Macro Constants

An object-like macro can name a compile-time text replacement, while a normal variable still changes at runtime.

macro_constants.cpp

#include <iostream>

#define TAX_PERCENT 8

#if TAX_PERCENT == 8
constexpr int taxPercent = 8;
#else
constexpr int taxPercent = 0;
#endif

int main() {
    int subtotal = ;

    int tax = subtotal * taxPercent / 100;
    int total = subtotal + tax;

    std::cout << "subtotal=" << subtotal << std::endl;
    std::cout << "tax=" << tax << std::endl;
    std::cout << "total=" << total << std::endl;
    return 0;
}

#include <iostream>

#define TAX_PERCENT 8

#if TAX_PERCENT == 8
constexpr int taxPercent = 8;
#else
constexpr int taxPercent = 0;
#endif

int main() {
    int subtotal = ;

    int tax = subtotal * taxPercent / 100;
    int total = subtotal + tax;

    std::cout << "subtotal=" << subtotal << std::endl;
    std::cout << "tax=" << tax << std::endl;
    std::cout << "total=" << total << std::endl;
    return 0;
}

#include <iostream>

#define TAX_PERCENT 8

#if TAX_PERCENT == 8
constexpr int taxPercent = 8;
#else
constexpr int taxPercent = 0;
#endif

int main() {
    int subtotal = ;

    int tax = subtotal * taxPercent / 100;
    int total = subtotal + tax;

    std::cout << "subtotal=" << subtotal << std::endl;
    std::cout << "tax=" << tax << std::endl;
    std::cout << "total=" << total << std::endl;
    return 0;
}

macro constant A macro constant is replaced by the preprocessor before the compiler sees the program.