C++ STL

<algorithm>
std::sort
std::reverse
std::swap
std::move
std::count_if
std::min
std::max
std::min_element
std::max_element
std::accumulate

<numeric>
std::iota

<string>
std::to_string

<bitset>
std::bitset

Convert case in C / C++

C
 <ctype.h>
tolower
int tolower( int ch );
toupper
int toupper( int ch );

C++
<cctype>

std::tolower
int tolower( int ch );
std::toupper
int toupper( int ch );

SQL notes

SQL Tutorial:
https://www.w3schools.com/sql/default.asp

Bitwise operations in C

& bitwise AND
| bitwise inclusive OR
^ bitwise XOR (eXclusive OR)
<< left shift
>> right shift
~ bitwise NOT (one's complement) (unary)

Masking operation:
To get the k-th bit of number n,
(n & ( 1 << k )) >> k
or
int mask =  1 << k;
int masked_n = n & mask;
int thebit = masked_n >> k;

Swap two variables without a temporary variable:
int x = 10, y = 5;
Method 1. XOR
// Code to swap 'x' (1010) and 'y' (0101)
x = x ^ y; // x now becomes 15 (1111)
y = x ^ y; // y becomes 10 (1010)
x = x ^ y; // x becomes 5 (0101)

note: XOR is both commutative and associative

y = (x^y)^y = x^(y^y) = x^0 = x

x = (x^y)^(x^y)^y = x^y^x = y

Method 2. arithmetic // may cause overflow
// Code to swap 'x' and 'y'
x = x + y; // x now becomes 15
y = x - y; // y becomes 10
x = x - y; // x becomes 5