How to Repeat Execution from Main function after an Iteration

Question

So I have a program which simplifies a Boolean Expression. What I'm trying to achieve is that at the end of simplification of the first Expression I'd want the user to choose whether he would want to simplify another Expression or just Exit the Console Application ( The programme ).

Here's the code for the Main function

int main(int argc, char *argv[]) {

/* allow command line calling with arguments -m -b X
where X is a number. order or -m and -b X does not
matter*/
cout << "\Designed By a Student For the Students :)\n";
char choice;
do
{
    cout << "\nEnter the number of variables to be Minimized\n";
    cin >> m;
    if (argc >= 2)
    {
        string arg = argv[1];
        if (arg.find("-m") != -1) {
            show_mid = true;
            if (argc >= 3) {
                arg = argv[2];
                if (arg.find("-b") != -1)
                    MIN_BIT = atoi(argv[3]);
            }
        }
        else if (arg.find("-h") != -1) {
            cout << "-b X\tminimum bits should be X.\n"
                << "-m  \tshow mid process computation.\n"
                << "-h  \tshow this.\n";
                                     return 0;


        }
        else {
            if (arg.find("-b") != -1 && argc >= 3)
                MIN_BIT = atoi(argv[2]);

            if (argc >= 4) {
                arg = argv[3];
                if (arg.find("-m") != -1)
                    show_mid = true;
            }
            else
            {
                cout << "Invalid argument\n"
                    << "-b X\tminimum bits should be X.\n"
                    << "-m  \tshow mid process computation.\n"
                    << "-h  \tshow this.\n";
                                            return 0;

            }
        }
    }

    getinput();
    init();
    cout << "Press 'y' to Reduce Another Expression or 'n' to Close this Application";
    cin >> choice;
} while (choice == 'y');
WINPAUSE;
return 0;

}

As you can see above i've used a do while Loop for the purpose, but i face two issues here i.e The programme terminates without taking user input and if I use WINPAUSE the programme exits when i PRESS ANY KEY. Is recursion an answer, please suggest a workaround.

Note: I use VS2017 IDE..:)

Edit: new code

int main(int argc, char *argv[]) {

/* allow command line calling with arguments -m -b X
where X is a number. order or -m and -b X does not
matter*/
cout << "\Designed By a Student For the Students :)\n";
char choice;
    if (argc >= 2)
    {
        string arg = argv[1];
        if (arg.find("-m") != -1) {
            show_mid = true;
            if (argc >= 3) {
                arg = argv[2];
                if (arg.find("-b") != -1)
                    MIN_BIT = atoi(argv[3]);
            }
        }
        else if (arg.find("-h") != -1) {
            cout << "-b X\tminimum bits should be X.\n"
                << "-m  \tshow mid process computation.\n"
                << "-h  \tshow this.\n";


        }
        else {
            if (arg.find("-b") != -1 && argc >= 3)
                MIN_BIT = atoi(argv[2]);

            if (argc >= 4) {
                arg = argv[3];
                if (arg.find("-m") != -1)
                    show_mid = true;
            }
            else
            {
                cout << "Invalid argument\n"
                    << "-b X\tminimum bits should be X.\n"
                    << "-m  \tshow mid process computation.\n"
                    << "-h  \tshow this.\n";

            }
        }
    }
    do
    {
        cout << "\nEnter the number of variables to be Minimized\n";
        cin >> m;
        getinput();
        init();
        cout << "Press 'y' to Reduce Another Expression or 'n' to Close this Application";
        cin >> choice;
    } while (choice == 'y');
WINPAUSE;
return 0;

