Read from files

cvirus · #1 09-Jun-2007, 14:30

CPP / C++ / C Code:

#include <cstdlib>
#include <iostream>
#include <fstream>

using namespace std;

int n;

void input_output()
{   
    ifstream input("c:\\file_in.txt");
    ofstream out("c:\\file_out.txt");
    while (input>>n)
    {
input>>n;
    out<<"\n"<<n<<endl;
    }
    input.close();  
}

int main()
{
input_output(); 
      system("PAUSE");
}

Hello, i´ve done this code and i ve create in my c drive the input file, what i want to know is : how can i pic the numbers in the input file and then make the calculations and send to the output file.

Thank you

dlp · #2 09-Jun-2007, 19:09

We need more information about what exactly you are trying to do, but a starter...

CPP / C++ / C Code:

while( input>>n )

This already reads the first number. By calling:

CPP / C++ / C Code:

input>>n;

You're reading the next number and ignoring the first.

By reading the number into n, you can do anything you want to do with them. Add it, subtract it, multiply it, divide it (though I don't suggest it with an int). It depends what you want to do your number read (n). When you're done with it, your loop automatically reads the next number.

cvirus · #3 10-Jun-2007, 12:28

CPP / C++ / C Code:

ifstream input("c:\\file_in.txt");

I want go to this .txt file and put the numbers that exit in it to a stack or array and then make calculations and send them to the output file.

davekw7x · #4 10-Jun-2007, 15:22

Quote:

Originally Posted by cvirus

I want go to this .txt file and put the numbers that exit in it to a stack or array and then make calculations and send them to the output file.

1. Read from input file: Your program does this, but, as dlp tried to point out, the program skips every other input value from the file.

2. Put the input numbers into an array: Declare an array and put each input value into the array. Start with array index = 0 and increment the index for every input value that you read.

3. Make calculations: OK. What array? What calculations? It's your program---do whatever you want.

4. Write results to output file. Your program writes to output file. I would suggest that for learning and debug purposes you might want to print results to the standard output also (cout <<)

For example, here I simply read each value, perform a calculation, and put the result into an output file. If you want to store the values in an array, you can use count as the array index.

CPP / C++ / C Code:

#include <iostream>
#include <fstream>

using namespace std;

int main()
{

    char *inname  = "test.txt";
    char *outname = "test.out";

    int invalue;
    int result;

    ifstream instream(inname);
    if (!instream) {
        cout << "Couldn't open " << inname << " for reading." << endl;
        return 0;
    }
    ofstream outstream(outname);
    if (!outstream) {
        cout << "Couldn't open " << outname << " for writing." << endl;
        return 0;
    }

    int count = 0;
    while (instream >> invalue) {
        ++count;
        cout << "Item number " << count
             << ": value = " << invalue << endl;
        result = invalue * invalue - 1;
        outstream << result << endl;
        if (!outstream) {
            cout << "There was a problem writing item number "
                 << count << " to " << outname << endl;
            return 0;
        }
    }
    instream.close();
    outstream.close();
    cout << "The total number of items = " << count << endl;
}

Input file "test.txt":

Code:

Result of program run (console output):

Code:

Item number 1: value = 1
Item number 2: value = 2
Item number 3: value = 3
Item number 4: value = 4
Item number 5: value = 5
Item number 6: value = 99
Item number 7: value = 98
Item number 8: value = 100
Item number 9: value = -12334465
The total number of items = 9

Output file "test.out" after the run:

Code:

0
3
8
15
24
9800
9603
9999
-1599689984

Regards,

Dave

cvirus · #5 11-Jun-2007, 09:47

CPP / C++ / C Code:

#include <cstdlib>
#include <iostream>
#include <fstream>
#include <iomanip>

using namespace std;

int n;

void input_output()
{   
    int count=0;
    ifstream input("c:\\file_in.txt");
    ofstream out("c:\\file_out.txt");
    while (input>>n)
    {
          count++;
    out<<"\n"<<n<<endl;
    cout<<"valor n"<<count<<": "<<n<<endl;
    }
    
    input.close();
    out.close();  
}

int main()
{
input_output(); 
      system("PAUSE");
}

Thank you davekw7x great explanation, but now i need to put this values into
a a stack or into an array, how do i do this operation?

davekw7x · #6 11-Jun-2007, 09:52

Quote:

Originally Posted by cvirus

now i need to put this values into
a a stack or into an array, how do i do this operation?

As I said before:

Quote:

Originally Posted by davekw7x

2. Put the input numbers into an array: Declare an array and put each input value into the array. Start with array index = 0 and increment the index for every input value that you read.

Regards,

Dave

cvirus · #7 11-Jun-2007, 12:44

I have read what you post, but i don´t know how to put those numbers into an array.

Thank you

davekw7x · #8 11-Jun-2007, 12:55

Quote:

Originally Posted by cvirus

but i don´t know how to put those numbers into an array.

Look for examples in your book or class notes.

This is how you declare an array:

CPP / C++ / C Code:

   int x[100]; /* an array of 100 ints */

This is how you store something in the array (note that the value of count must be greater than or equal to zero and less than or equal to 99 for the above declaration)

CPP / C++ / C Code:


int something;
int count;
.
.
.
.
    x[count] = something;
.
.
.

Regards,

Dave

cvirus · #9 14-Jun-2007, 11:24

CPP / C++ / C Code:

#include <cstdlib>
#include <iostream>
#include <fstream>
#include <iomanip>

using namespace std;

int n;

void input_output()
{   
    int count=0;
    int v[100];
    ifstream input("c:\\file_in.txt");
    ofstream out("c:\\file_out.txt");
    while (input>>n)
    {
          count++; 
    out<<"\n"<<n<<endl;
    cout<<"valor n"<<count<<": "<<n<<endl;
    v[count]=n;
    }
    input.close();
    out.close();  
}

int main()
{
input_output(); 
      system("PAUSE");
}

I made this way, but it´s not working. Is this you mean?

dlp · #10 14-Jun-2007, 12:12

what about it isn't working?

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Read from files

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