C++ program assistance needed

Hello all,

I've got a question regarding a programming assignment that is due by midnight. The objective is to create a program that converts a binary number (up to 32 bits long) to decimal. The problems I have run up against thus far are:

1) Without the error checking for an entry being 1 or 0, I have a problem getting the original binary number to be displayed on the "____ in binary is ____ in decimal." line.
2) With error checking, it keeps automatically passing by the binary number entry line and saying that it is not a valid binary number.

Here is my current code:

Code:

---

#include <iostream>
#include <iomanip>
using namespace std;
int main()
{
  char entry[32];
  char decision, exit_option;
  int place = 0, digit, decimal = 0;
  int n = 0, power = 1;

  cout << "This program converts positive integer binary numbers"
      << " (up to 32 bits) into a decimal number.\n\n"
      << "Would you like to convert a binary number? (Y or y): ";
  cin >> decision;
  exit_option = 'Y';

  while((exit_option == 'Y')||(exit_option == 'y'))
  {
    if((decision == 'Y')||(decision == 'y'))
      {
      cout << "\n\nPlease enter your binary number:\n\n";
      cin >> entry[0];
      while (entry[place] != '\n')
        {
        place ++;
        cin >> noskipws >> entry[place];
        }
      if((entry[place] != 1)||(entry[place] != 0))
        {
        cout << "\n\nThis is not a binary number. Try again? ";
        cin >> exit_option;
        }
      else
        {
        for(digit = place-1; digit >= 0; digit --)
          {
          decimal += (entry[digit] - '0')*power;
          power *= 2;
          }
        cout << entry[place] << "in binary is " << decimal << " in decimal.\n\n";
        cout << "Continue? (Y or y): ";
        cin >> exit_option;
        }
      }
    else
      {
      cout << "Thanks anyway!";
      exit_option = 'n';
      }
  }
  cout << "\n\nThank you for using the Binary Number Convertor!\n\n";
  return 0;
}

---

Thanks for any help/advice given.

There's a difference between 1 (the number 1) and '1' (the character '1'). Since you're reading in characters, you should probably consider that entry[place] might be '1' or '0' rather than 1 or 0.

I re-introduced the single quotes around the 0 and 1 and the same result holds. It's something in the order/placement of the if, skipws/noskipws, or something.

Does it choke before the \n, or on the \n itself? (Notice that you read in the new-line character and then run the error check, before the while loop can stop you.)

After running the program, here's what happens:

First time through, it allows me to enter a binary number. After hitting enter, it comes up with the "This is not a binary number." line. When asked to continue and I input yes (y), it jumps back and again goes through to the "This is not a binary number." line without allowing me to enter a number.

Code:

---

This program converts positive integer binary numbers (up to 32 bits) into a decimal number.

Would you like to convert a binary number? (Y or y): y


Please enter your binary number:

101


This is not a binary number. Try again? y


Please enter your binary number:



This is not a binary number. Try again? y


Please enter your binary number:



This is not a binary number. Try again? y


Please enter your binary number:



This is not a binary number. Try again? n


Thank you for using the Binary Number Convertor!

---

The not-being-able-to-do-a-second-try is due to your not resetting place before re-reading. And I'm still guessing that nothing-being-a-binary-number is due to the mishandling of the \n.

Quote:

---

Originally Posted by tabstop

The not-being-able-to-do-a-second-try is due to your not resetting place before re-reading. And I'm still guessing that nothing-being-a-binary-number is due to the mishandling of the \n.

---

I'm not quite sure what you're getting at here then with the \n bit - d'you mean the while statement involving \n? That's the only place where it's used as a character. Would I need to move the error check of the "if" into the while statement? I'm confused.

Quote:

---

Originally Posted by Velocity

I'm not quite sure what you're getting at here then with the \n bit - d'you mean the while statement involving \n? That's the only place where it's used as a character. Would I need to move the error check of the "if" into the while statement? I'm confused.

---

Well, yes; at the moment the only character you ever check to see if it is a 1 or a 0 is the \n at the end, since the check only happens after you are done with the while loop.

