Should be the last time I bother everyone.

I'm trying to use the command line prompt to perform four operations. Encrypt a .txt file, decrypt a .txt file, output the first five lines on the screen, output the last five lines on the screen. I can encrypt and decrypt the file but I can't get the first five lines to print. Any help?

Code:

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#include <iostream>
#include <fstream>
#include <string>
using namespace std;
const int htlen=5;
const int ascLEn=256;
const int ecryptCode=10;
void print_usage()
{
      cout<<"Usage"<<endl;
      cout<<"      lab12 -e file1 file2  Encrypt file1 and write cyphertext to file2"<<endl;
      cout<<"      lab12 -d file1 file2  Decrypt file1 and write paintext to file 2"<<endl;
      exit(1);
}
int main(int argc, char* argv[])
{
      if (argc != 4)
            print_usage();
            if (strcmp(argv[1], "-e") !=0&&strcmp(argv[1], "-d")!=0)
                  print_usage();
      ifstream inData;
      ofstream outData;
      inData.open(argv[2]);
      outData.open(argv[3]);
      if (inData.fail()||outData.fail())
      {
            cout<<"File open error!"<<endl;
            return 1;
      }
      string s;
      if (strcmp(argv[1], "-e")==0)
      {
            while (!inData.eof())
            {
                  getline(inData, s);
                  for (int i=0;i<s.length();i++)
                        s[i]=char(s[i] + ecryptCode)%ascLEn;
                  outData<<s;
                  if (!inData.eof())
                        outData<<endl;
            }
      }
      else
      {
            while (!inData.eof())
            {
                  getline(inData, s);
                        for (int i=0;i<s.length();i++)
                              s[i]=char(s[i]+ascLEn-ecryptCode)%ascLEn;
                  outData<<s;
                  if (!inData.eof())
                        outData<<endl;
            }
      }
      inData.close();
      outData.close();
      return 0;
      system("pause");
}

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Have you tried outputting the string 's' to the screen using std::cout?

Code:

---

...
            int line = 0;
            while (!inData.eof())
            {
              ...
              if (line++ < 5)
              {
                std::cout << s << std::endl;
              }
            }

---

P.S. If your string data contains unprintable characters, then iterate over the length of the string, outputting each character. You might find it easier to read these character if they are outputted in hex. Something like:

Code:

---

...
for (size_t i = 0; i < s.size(); ++i)
{
  std::cout << std::setw(2) << std::setfill('0') << std::hex << (int) s[i] << std::dec << ' ';
}
std::cout << std::endl;

---

Here is what I'm trying now, but I'm still not getting any output. I'm sure it's something obvious but I can't see it. Even if I use the -h switch in the command prompt I still get no output.

Code:

---

#include <iostream>
#include <fstream>
#include <string>
using namespace std;
const int htlen=5;
const int ascLEn=256;
const int ecryptCode=10;
void print_usage()
{
        cout<<"Usage"<<endl;
        cout<<"      lab12 -e file1 file2  Encrypt file1 and write cyphertext to file2"<<endl;
        cout<<"      lab12 -d file1 file2  Decrypt file1 and write paintext to file 2"<<endl;
        exit(1);
}
int main(int argc, char* argv[])
{
        if (argc != 4)
                print_usage();
                if (strcmp(argv[1], "-e") !=0&&strcmp(argv[1], "-d")!=0)
                        print_usage();
        ifstream inData;
        ofstream outData;
        inData.open(argv[2]);
        outData.open(argv[3]);
        if (inData.fail()||outData.fail())
        {
                cout<<"File open error!"<<endl;
                return 1;
        }
        string s;
        if (strcmp(argv[1], "-e")==0)
        {
                while (!inData.eof())
                {
                        getline(inData, s);
                        for (int i=0;i<s.length();i++)
                                s[i]=char(s[i] + ecryptCode)%ascLEn;
                        outData<<s;
                        if (!inData.eof())
                                outData<<endl;
                }
        }
        else if (strcmp(argv[1], "-d")==0)
        {
                while (!inData.eof())
                {
                        getline(inData, s);
                                for (int i=0;i<s.length();i++)
                                        s[i]=char(s[i]+ascLEn-ecryptCode)%ascLEn;
                        outData<<s;
                        if (!inData.eof())
                                outData<<endl;
                }
        }
        else if (argv[1], "-h")
        {
                int line = 0;
            while (!inData.eof())
            {
              if (line++ < 5)
              {
                std::cout << s << std::endl;
              }
                        }

        }
       
        inData.close();
        outData.close();
        return 0;
        system("pause");
}

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Would it not be helpful to have one of these statements inside that new while-loop you added:

Code:

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getline(inData, s);

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