Thread: Hey guys, back again with a question

All right, so this time I have an assignment to add two positive integers up to 20 digits long and output the two entries along with the sum. To this point I've been able to get the program to compile but the output is out of whack. Here's what I've got, and an example of the output:

Code:

#include <iostream>
using namespace std;
int main()
{
  char augend[20] = {0}, addend[20] = {0}, sum[21], temp[20];
  int aug = 0, add = 0, sumc = 20, tempc = 0;
  int carry = 1;

  cout << "This program adds two positive integers up to 20 digits long."
       << "\n\n";
  cout << "Enter the augend: ";
  cin >> noskipws >> temp[0];
  while(temp[tempc]!='\n')
    {
      tempc++;
      cin >> temp[tempc];
    }
  cout << "Enter the addend: ";
  cin >> noskipws >> addend[0];
  while(addend[add]!='\n')
    {
      add++;
      cin >> addend[add];
    }
  for(aug=tempc; aug>=0; aug--, tempc--)
    {
      augend[aug] = temp[tempc];
    }
  for(aug=19, sumc=20; aug>=0, sumc>=0, add>=0; aug--, sumc--, add--)
    {
      if(augend[aug] + addend[add] >= 10)
        {
          sum[sumc] = augend[aug] + addend[add] - 10;
          sum[sumc - 1] = carry;
        }
      else
        {
          sum[sumc] = augend[aug] + addend[add];
        }
    }
  temp[tempc]='\0';
  addend[add]='\0';
  cout << "\n\n" << temp << "+" << addend << "=" << sum << ".\n";
  return 0;
}

And a sample output:

Code:

This program adds two positive integers up to 20 digits long.

Enter the augend: 2021
Enter the addend: 395


2021
+395
= R@.

All right, what's screwy here? I have a feeling part of it is due to the addition of the two arrays (augend and addend) - I'm not confident I've done that right. Advice/assistance?

Could you say step by step what you are trying to do?

I really don't understand what your trying to do.

Sure... at this point in my class (well, for this homework assignment, really), it's an emphasis on arrays. What the assignment is asking is for us to do the following...

1) Read in up to a 20-digit positive integer into the "temp" (first number) array.
2) Read in up to a 20-digit positive integer into the "addend" (second number) array.
3) Shift the "temp" array into an "augend" array which allows for easier addition. If it's a three digit number, then it's akin to taking the 0, 1, 2 places of the "temp" array and putting them into the 17, 18, 19 places (respectively) of the "augend" array.
4) Add the individual digits of the "augend" and "addend" arrays place by place (i.e., augend[19]+addend[19]) and putting them into a "sum" array.
5) Display the augend and addend arrays in the output with the sum array.

Example:

temp[] is read in as 2345. addend[] is read in as 678.
temp[0] = 2, temp[1] = 3, temp[2] = 4, temp[3] = 5. Once the shift is done, it would be: augend[16] = 2, augend[17] = 3, augend[18] = 4, augend[19] = 5.

Then add the "augend" and "addend" arrays. So it would be...

augend[19] + addend[2] = sum[20]
augend[18] + addend[1] = sum[19]
augend[17] + addend[0] = sum[18]
augend[16] = sum[17]

Of course another wrinkle is the use of "carry" to aid in carrying over the 1 that comes from things like 8+5 and 7+4.

And what is the error your getting?

Well, look at the sample output above. I put in 2021 and 395 ... and the result is R@?

1) You have wrong initialization. This just makes the first char to 0. You want everything in the array to 0. Actually you want everything in the array to '0' not 0!
2) Shouldn't it be augend[aug] + addend[add] >= '10' //'10' not 10 ?
3) Shouldn't it be sum[sumc] += augend[aug] + addend[add] - 10; // += not = since you might have a carry ?
4) Shouldn't you initialize sum to '0'?

Well I've made a few changes and still am getting an error upon output. Here's the current code along with a sample output.

Code:

#include <iostream>
using namespace std;
int main()
{
  char augend[20] = {'0'}, addend[20] = {'0'}, sum[21] = {'0'}, temp[20];
  int aug = 0, add = 0, sumc = 20, tempc = 0;
  int carry = 1;

  cout << "This program adds two positive integers up to 20 digits long."
       << "\n\n";
  cout << "Enter the augend: ";
  cin >> noskipws >> temp[0];
  while(temp[tempc]!='\n')
    {
      tempc++;
      cin >> temp[tempc];
    }
  cout << "Enter the addend: ";
  cin >> noskipws >> addend[0];
  while(addend[add]!='\n')
    {
      add++;
      cin >> addend[add];
    }
  for(aug=19; tempc>=0; aug--, tempc--)
    {
      augend[aug] = temp[tempc];
    }
  for(aug=19, sumc=20; aug>=0, add>=0; aug--, sumc--, add--)
    {
      if(augend[aug] + addend[add] >= '10')
        {
          sum[sumc] += augend[aug] + addend[add] - 10;
          sum[sumc - 1] = carry;
        }
      else
        {
          sum[sumc] += augend[aug] + addend[add];
        }
    }
  cout << "\n\n" << temp << " + " << addend << " = " << sum << ".\n";
  return 0;
}

Code:

This program adds two positive integers up to 20 digits long.

Enter the augend: 1234
Enter the addend: 3456


1234
 + 3456
 = 0.

Does anybody else have advice on this? I would like to do the assignment with arrays to really get the concept of it down but at this point I'm considering just scrapping it and using strings (which we haven't done yet) since the assignment is due tonight at midnight. The output is still the part that's making me scratch my head -- for one, the returns are still in the character arrays and, of course, the sum is being given out as 0 no matter what numbers I input.

aug>=0, add>=0

You can't use commas in the second part of a for-loop. (Well, you can, obviously, but it's not going to be what you expect -- the first part will be completely ignored. Use || if you want or, or && if you want and.)

Dino, I was just glad to see something syntactical that I didn't need to actually parse. And Velocity, you shouldn't have needed me to tell you that, since your compiler has been complaining about it the whole time:

Code:

temp.cpp:31:39: warning: multi-character character constant
temp.cpp: In function ‘int main()’:
temp.cpp:29: warning: left-hand operand of comma has no effect

And yes '10' is amazingly wrong. If you add '1' to '9' you'll get 'j'. You need to, when you see '1', actually use the value 1, not the value 49.