toLower(string s)

This function takes any string (like a movie title) and returns a version of it where every character is lowercase. This is important because C++ string comparison (using ==, <, or >) is case-sensitive by default. For example:

• "Inception" and "inception" would not be equal

• "The Dark Knight" would not match "the dark knight"

To fix this, we create a lowercase version of each string so that comparisons later in the program are fair and consistent. We do not change the original title stored in memory — we only use the lowercase version for comparing or sorting.