All right, but when I do that the program goes insane. I just don't know where/when this error check should occur. When I don't have it in the program AT ALL, the program compiles and runs without much problem:

Code:

---

#include <iostream>
#include <iomanip>
using namespace std;
int main()
{
  char entry[32];
  char decision, exit_option;
  int place = 0, digit, decimal = 0;
  int n = 0, power = 1;

  cout << "This program converts positive integer binary numbers"
      << " (up to 32 bits) into a decimal number.\n\n"
      << "Would you like to convert a binary number? (Y or y): ";
  cin >> decision;
  exit_option = 'Y';

  while((exit_option == 'Y')||(exit_option == 'y'))
  {
    if((decision == 'Y')||(decision == 'y'))
      {
      cout << "\n\nPlease enter your binary number:\n\n";
      cin >> entry[0];
      while (entry[place] != '\n')
        {
        place ++;
        cin >> noskipws >> entry[place];
        }
      for(digit = place-1; digit >= 0; digit --)
        {
        decimal += (entry[digit] - '0')*power;
        power *= 2;
        }
      cout << entry[place] << "in binary is " << decimal << " in decimal.\n\n";
      cout << "Continue? (Y or y): ";
      cin >> exit_option;
      }
    else
      {
      cout << "Thanks anyway!";
      exit_option = 'n';
      }
  }
  cout << "\n\nThank you for using the Binary Number Convertor!\n\n";
  return 0;
}

---

The problem with THIS code is that it does not display the binary number at the end "____ in binary is ____ in decimal."

Never mind, it doesn't work without difficulty.

You need to print entry, not entry[place], as that will (still) only print the newline character and not the whole thing.

And you still need to set place back to 0 before trying to read in a second number.

I scrapped the one without error check -- after trying a 32-bit number it decided to display it as being -1 in decimal. :-/

This is beginning to frustrate... even after setting place back to 0 at the top of the while loop and taking out entry[place] (inserting entry instead, is that what you meant?) it does the same thing.

Quote:

---

Originally Posted by Velocity

I scrapped the one without error check -- after trying a 32-bit number it decided to display it as being -1 in decimal. :-/

---

You say that as though that is incorrect. However, 11111111111111111111111111111111 is -1. (Or, more specifically, how -1 is represented in most computers these days.)

Quote:

---

Originally Posted by Velocity

This is beginning to frustrate... even after setting place back to 0 at the top of the while loop and taking out entry[place] (inserting entry instead, is that what you meant?) it does the same thing.

---

You'll have to show me what you mean.

Quote:

---

Originally Posted by tabstop

You say that as though that is incorrect. However, 11111111111111111111111111111111 is -1. (Or, more specifically, how -1 is represented in most computers these days.)

---

...I knew that.

<_<
>_>

Quote:

---

You'll have to show me what you mean.

---

Where "entry[place]" was in the original code, I replaced with just "entry". I don't think that's right though.

The second bit of code (the one without the error check) runs the first time correctly, then upon re-entrance into the loop it goes nuts again and displays the same number over again. Code is below...

Code:

---

#include <iostream>
#include <iomanip>
using namespace std;
int main()
{
  char entry[32];
  char decision, exit_option;
  int place = 0, digit, decimal = 0;
  int n = 0, power = 1;

  cout << "This program converts positive integer binary numbers"
      << " (up to 32 bits) into a decimal number.\n\n"
      << "Would you like to convert a binary number? (Y or y): ";
  cin >> decision;
  exit_option = 'Y';

  while((exit_option == 'Y')||(exit_option == 'y'))
  {
    if((decision == 'Y')||(decision == 'y'))
      {
      place = 0;
      cout << "\n\nPlease enter your binary number:\n\n";
      cin >> entry[0];
      while (entry[place] != '\n')
        {
        place ++;
        cin >> noskipws >> entry[place];
        }
      for(digit = place-1; digit >= 0; digit --)
        {
        decimal += (entry[digit] - '0')*power;
        power *= 2;
        }
      cout << entry << "in binary is " << decimal << " in decimal.\n\n";
      cout << "Continue? (Y or y): ";
      cin >> exit_option;
      }
    else
      {
      cout << "Thanks anyway!";
      exit_option = 'n';
      }
  }
  cout << "\n\nThank you for using the Binary Number Convertor!\n\n";
  return 0;
}

---

cin >> exit_option leaves a \n in the input buffer, which is cheerfully read into input[0] at the top of the next loop. Adding "cin.ignore()" directly after this works wonders. (Edit: I mean directly after cin>>exit_option.)

Next, you will discover that power isn't reset, and that maybe you want to reset your input array too.

All right, good to know - now the problem is that when it displays the binary-decimal line, it still displays the \n line so that the binary number is one line above the rest... e.g.:

Please enter your binary number:

101
101
in binary is 5 in decimal.

You know where the \n is in your array -- it's at array[place]. So set array[place] to \0 and be done with it.

Okay thanks. Now the only thing left, I think, is putting in the error check for it being 1 or 0. Now, we already said that it has to be implemented into the while loop... but the last time I did that, the program went insane.

