Try again." << endl << endl;
          }
          else
          {
              cout << "This parking sticker belongs to " << findName(target) << endl << endl; 
          }
         
          cout << "Please enter a parking sticker number (enter 000000 to exit): " <<endl;
          cin >> target; 
    }
 
    system ("pause");
    return 0;
 
}

string findName (int parkingSticker)
{
    string name;
    int tempNum;
    string returnValue = "";
    ifstream input;
    input.open("HWK5.txt"); 
 
    input >> name >> tempNum;
    while (!input.eof())
    {
            if (parkingSticker == tempNum)
            {
                      returnValue = name;
                      break;
            }               
            else if (parkingSticker != tempNum)
            {
                input >> name >> tempNum;
             
            } 
    }

    if (returnValue == "")
    {
        returnValue = "NOT FOUND";             
    }

    return returnValue;

}

---

Quote:

---

Originally Posted by Ruined Embrace

You guys see any corrections I could make to this?

---

Not corrections, but a misunderstanding of what a double means:

Code:

---

    const double SENTINEL = 000000;

---

Those extra 0's do nothing except wear out your keyboard. This is exactly the same as this:

Code:

---

const double SENTINEL = 0.0;

---

Why is SENTINEL a double anyway? Since target is an int, then SENTINEL should be an int.

Regards,

Paul McKenzie

I'm not sure man. My professor is kind of strange. He demands we use const double SENTINEL = 000000

Code:

---

    input >> name >> tempNum;
    while (!input.eof())
    {
            if (parkingSticker == tempNum)
            {
                      returnValue = name;
                      break;
            }               
            else if (parkingSticker != tempNum)
            {
                input >> name >> tempNum;
             
            } 
    }

---

A better way to write this would be:

Code:

---

    while (input >> name >> tempNum)
    {
            if (parkingSticker == tempNum)
            {
                      returnValue = name;
                      break;
            }               
    }

---

Another improvement I could think of would be to initialize returnValue with "NOT FOUND" and not with an empty string. This would save the check after the loop.

I suppose that if you were not concerned about trying for a single point of return, the returnValue variable could be easily eliminated:

Code:

---

while (input >> name >> tempNum)
{
    if (parkingSticker == tempNum)
    {
        return name;
    }
}
return "NOT FOUND";

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