Addition of numbers in array as string

I am following these lines of code, but generating error when I do:

x = randi([0,9],1,20);
y = randi([0,9],1,20);
x_new = str2double(sprintf('%d',x));
y_new = str2double(sprintf('%d',y));
result = num2str(x_new+y_new) - '0';
fprintf('%4d',x);
fprintf('\n');
fprintf('%4d',y);
fprintf('\n');
disp('+');
disp('-------------------------------------------------------------------------')
fprintf('%d',result);
fprintf('\n')

The ouput I get (which is wrong):

   9   6   1   3   0   5   4   9   8   4   8   1   3   9   9   7   6   3   9   1
   7   6   8   3   7   8   3   5   9   5   3   6   3   7   4   4   6   9   3   8
+
-------------------------------------------------------------------------
1-272968385801777453-520

can someone please mention the mistake in running these lines. And help me to align (with same gap spaces) the result

the will be the addition of these numbers.

Thanks

Answer 1

[Walter Roberson]

double('1')

ans = 49

double('2')

ans = 50

'1' + '2'

ans = 99

char(ans)

ans = 'c'

MATLAB makes absolutely no attempt to recognize that if you add '1' + '2' that you might be wanting it to mean add 1 and 2.

char(('1' + '2') - '0')

ans = '3'

That works, but that isn't what you did.

num2str('1' + '2') - '0'

ans = 1×2

9 9

That's what you did. You got the printable representation of the sum and subtracted '0' from that, whereas what you needed was to subtract '0' from the sum.

But even then...

'3' + '8' - '0'

ans = 59

char(ans)

ans = ';'

When you do arithmetic on characters, you have to allow for overflow.

I suggest you subtract '0' from each of the characters, line the two up so that the right side matches and zero-pad on the left if need be. Now add, getting a vector of decimal values. Now run through the vector starting from the right, and each position that is 10 or greater, subtract 10 from that entry and add 1 to the entry to the left... watching out for a final carry that expanded the number of digits.

Once you have the vector of decimal values, having carried out the carries, add back '0' and convert to char()

[Muhammad Usman]

Can you please modify my code as my code works so fine when a choose:

x = randi([0,9],1,15);
y = randi([0,9],1,15);

the output is correct:

   1   9   5   4   9   6   4   8   5   5   6   3   2   5   8
   4   1   4   3   4   8   4   3   3   1   2   0   4   2   2
+
-------------------------------------------------------------------------
  6  0  9  8  4  4  9  1  8  6  8  3  6  8  0

[Walter Roberson]

fprintf('%4d',result);

[Muhammad Usman]

for 15 random number it works fine but when it do 20, it produce incrorect result.

[Rik]

How did you modify your code to account for the carry operation? So with the inputs '3' and '8', how are you making sure the result is '11'?

[Muhammad Usman]

it is working so fine for digits less than 16

like

   8
   3
+
-------------------------------------------------------------------------
   1   1

Please run the above code to make it possible to add number of 20 digits.

[Rik]

Your problem is that you didn't define the addition yourself, but didn't make sure to have an integer conversion either.

x = randi([0,9],1,30);
y = randi([0,9],1,30);
x_new = str2double(sprintf('%d',x));
y_new = str2double(sprintf('%d',y));
result = num2str(x_new+y_new)

result = '6.912464714624284e+29'

As you can see, num2str reverts to an exponential notation, so you will have to switch to something else:

result = sprintf('%.0f',x_new+y_new)

result = '691246471462428404899037315072'

[Walter Roberson]

Can you please modify my code as my code works so fine when a choose:

I already described what to do. You should revise your code nearly completely. I will not write this code for you, as you are doing a homework assignment.

I suggest you subtract '0' from each of the characters, line the two up so that the right side matches and zero-pad on the left if need be. Now add, getting a vector of decimal values. Now run through the vector starting from the right, and each position that is 10 or greater, subtract 10 from that entry and add 1 to the entry to the left... watching out for a final carry that expanded the number of digits.

Once you have the vector of decimal values, having carried out the carries, add back '0' and convert to char()