homework problem

Requoter · #1 23-Mar-2005, 11:31

Hi everybody! I've been working on this program, that's due tomorrow and I have stumbled upon a problem that I can't figure out.
The program I'm doing suppose to input into the array names, id-numbers and years of service of the employees of non-existent company, the input is about 5 lines total each line looks kinda like this: Jason C. Greenway 642 8, and then I'm suppose to sort it all out by last name, id-number etc. I haven't done the sorting part yet, coz I'm having problems with input file that just wouldn't read into an array. Can anyone tell me what am I doing wrong?
Here's the program:

CPP / C++ / C Code:

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

using namespace std;

int main() 
{ 
	ifstream inData;
	ofstream outData;

	inData.open("lab3.dat");
	outData.open ("lab3.out");

struct Employee
	{
		string firstName;
		string middleInitial;
		string lastName;
		int empNum;
		int yearsofService;
	}   employeeList[10];

	int count = 0;

while (inData)
	{	
		inData >> employeeList[10].firstName >> employeeList[10].middleInitial 
		   >> employeeList[10].lastName >> employeeList[10].empNum 
		   >> employeeList[10].yearsofService;
		count ++;
	}


// Testing the state of the stream
if (!inData)
{
cout << "Can't open the input file." << endl << endl;
return 1;
}

// Output
cout << setw(40) << "Employee's List" << endl << endl;

for (int i = 0; i < count; i++)

{
	cout << setw(9) << employeeList[i].firstName << " " << employeeList[i].middleInitial 
		 << " " << employeeList[i].lastName << " " << employeeList[i].empNum 
		 << " " << employeeList[i].yearsofService << endl;
}

	cout << endl;

	outData << setw(60) << "Employee's List" << endl << endl;
	outData << setw(9) << "Name:" << setw(16) << "ID:" << setw(7) << "Years:" 
		    << endl << endl;

for (i = 0; i < count; i++)

{
	outData << setw(9) << employeeList[i].firstName << " " << employeeList[i].middleInitial 
		    << " " << employeeList[i].lastName << " " << employeeList[i].empNum 
			<< " " << employeeList[i].yearsofService << endl;
}
	inData.close();
	outData.close();

return 0;

}

Thanks in advance for your help.

WaltP · #2 23-Mar-2005, 16:07

You have defines your employee array to hold 10 employees, numbered 0 to 9. When you read the file:

CPP / C++ / C Code:

while (inData)
{	
    inData >> employeeList[10].firstName >> employeeList[10].middleInitial 
           >> employeeList[10].lastName >> employeeList[10].empNum 
           >> employeeList[10].yearsofService;
    count ++;
}

you are reading into the 11th entry in your array for each read. Try changing 10 to count to load the data into the correct array position.

Requoter · #3 23-Mar-2005, 22:37

Quote:

Originally Posted by WaltP

Try changing 10 to count to load the data into the correct array position.

I've tried that before, but it didn't work.

Requoter · #4 25-Mar-2005, 09:36

Quote:

Originally Posted by Requoter

I've tried that before, but it didn't work.

I finally got it done, right before class, and it worked. But the thing I added didn't really make much sense. Turned out that in the for loop I had to put i < count - 1 which meant that it went through the loop 7 times although I only had 5 lines in my data file. Weird...

davekw7x · #5 26-Mar-2005, 08:41

Quote:

Originally Posted by Requoter

Weird...

Well, it's not weird at all, but it is kind of important, since your program shows something that is quite common, and is easy to understand (if you are interested) and easy to fix.

I have abstracted your file reading process to the following:

CPP / C++ / C Code:

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

using std::ifstream;
using std::cout;
using std::endl;
using std::string;

int main()
{
  ifstream inData("test.txt");
  string line;

  while (inData) {  
    inData >> line;
    cout << line << endl;
  }
  return 0;
}

Here is the test.txt file:

CPP / C++ / C Code:

Line1
Line2
Line3

Here is the result of running the program:

Quote:

Line1
Line2
Line3
Line3

The program printed the last line of the file twice. The reason is that the loop condition: while(inData) remains true until after the program has tried to read beyond the end of file. That means that the program runs through the loop after line 3 has been read. Trying to read more yields nothing from the file, but the variable line still has its old value: the last line that was read.

If you want to use this procedure for file reading, you could do something like this:

CPP / C++ / C Code:

  while (inData) {  
    inData >> line;
    if (inData) {
      cout << line << endl;
    }
  }

Now, it only prints if inData is not in its "fail" state (hasn't tried to read past the end of file). The output is this:

Quote:

Line1
Line2
Line3

There may be more elegant and robust ways of reading different things for files, but the principles are the same: test what you got before using it.

