What do you call a variable whose value does not change during the program?

What do you call a simple function created using a replacement function?

 #include <stdio.h>

#define TRI(A, H) ((A) * (H) / 2)

int main(void)
{
    int side, high, square;

    scanf("%d,%d", &side, &high);
    printf("%d\n", TRI(side, high));

    return 0;
}

I created in Exercise 11, a
The program should display whether the Olympics will be held when the year of the year is entered.
However, the part of the program that calculates the date of the Olympics must be created as a separate function.
In addition, the return value of the function should be returned as an enum constant.

You could just write the number directly or use a variable, but you can't
Indirectly explain why you bother to use constants.

constant

macro

Macro to find the area of a triangular shape.

 #include <stdio.h>

int olympic(int year);

The enum {
    OLYMIPC_NON,
    OLYMIPC_SUMMER,
    OLYMIPC_WINTER,
};

int main(void)
{
    int year, hold;

    scanf("%d", &year);
    hold = olympic(year);

    switch (hold) {
    case OLYMIPC_NON:
        printf("not opened\n");
        break;
    case OLYMIPC_SUMMER:
        printf("Summer Olympics\n");
        break;
    case OLYMIPC_WINTER:
        printf("Winter Olympics\n"); break; case OLYMIPC_WINTER: printf("Winter Olympics\n")
        break;
    };

    return 0;
}

int olympic(int year)
{
    if (year % 2 == 0) {
        if (year % 4 == 0) {
            return OLYMIPC_SUMMER;
        } else {
            return OLYMIPC_WINTER;
        }
    } else {
        return OLYMIPC_NON;
    }
}

Naming them makes them easier to understand and prepare changes.
Furthermore, constants are not assignable, so the values cannot be changed by mistake, leading to the phenomenon of bugs.