string str : is a fixed, read-only string stored in memory. You cannot modify it. so it is more correct and safer to be (const) char[]

pretty smart actually.

no, it is not valid ,as you said it access elements out of range array[-1] array[size]

plz can u explain why u wrote it like that?
like how it came to u to think about it

because you have using namespace std;, the compiler thinks islower is referring to the one in <locale>, not the one in <cctype>. either remove the using, or disambiguate the function reference with the :: operator: ::islower.

yuh

but the return value will be retuned as an integer. it won't convert to a char. that's not what you want the function to do

Please use spoiler flag next time, your post was visible in the homepage.

only to see what the output will look like

It's lambda-function, which finds out is number even (return true) or not (return false).

The bullets must be made of silver, and the dragons are allergic to silver, that's why they hoard gold!

Yeah