Why is islower function always showing 0 no matter what character I use?

Question

In documentation, they specified dat if islower accepts a lowercase character, the output number should be more than 0 which is not the case with the program attached to it.
https://code.sololearn.com/c617AzNt8975/?ref=app

Answer 1

Give single quotes to the char like t='p'.

Answer 2

In C, 'p' and "p" both are different. Double quotes represent array which ends with a null character.

Answer 3

Thank you so much

Answer 4

Thanks, it worked. But what's the intuition behind it??