Since you can't really get characters one at a time anyway, the idea of checking things as they are read in is not perhaps as real-time as you were hoping. But anyway, you should put it in there, and if it fails set a flag. Then outside the loop either print the sorry message, or do the conversion, depending on the flag.

Okay, so I would have to do something like this?

Code:

---

...

while((exit_option == 'Y')||(exit_option == 'y'))
  {
    if((decision == 'Y')||(decision == 'y'))
      {
      place = 0;
      power = 1;
      cout << "\n\nPlease enter your binary number:\n\n";
      cin >> entry[0];
      while (entry[place] != '\n')
        {
        place ++;
        cin >> noskipws >> entry[place];
        [[ERROR CHECK HERE]]
        }                                             
      for(digit = place-1; digit >= 0; digit --)
        {
        decimal += (entry[digit] - '0')*power;
        power *= 2;
        }
      entry[place] = '\0';
      cout << "\n\n" << entry << " in binary is " << decimal << " in decimal.\n\n";
      cout << "Continue? (Y or y): ";
      cin >> exit_option;
      cin.ignore();
      }
    else
      {
      cout << "Thanks anyway!";
      exit_option = 'n';
      }
  }

...

---

The check there, yes. And then you wouldn't do the conversion if the check didn't succeed.

I know that would involve a break somewhere in the loop, but I'm not sure how to go from there...?

Code:

---

...

      while (entry[place] != '\n')
        {
        place ++;
        cin >> noskipws >> entry[place];
        if((entry[place] != '1')||(entry[place] != '0'))
          break;
        }
      for(digit = place-1; digit >= 0; digit --)
        {
        decimal += (entry[digit] - '0')*power;
        power *= 2;
        }
      entry[place] = '\0';
      cout << "\n\n" << entry << " in binary is " << decimal << " in decimal.\n\n";
      cout << "Continue? (Y or y): ";
      cin >> exit_option;
      cin.ignore();
      }

...

---

Breaking the loop would be A Very Bad Thing Indeed, since the rest of the input would not be processed and would interfere with future execution. Just set a flag, and if the flag is set when you get out don't do the conversion.

I'm not quite sure what you mean by a flag in this sense. I've got the if expression there, and I'm assuming I'll have to use "else" to get the conversion actually done (enclosing the "for" section inside an "else"). So with the "if" being "if it's neither 1 nor 0," then it's there I have to input the "try again?" question, right?

Quote:

---

Originally Posted by Velocity

I'm not quite sure what you mean by a flag in this sense. I've got the if expression there, and I'm assuming I'll have to use "else" to get the conversion actually done (enclosing the "for" section inside an "else"). So with the "if" being "if it's neither 1 nor 0," then it's there I have to input the "try again?" question, right?

---

Absolutely not. You must process (or at least .ignore) all the input that was typed in -- otherwise when you ask if they want to go again, your program will say the answer is "100101". And you can't do the for until after the while loop is finished anyway; so you can't ask the question until you have all the input in the first place.

Okay, what you're saying makes sense. My only problem now is just where does the "if" statement actually go. You said it has to go within the while loop, but now it's to where I have to let all the data be input. You mention cin.ignore() again... here's a snippet, am I on the right track or is what you're saying going completely over my head?

Code:

---

...
      while (entry[place] != '\n')
        {
        place ++;
        cin >> noskipws >> entry[place];
        if((entry[place] != '1')||(entry[place] != '0'))
          {   
          cin.ignore();
          cout << "This is not a valid binary number. Try again? (Y or y) "
          cin >> exit_option;
          }
        }
      for(digit = place-1; digit >= 0; digit --)
        {
        decimal += (entry[digit] - '0')*power;
        power *= 2;
        }
...

---

This is what it should look like:

Code:

---

      bool is_binary = true;
      cin >> entry[0];
      while (entry[place] != '\n')
        {
        if (entry[place] != '0' && entry[place] != '1') is_binary=false;
        place ++;
        cin >> noskipws >> entry[place];
        }         
      if (is_binary) {
        //convert
      } else {
        //print sorry
      }
      //print prompt

---

Ohh, the check goes BEFORE the input...

Quote:

---

Originally Posted by Velocity

Ohh, the check goes BEFORE the input...

---

Well, you have to check the first one (input[0]) before you read the next one. Also, this prevents the "checking \n problem" we had before.

Yeah that would make sense, wouldn't it... haha. Man, don't know how I missed that. Since it prevents the \n thing does this mean that the cin.ignore is unnecessary toward the end now or should I keep it in there for a safeguard?

The cin.ignore doesn't ignore this new-line (this new-line gets read in in your loop); it ignores the one after "Another?"

It finally works. Thanks a TON for your help, tabstop, I really appreciate it.