We know that a complex number has two parts real and imaginary. A complex number is written in form x+iy.
Real part is x and imaginary part is iy.
If imaginary part is 0, then we will have real number.
And if both real and imaginary part is 0, so number will be 0.
We can write any real number as complex number.
Example: We can write 2 as 2+0·i
Therefore, all real number is also a complex number.