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Actual final

Sep 12, 20243 min read

This C++ code contains definitions for two functions that generate the lyrics of the song “The 12 Days of Christmas” in two different styles. Let’s go through each part of the code.

Preprocessor directives and global definitions

#include <fmt/format.h>
#include<bits/stdc++.h>
#define C std::cout<<
int /*whitespace*/ d, q;
std::vector /* must leave whitespace here */
   s { "st", "nd", "rd" },
   g { /* ... gifts ... */ };
  • #include <fmt/format.h> includes the fmt library which provides facilities for formatting and printing.
  • #include<bits/stdc++.h> is a GCC-specific header that includes most of the standard C++ library headers. This is not a best practice and should generally be avoided in favor of including only necessary headers.
  • The #define C std::cout<< defines a macro to abbreviate the std::cout << statement.
  • int /*whitespace*/ d, q;: Variables d and q are defined as global integer variables and are initialized to 0.
  • std::vector /* must leave whitespace here */ defines two vectors s and g. Vector s contains ordinal number suffixes, and vector g contains the gifts from the song.

Function DaysOfChristmas_smallCode

void DaysOfChristmas_smallCode() {
   /* ... function code ... */
}

This function prints the lyrics using loops and a macro. It uses the C macro to print to std::cout. It iterates over the 12 days, using the d variable for days and q for the “quantity” of gifts. The comma operator and conditional operator (?:) are used in a way that might appear non-intuitive but are valid C++.

Namespace statement

using namespace std;

This line allows all standard library names to be used without the std:: prefix. This is generally discouraged in larger projects due to the risk of name collisions.

Function processGift

void processGift(const int &day) {
   /* ... function code ... */
}

This function uses the fmt::format function to format and print the appropriate gift line, it maintains a static counter count that is incremented every time the function is called.

Function DaysOfChristmas_switch2

inline void DaysOfChristmas_switch2 (int dayLimit = 6 ) {
   /* ... function code ... */
}

This function prints a different version of the song for a custom dayLimit. It uses switch statements to handle each day’s suffix and to call processGift with appropriate arguments.

main function

int main( ) {
   /* ... main code ... */
}

The main function demonstrates various uses of the variable name q which is also a global variable. It’s meant to show a potential for confusion during debugging due to variable shadowing and scope.

  1. constexpr long long q{1}; and const double q{2.2}; locally shadow the global q.
  2. for (char q{'a'}; auto &e : s) uses a local q for a loop variable.
  3. array<string, 12> s; is an std::array that is distinct from the global s.
  4. std::accumulate is used twice to concatenate strings: first from the s array, then reverse concatenation of the g vector.
  5. Calls to DaysOfChristmas_smallCode() and DaysOfChristmas_switch2() invoke the two different song-producing functions.
  6. processGift(13); will throw an std::out_of_range exception because g only has 12 elements.

Finally, the main function returns the value of the global q.

Exception handling

catch (const std::out_of_range& ex) {
   /* ... catch block code ... */
}

The try block is around the body of the main function, and the catch block is designed to catch out-of-range exceptions, output an error message, and return 3.

Overall, the code brings together several aspects of C++ (classes, loops, conditionals, exception handling, etc.) and uses them in a context that could potentially be confusing, as it is designed to demonstrate and test understanding of variable scope, headers inclusion, preprocessor directives, and exception handling mechanisms.

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