Today we practice file I/O while introducing more useful functions in the C++ STL.

Sorting

Apart from vectors and arrays, we can also use sort on strings.

To sort a vector of int in descending order, use sort(v.begin(), v.end(), greater<int>()).

<algorithm>

• swap(a, b) swaps the contents of a and b
• count(s.begin(), s.end(), 'x') counts the number of occurrences of the character 'x' in the string s
• reverse(s.begin(), s.end()) reverses a sequence

<string>

Functions that check if a character is part of a category (returns a boolean):

• isalpha(c) - if c is a - z or A - Z
• islower(c) - if c is a - z
• isupper(c) - if c is A - Z
• isdigit(c) - if c is 0 - 9
• isalnum(c) - if c is a - z, A - Z or 0 - 9
• isspace(c) - if c is a space character (e.g. space, new line, tab)

Type conversion:

• to_string(n) - converts integer n to string
• stoi(s) - converts string s to int
• stoll(s) - converts string s to long long