[Hacktoberfest] more operators

[mayankgoyal-13]

Add more operators in calculator

[mayankgoyal-13]

Please assign this to me and also add hacktoberfest label

[mayankgoyal-13]

Made changes #34 #35

[Nivedita-coder]

Please assign this to me and also add hacktoberfest label

Okay, go ahead!

[kartikagarwal9]

Assign me

[Nivedita-coder]

Assign me

It's open for everyone.