Thread: help me with files

You probably want to read a string, rather than a single character. If you use the "std::string" or a char array is up to you.

You don't seem to suplly any code for this:
You ask the user where he wants the results to be stored
The user types a file name
Your program opens that file for output
Your program writes in that file the result that you had already calculated in step 4
Close the output file
Inform the user that the task was completed
When the user hits ENTER terminate the program

You are counting the number of numbers in the file [incorrectly, as you count each number twice] - and you don't actually detect when the end of file is reached. So this part of your task is incorrect.
If the user types the correct file name your program reads the numbers from that file one by one while it keeps a running total

Your file validation seems to be correct to me. Does it work? [Obviously, you are currently using a constant in your open() call, "num.txt", and that would need to change so that it uses a variable that the user inputs - like the f variable once you've made it into a string]

--
Mats

changed a few things just now

Code:

//
//
//
//

#include <iostream.h>
#include <fstream.h>
#include <ios.h>

int main()
{
	char inf[50];
	char outf[50];
	int number;
	int count=1;
	ifstream infile;
	ofstream outfile;
	
	cout << "What is the name of the file you want to read from?"<<endl;
	cin >> inf;
	
	infile.open(inf, ios::nocreate);
	if (infile.fail())
		cout << "error opening file";
	else
	{
		while (count<=number)
		{
			infile >> number;
			count++;
		}
		cout << count;
		infile.close();
	}
	cout << "what file do you want me to store the count in?";
	cin >> outf;
	
	outfile.open(outf, ios::nocreate);
	if (!outfile)
	{	
		cout << "error opening file";
		return 0;
	}
	else
	{
		outfile << count;
	}
	return 0;
}

I'm pretty sure that your result should be the sum of the numbers in the file, and your read-loop is still broken on two accounts:
1. It doesn't detect failing to read.
2. It counts up twice (once inside the while condition and once in the loop itself).

--
Mats

Ah, yes, I didn't think it through very far - if your count is zero the first time round, then you don't even enter the loop, so nothing is ever read from the file.

So, what do you think you should do if:
1. You want to read a number from the file for as long as it's possible.
2. Sum up the numbers you read into a sum variable.

[You can count the number of them too if you like, but that's not what I thought the task was supposed to do].

--
Mats

First of all, those are two distinct problems:
- Produce the sum of all the numbers. [There is absolutely no requirement that you have given that says "Produce a count of the numbers"].

- Write the data to a user-specified output file. The code you have is good for asking the user and creating a file - all that remains is to produce the data [whcih of course depends on the above].


You may find this helpful:
When you use a statement like:
infile >> number;
it produces a "result" of "success" or "fail", where "fail" is "false".

--
Mats

Code:

while (count << number)

will shift your count by "number" bits to the left as a binary operator. This is NOT what you want to do here. In my example, the left-hand operand of the << operator is a stream, not an integer variable - this is one of the tricky things in C++ - something that looks like it does one thing with simple variables can do something completely different with OTHER inputs.

--
Mats

What do you think it should be? Something where the left operand of the >> is a filestream, right? And what are you doing using a filestream already?

--
Mats

So look at your code, and look at what the types are. Do you find anything that is a filestream of some sort?

--
Mats