Question

Objectives:

• Practice using files and strings.
• More practice using loops with files and strings

Background

Assume you're working on a contract where the company is building a e-mailing list. Your task is to write a C++ program that reads through an e-mail stored in the current working directory, called mail.dat, and outputs every email address found as individual lines to a file called email_list.dat. For this assignment, if a whitespace delimited string of characters has an embedded commercial at sign (@) inside it (that is, anywhere in the string), we shall consider it an e-mail address. (Yes, this is somewhat simplistic, but this is more about practice even though this allows an email to have an @ sign at the beginning/end of an address which would not be allowed in the "real world".) However, you will need to trim any trailing commas. Thus the string "[email protected]," must appear in the output file as "[email protected]" with the trailing comma removed. Only commas at the end of a string are considered trailing; do not remove non-trailing commas. Do not worry about any other punctuation characters; the only editing your program must do is to remove trailing commas.

Answer 1

C++ Program :

#include <iostream>
#include <fstream> 
using namespace std;

int main()
{
    string str;
    int n;

    ifstream in("mail.dat");   // opens input file
    ofstream out("email_list.dat"); // writes to output file

    while(in>>str)    // read the strings in file until end of file
    {
        n = str.length();  // length of word or string
        for(int i=0; i<n; i++)
        {
            if(str[i] == '@') // search for @ in a string in the input file
            {
                if(str[n-1] == ',') // if  a trailing comma is found then this will ommit it
                {
                    n=n-1; // trim the string by 1 character
                }
                for(int j =0; j<n; j++)
                {
                    out<<str[j]; // print the whole string which is email-address to output file
                }
                out<<"\n"; // print a next line in output file
            }
        }
    }
    return 0;
}

Screenshots and Outputs :

Code :

Input file :

mail.dat

Output file :

email_list.dat