Question

C++

create a program that:

in main:

-opens the file provided for input (this file is titled 'Lab_HW10_Input.txt' and simply has 1-10, with each number on a new line for 10 lines total)

-calls a function to determine how many lines are in the file

-creates an array of the proper size

-calls a function to read the file and populate the array

-calls a function to write out the contents of the array in reverse order

*output file should be named 'reverse_output.txt'

Answer 1

Following is the required code and it's been written in Code::Blocks IDE:

The code BEGINS from here:

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

using namespace std;

// SIGNATURES of the required functions
int lines (ifstream&);
void populate (ifstream&, int []);
void rvrsArrWrite (ofstream&, int [], int);

// MAIN FUNCTION
int main()
{
int filesize;

// Opening file streams to input and output files
ifstream inputFile("Lab_HW10_Input.txt");
ofstream outputFile("reverse_output.txt");

// If input file is not found
if(inputFile == NULL){
cout << "File Does Not Exist!";
exit(0);
}

// call to function lines() and assigning the returned value to 'filesize'
filesize = lines(inputFile);
cout << "Number of lines in the file: " << filesize << endl;

// To make the pointer go back to the beginning of the file
inputFile.clear();
inputFile.seekg(0, ios::beg);

// creating an array of proper size
int arr[filesize];

// call to function populate()
populate(inputFile, arr);

// Elements in the array
cout << "Following are the elements in the array: " << endl;
for(int i = 0; i < filesize; i++){
cout << arr[i] << " ";
}

// call to the function rvrsArrWrite()
rvrsArrWrite(outputFile, arr, filesize);

// Closing the File Streams
inputFile.close();
outputFile.close();

cout << endl;
return 0;
}

// Function lines() - to determine the number of lines in the file
// @param ifstream& - a reference to the file input stream variable
int lines (ifstream &file){

string tname;
int len = 0; // stores the number of lines in the file
while (std::getline(file, tname)) {
len++;
}
return len;

}

// Function populate() - to read the file and populate the array
// @param ifstream& - a reference to the file instream variable
void populate(ifstream &file, int arr[]){

int temp; // to temporarily store the data from the file, for each line
int i = 0; //for indexing of array
while(file>>temp){
arr[i] = temp;
i++;
}
cout << "\nThe array has been populated Successfully!" << endl;

}

// Function rvrsArrWrite() - to write the contents of array to a file in reverse order
// @param ofstream& - a reference to the file outstream variable
// @param int [] - integer array to be reversed and written to file
// @param int - size of the array
void rvrsArrWrite(ofstream &file, int arr[], int length){

// Looping through each element in the array and writing it to the file
for(int i = length-1; i >= 0; i--){
file << arr[i] << endl;
}
cout << "\n\nWriting to the file named \"reverse_output\" is done Successfully!" << endl;
cout << "Please open the file in a text editor to check its contents..." << endl;

}

The code ENDS here!

Some KeyPoints about the program:

• The method used to count the number of lines in the file is very simple. First we declare an integer variable int the function lines(), named len, and set its value to 0. We go through each line in the file and increment the value of filesize by 1. And at the end of the function, we return the value of len.
• After this we assign the variable filesize with the returned value of len and use this variable filesize to declare an array of appropriate size with the statement as shown below:

int arr[ filesize ];

• One thing that would, perhaps, confuse you in the program is the use of the following statements:

inputFile.clear();
inputFile.seekg(0, ios::beg);

These statements are very necessary inn this program. Allow me to explain why? After using the funtion, lines(), we read the file and as the pointer finishes reading the last data in the file, it sets the eof (End of File). Then if we hadn't used the above statements and try to use the file again in populate() function, it would have read nothing, because the pointer is already at the end. So these two statements clear the eof flag and sends the pointer back to the starting of the file.

• the rvrsArrWrite() function reads each element of the array starting from the last (lenth-1)th and reaching the 0th element and writing each element to the file "reverse_output.txt" during the process.

Following is a ScreenShot of the sample data in the 'Lab_HW10_Input.txt' file:

This is the Screenshot of the Output for a Test Run for above input file:

And here is the ScreenShot of the "reverse_output.txt" file after the program executed:

Hope the code meets all your requirements.

Best Wishes!