[SOLVED]What is the error in this code ?

Question

https://code.sololearn.com/cf56q7gkFwle/?ref=app
This code is giving the desired result but generating a error at end . Why is that error generated ?
[SOLVED]

Answer 1

Vijay Gunwant

Change int a = 0 to long unsigned int a = 0

https://www.educba.com/unsigned-int-in-c/

Answer 2

not an error, a warning, because you compare two different number types (a is int and s.length() is long unsigned int)

Answer 3

🅰🅹 🅐🅝🅐🅝🅣 and visph thanks for your help