if statements with reverse

secret_handshake.h

#if !defined(SECRET_HANDSHAKE_H)
#define SECRET_HANDSHAKE_H
#include <vector>
#include <string>

namespace secret_handshake {
    std::vector<std::string> commands (unsigned int signal);
}  // namespace secret_handshake

#endif // SECRET_HANDSHAKE_H

secret_handshake.cpp

#include "secret_handshake.h"
#include <algorithm>

namespace secret_handshake {

std::vector<std::string> commands(unsigned int signal)
{
    std::vector<std::string> result;
    if (signal & 0b00001) result.emplace_back("wink");
    if (signal & 0b00010) result.emplace_back("double blink");
    if (signal & 0b00100) result.emplace_back("close your eyes");
    if (signal & 0b01000) result.emplace_back("jump");
    if (signal & 0b10000) std::reverse(begin(result), end(result));
    return result;
}
}  // namespace secret_handshake

The commands function starts by defining the vector to hold the returned actions.

It then has a series of if statements, each of which uses the bitwise AND operator to check if the input signal contains a particular action. Each action is represented by a binary literal, but could just as well be represented by its decimal value

    if (signal & 1)  result.emplace_back("wink");
    if (signal & 2)  result.emplace_back("double blink");
    if (signal & 4)  result.emplace_back("close your eyes");
    if (signal & 8)  result.emplace_back("jump");
    if (signal & 16) std::reverse(begin(result), end(result));

or its hexadecimal value

    if (signal & 0x01)  result.emplace_back("wink");
    if (signal & 0x02)  result.emplace_back("double blink");
    if (signal & 0x04)  result.emplace_back("close your eyes");
    if (signal & 0x08)  result.emplace_back("jump");
    if (signal & 0x010) std::reverse(begin(result), end(result));

The emplace_back() function is used to add the action to the result vector if the action's value is contained in the input signal.

If the reverse value is contained in the input signal, then the reverse() function is used to reverse the elements in the result vector.

The begin() and end() member functions could be called as free functions like so

if (signal & 0x010) std::reverse(result.begin(), result.end());

The result will be the same (at least in this exercise.)

When all of the if statements are gone through, the function returns the result vector.