}

edit : Here's the code for getinput() and init()

void getinput() {
unsigned in;
int num_bits = 0;
cout << "\nInput value followed by ENTER[^D ends input]\n> ";
while (cin >> in) {
    input_values.push_back(in);
    num_bits = count_bits(in);
    if (num_bits>MIN_BIT)
        MIN_BIT = num_bits;
    cout << "> ";
}
}
/*return min number of bits a number is represented by. used for best output*/
unsigned count_bits(unsigned n) {
    short bit = 0;
    int count = 0;
    while (n>0) {
        bit = n % 2;
        n >>= 1;
        count++;
    }
    return count;
}


void init() {
table.resize(1);
p_group.resize(1);
final_group.resize(1);
create_table();
print_table();
create_p_group();
if (show_mid)
    print_p_group();
create_final_group();
print_final_group();

}

Answer 1

You logic is flawed in a number of places, and though the pile of globals make it somewhat obfuscated, some things are clear:

• Stop reprocessing command line arguments on each iteration.
• Realize that formatted extraction of a char does NOT skip whitespace

The former of these is likely proper if you're properly parsing your command line arguments. In short, if you find your program terminating prior to reaching your loop, it means your command line arguments are either not proper, or your parsing logic is broken

The latter of these is what is holding up your loop from properly terminating. Your prior formatted input, unless consuming full line data (including the trailing newline), will leave at least a newline on the input stream. Without clearing that, the formatted character read for choice will simply use that, which obviously isn't the value 'y'. To accommodate for that, prior to reading the choice, discard any data in the input stream through any newline. Note: this step is NOT needed if your input processing is using something like std::getline, which consumes (and discards) newlines.

You loop should look like this:

int main(int argc, char *argv[])
{
    /* configure command line argument settings ONCE */
    if (argc >= 2)
    {
        string arg = argv[1];
        if (arg.find("-m") != -1) {
            show_mid = true;
            if (argc >= 3) {
                arg = argv[2];
                if (arg.find("-b") != -1)
                    MIN_BIT = atoi(argv[3]);
            }
        }
        else if (arg.find("-h") != -1) {
            cout << "-b X\tminimum bits should be X.\n"
            << "-m  \tshow mid process computation.\n"
            << "-h  \tshow this.\n";
            return 0;

        }
        else {
            if (arg.find("-b") != -1 && argc >= 3)
                MIN_BIT = atoi(argv[2]);

            if (argc >= 4) {
                arg = argv[3];
                if (arg.find("-m") != -1)
                    show_mid = true;
            }
            else
            {
                cout << "Invalid argument\n"
                << "-b X\tminimum bits should be X.\n"
                << "-m  \tshow mid process computation.\n"
                << "-h  \tshow this.\n";
                return 0;
            }
        }
    }

    cout << "Designed By a Student For the Students :)\n";
    char choice = 'y';
    do
    {
        cout << "\nEnter the number of variables to be Minimized\n";
        if (cin >> m)
        {
            getinput();
            init();
            cout << "Press 'y' to Reduce Another Expression or 'n' to Close this Application";

            // flush through eoln, read prompt
            std::cin.ignore(std::numeric_limits<std::streamsize>::max(), '\n');
            if (!(std::cin >> choice))
                break;
        }
        else
        {   // could not extract a valid value for m. not much more we can do.
            break;
        }

    } while (choice == 'y');
    return 0;
}

Answer 2

Move the part of checking the command line arguments before your for loop, like this:

cout << "\nEnter the number of variables to be Minimized\n";
cin >> m;
if (argc >= 2)
{
        string arg = argv[1];
        ...
        else
        {
            cout << "Invalid argument\n"
                << "-b X\tminimum bits should be X.\n"
                << "-m  \tshow mid process computation.\n"
                << "-h  \tshow this.\n";
            return 0;
        }
    }
}

do
{
    // your logic, init(), etc.
    cout << "Press 'y' to Reduce Another Expression or 'n' to Close this Application\n";
    cin >> choice;

} while (choice == 'y');

and then your

You have many statements of this kind:

if (arg.find("-m") != -1)

You should use string::npos to test for no matches found, as suggested in the std::string::find. So change them to, in this way:

if (arg.find("-m") != string::npos)

I'd have to make the main function void

NO.

Do not do that. What should main() return in C and C++? int is the answer.