Read from file, output random line

I have some of the code written down already, but I just don't know how I am going to display one line. I know how to use rand srand, and open a file, but I don't know how to cout just one line.

I am really confused as to what to do. I've tried Google, but I don't know what I'm searching for so I'm getting horrible results.

The code I have is:

Code:

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#include <iostream>
#include <fstream>
#include <cstblib>
#include <conio.h>
#include <ctime>

using namespace std;

int var();
int defu();

int main()
{
        int choice;

        cout << "1.  Open a variable file"        << endl
            << "2.  Open the default file"        << endl
            << "Enter your choice: ";
                cin >> choice;

                switch ( choice )
                {
                        case 1:
                        {
                                var();
                                break;
                        }

                        case 2:
                        {
                                defu();
                                break;
                        }

                        default:
                        {
                                cout << "Invalid choice!" << endl
                                    << "Program closing...";
                                break;
                        }
                }

        getch();
        return 0;
}

var()
{
        // initialize variables
        srand ( ( unsigned ) time ( 0 ) );
        string filename;
        int line-n, yn, d;
        int x = 0;

        // prompt user for file
        cout << "Enter the name of the file you wish to open:" << endl;
                getline ( cin, filename );

        // check to see if string is empty
        if ( filename.empty() )
        {
                cout << "ERROR: No file name entered!" << endl;
                return 0;
        }

        // if string isn't empty
        else
        {
                // open file
                inp.open ( filename.c_str() );

                if ( !infile )
                {
                        cout << "ERROR: Unable to open file" << endl;
                        return 0;
                }
                else
                {
                        // perform the line counting
                        while ( !infile.eof() )
                        {
                                x++;
                                line-n = x;
                        }

                        // finaly, pick out a line and display it
                        while ( yn != 1 )
                        {
                                d = ( rand() %line-n ) +1;

                                // this is where I don't know what to do
                                if ( d ==

---

This is my first program in awhile, so don't hate me for the syntax and, probably, numerous errors. Also, sorry for the indenting; it looks good in vi.

getline() can be used to read in one line of a file--just like reading in one line from cin:

getline(infile, str);


It doesn't matter what ifstream you read from: cin or infile. So, I think the first thing you need to do is get a count of how many lines are in the file:

Code:

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int count = 0;
while( getline(infile, str) )
{
    ++count;
}

---

Note: whenever you read from a file, you want to make your read statement the while loop conditional. That ensures that if there is an error while reading from the file, then reading from the file will cease without messing up your program. Most of the functions you use to read from a file return the ifstream object, e.g. infile, which will evaluate to false if there is an error--that includes eof which is considered a stream error.

Once you have a count of the number of lines, then you can choose your random number. Once you have your random number, you can read one line at a time again until you get to that line number. However, that means you end up reading from the file twice, and reading from files is pretty slow, so you want to avoid doing it whenever possible.

A better solution would be: while you are counting the lines, put each line in a string array(or even better a vector), and then after you are done counting, you will have all the input in the array. That will allow you to access a specific array element using your random number as the index value, which also means you won't have to trudge through every line to get to the line you want.

Is this a typo?

Code:

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#include <cstblib>

---

:p

I hate to badger, but how would I go about entering each string into an array?

Bajanine: Probably... I put a lot of headers, I must have had a plan for it. Too bad I can't think of what it is now.

No, what Bajanine means is that

Code:

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#include <cstblib>

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should probably be

Code:

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#include <cstdlib>

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Quote:

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how would I go about entering each string into an array?

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You would use a loop. And an array of strings. Something like this:

Code:

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string s[10];

for(int x = 0; x < 10; x ++) cin >> s[x];

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Ah hah, thanks guys.

I'll start working on it now.