Regards,

Dave

WaltP · #6 26-Mar-2005, 09:29

Quote:

Originally Posted by davekw7x

If you want to use this procedure for file reading, you could do something like this:

CPP / C++ / C Code:

  while (inData) {  
    inData >> line;
    if (inData) {
      cout << line << endl;
    }
  }

...

There may be more elegant and robust ways of reading different things for files, but the principles are the same: test what you got before using it.

Not saying this is better, it's just different:

CPP / C++ / C Code:

inData >> line;
do
{
    cout << line << endl;
    inData >> line;
} while (inData);

This does assume there is at least one line in the file. If not, this also has problems so yo can put the if around the do/while.

One reason I like this is it removes the if from the processing loop so only one comparison is needed. The thing I don't like is you have to set up two reads.

davekw7x · #7 26-Mar-2005, 09:39

Quote:

Originally Posted by WaltP

Not saying this is better, it's just different:

One reason I like this is it removes the if from the processing loop so only one comparison is needed. The thing I don't like is you have to set up two reads.

Actually, I rarely use either type. More often it's something like this:

CPP / C++ / C Code:

  while(getline(inData, line)) {
    // typically do something more useful with the input line here
    cout << line << endl;
  }

But I did want to illustrate the point about reading after the end of the file. Your example is another way. Neither is particularly elegant (as far as my personally-defined sense of elegance goes), but they do show ways of getting it done.

Regards,

Dave

Requoter · #8 28-Mar-2005, 10:35

Now, I'm stuck on a different problem.

In my original program I need to take the printing part and make it a void function, which I have no idea how to do, coz I never really had those before and my book doesn't explain much ;( The main problem is I'm getting confused on declaring parameters for the void function. Plus the structure makes it even more compilcated.

Here's what I've done so far:

CPP / C++ / C Code:

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

using namespace std;

void printIt (ofstream& outData, int, int);

int main() 
{ 
	ifstream inData;
	ofstream outData;

	inData.open("lab3.dat");
	outData.open ("lab3.out");

struct Employee
	{
		string firstName;
		string middleInitial;
		string lastName;
		int empNum;
		int yearsofService;
	}   employeeList[10];

int count = 0;
int i;

// reading data
while (inData)
	{
		inData >> employeeList[count].firstName >> employeeList[count].middleInitial 
		   >> employeeList[count].lastName >> employeeList[count].empNum 
		   >> employeeList[count].yearsofService;
	count++;
	}

printIt (outData, count, i);

inData.close();
outData.close();

return 0;
}

void printIt (ofstream& outData, int count, int i)

{

struct Employee
	{
		string firstName;
		string middleInitial;
		string lastName;
		int empNum;
		int yearsofService;
	}   employeeList[10];

count = count--;

	cout << setw(25) << "Employee List:" << endl << endl;
	cout << setw(9) << "Name:" << setw(18) << "ID:" << setw(8) << "Years:" 
		    << endl << endl;

for (i = 0; i < count ; i++)

{
	cout << setw(9) << employeeList[i].firstName << " " << employeeList[i].middleInitial 
		 << " " << employeeList[i].lastName << "   " << employeeList[i].empNum 
		 << "    " << employeeList[i].yearsofService << endl;
}

	cout << endl;

	outData << setw(25) << "Employee List:" << endl << endl;
	outData << setw(9) << "Name:" << setw(18) << "ID:" << setw(8) << "Years:" 
		    << endl << endl;

for (i = 0; i < count ; i++)

{
	outData << setw(9) << employeeList[i].firstName << " " << employeeList[i].middleInitial 
		    << " " << employeeList[i].lastName << "   " << employeeList[i].empNum 
			<< "    " << employeeList[i].yearsofService << endl;
}

}

it actually compiles it and all I get is this warning warning C4700: local variable 'i' used without having been initialized, but when I execute it here's what my my output looks like:

Employee List:

Name: ID: Years:

-858993460 -858993460
-858993460 -858993460
-858993460 -858993460
-858993460 -858993460
-858993460 -858993460

Where did I screw up?

WaltP · #9 28-Mar-2005, 14:16

The problem I believe is you redefined employeeList[] in the function so you are printing out bogus values. You need to pass the structure as a parameter to printIt().

Requoter · #10 28-Mar-2005, 22:39

Quote:

Originally Posted by WaltP

You need to pass the structure as a parameter to printIt().

That did it. Thanks!

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