c plus plus strings for loops and if statements.

[Jaggy1997]

I am working on a project where you make a txt file and you are suppose to print out 10 lines. If one line is empty it is also suppose to be printed out and counted as one line. So we can have 1000 lines in there but it is only gonna print out 10 lines in a row. If input == yes it is gonna print out 10 more lines.

#include <iostream>
#include <fstream>
#include <string>
using namespace std;
const int MAX = 5;
int main()
{
string str;
ifstream fin;

for(int i = 0; i < MAX; i++)
{
fin.open("DataTextFile.txt");
if (fin.is_open())
{

while(!fin.eof())
{
getline(fin, str);
cout << str << endl;

}
fin.close();
}


else {
cout << "unable to read from file!" << endl;

}
}

return 0;
}

[AbstractionAnon]

I'm not sure what your question is.

Line 13: You're opening the input file 5 times.

Line 17: Do not loop on (! stream.eof()) or (stream.good()). This does not work the way you expect. The eof bit is set true only after you make a read attempt on the file. This means after you read the last record of the file, eof is still false. Your attempt to read past the last record sets eof, but you're not checking it there. You proceed as if you had read a good record. This will result in reading an extra (bad) record. The correct way to deal with this is to put the >> (or getline) operation as the condition in the while statement.

  while (stream >> var) // or while (getline(stream,var))
  {  //  Good operation
  }

PLEASE ALWAYS USE CODE TAGS (the <> formatting button) when posting code.
It makes it easier to read your code and also easier to respond to your post.
http://www.cplusplus.com/articles/jEywvCM9/
Hint: You can edit your post, highlight your code and press the <> formatting button.

[Handy Andy]

Hello Jaggy1997,

PLEASE ALWAYS USE CODE TAGS (the <> formatting button) when posting code.
It makes it easier to read your code and also easier to respond to your post.
http://www.cplusplus.com/articles/jEywvCM9/
http://www.cplusplus.com/articles/z13hAqkS/
Hint: You can edit your post, highlight your code and press the <> formatting button.
You can use the preview button at the bottom to see how it looks.

You say:

So we can have 1000 lines in there but it is only gonna print out 10 lines in a row.

OK which ten lines? The first ten? The last ten? Or a random ten? Printing the first tn is easy.

Your program has most of the right pieces, but will not work this way.

Your while loop condition is not the way to check for end of file. Checking for "eof" does not work the way you think it will. The while loop will print out 1001 lines not the 1000 in the file. By the time the while conditions understands that you have reached "eof" the last line read will print twice. The more common way of writing the while condition is: while(std::getline(fin, str)). This way when the stream fails so does the while loop.

If you only want to print ten lines the while loop needs away to count the number of lines printed and break out of the while loop when the count has reached ten.

The for loop in unnecessary because it will print the ten lines you need five times before it is finished. Not what you want.

The following code is yours and has some notes in worth reading:

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

//using namespace std;  // <--- Best not to use.

const int MAX = 5;

int main()
{
	std::string str;
	std::ifstream fin;

	for (int i = 0; i < MAX; i++)
	{
		fin.open("DataTextFile.txt");  // <--- Should be above for loop.
		if (fin.is_open())  // <--- This check should be done above for loop.
		{

			while (!fin.eof())
			{
				std::getline(fin, str);
				std::cout << str << std::endl;

			}
			fin.close();
		}


		else {
			std::cout << "unable to read from file!" << std::endl;

		}
	}

	return 0;
}

That should be enough to keep you working for awhile. Any questions just ask.

Hope that helps,

Andy