Add two big number using string in C programming

How to Add two big numbers using string

It's easy to add two numbers in any programming language. For example, if int a = 2; int b = 3, then we just add a + b. Now, if we try to add two numbers, each having 100 digits like 10000000000000000000000000000000000...., what should we do?

There is no data type to hold 100 digits in a variable. So, what can we do? The process is to take input as a string. Then we can add those numbers.
For example:

1234...

1234...

______

2568...

We add from the last string and store the sum in an array. Then just print them from the last element of the array.

Have a look:

char str1 [ ] = "1234..." ;

char str2 [ ] = "1234..." ;

Then, str1 [3] + str2 [3] = '4' + '4' = 104

Oops, what happened? It must be 8. OK, not to worry, here the sum is an ASCII value. So, we must subtract 0 from the string.

So, (str1 [3] - '0' ) + (str2 [3] - '0') = 4 + 4 = 8;

What happened here?

It's simple, in our string, str1 [3] = 4, which is a character, and its ASCII value is 52. If we subtract character 0 containing ASCII code 48. Then we get 52 - 48 = 4.
After doing this, we will store all the sums in an int-type array. Then we just print them from the last position of the array.

Now we got another problem. What happens when we add 129 + 124?
the last digit 9+4 = 13. In this case, we can use a carry and add the carrying value to the next addition. At first, carry is set to 0, and if the sum > 9, carry becomes 1; otherwise, it remains 0.
[Note:  try to solve yourself, following the algorithm above. If failed, then see the code]

Code for adding two big number

Happy Coding...