How to Ensure a C++ Program Reads Exactly 52 Mappings from a File?

[lee_sarah76]

Homework Statement

This program must read two input files, one is a key that specifies the conversion of characters
the other is a text message that will be encoded based on the mapping specified in the key
files. The program must use the key mappings to both encode and decode the message file.
The user can choose between two options, encoding and decoding.
When encoding the encoded file name must bethe same as the input message plus a ".enc" extension.
When decoding the decoded file name must be the same as the input message plus a ".dec" extension.

Above is the whole Problem Statement. However, my specific problem is that after the file that is being read is inputting values into two given vectors, I need to make sure that the file contained 52 by 2 elements or else the program must exit.

Homework Equations

N/A

The Attempt at a Solution

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

int main()
{

    /*
     Three file names are needed.
     One will contain the key that specifies the character mappings.
     One will hold the name for the message.
     One will hold the name for the encoded message.
     The string 'extension'.
    */
    
    std::string keyFileName, messageFileName, encodedMessageFileName, extension;
    
    std::ifstream keyFile;
    std::ifstream messageFile;
    std::ofstream encodedMessageFile;
    
    char choice = 'E';
    do
    {
        std::cout << "\nWhat would you like to do? Encode/Decode?";
        std::cout << "\nPlease key in 'E' or 'D': ";
        std::cin >> choice;
    } while( choice != 'E' && choice != 'D');
    
    do
    {
        std::cout << "\nKey in a valid key file name: ";
        std::cin >> keyFileName;
        
        keyFile.open(keyFileName.c_str());
        if( !keyFile.is_open())
        {
            std::cout <<"\nFailed to open." << keyFileName;
        }
    }while (! keyFile.good() );
    
    
    do
    {
        std::cout << "\nKey in a message name: ";
        std::cin >> messageFileName;
        
        messageFile.open(messageFileName.c_str());
        if( !messageFile.is_open())
        {
            std::cout <<"\nFailed to open." << messageFileName;
        }
    }while (! messageFile.good() );
    
    if(choice == 'E')
    {
        extension = ".enc";
    }
    else
    {
        extension = ".dec";
    }
    //The two strings are now concatenated.
    encodedMessageFileName = messageFileName + extension;
    
    
    char from[52];
    char to[52];
    
    
    if(choice == 'E')
    {
        for(int i = 0; i < 52; i++)
        {
            keyFile >> from[i];
            keyFile >> to[i];
            
            {
                //[B]In here is where the loop should go, and I'm also fairly positive it should be the eof //function that I am calling but I'm not sure how to go about that exactly. [/B]
                
                
                exit(1);
            }
        }
    }
    else
   {
        for(int i = 0; i < 52; i++)
        {
            keyFile >> to[i];
            keyFile >> from[i];
            
           {
                //[B]In here is where the loop should go, and I'm also fairly positive it should be the eof //function that I am calling but I'm not sure how to go about that exactly. [/B]
                
                
                exit(1);
            }
       }
   }

keyFile.close();
[B]And here is where the 1-1 mapping goes I believe and I think it should be a for loop but I'm not exactly sure how to do that either. [/B]
}

I'm not looking for someone to give me the answers, but if someone could point me in the right direction that would be splendid!

 

[KataKoniK]

Thank you!

Hello,

It seems like you have made good progress on your program so far. To address your specific problem, you can use the "eof" function to check if the file has reached the end. This function returns true if the end of the file has been reached and false if it has not. You can use this in a while loop to continue reading from the file until the end is reached.

For example:

while(!keyFile.eof()) {
//read from file
}

This way, your loop will continue until the end of the file is reached. You can also use this in conjunction with a counter variable to keep track of the number of elements read from the file and exit the program if it is not equal to 52.

I hope this helps and good luck with your program!