1's Complement
In Digital Electronics to find 1's complement is very very easy. It is nothing but changing the binary number. If it is 0 then will write it as 1 and if it is 1 then we will write it as 0.
For An Example:
The given number is 10101010
So, therefore, the 1's complement of that number will be 01010101.
As you guys can see that it is nothing but just changing the number between 0 and 1. It is as simple as that.