how do i have constant value without a global variable in C using functions

December 2, 2021

So, i have this code:

#include <stdio.h>



void menu_loop(int run) {
    if (run == 0) {
        printf("bad\n");
        menu();
    }
    else
        printf("good");
}
int check_menu(int menu1) {
    if (menu1 > 3 || menu1 < 0)
        return 0;
    else
      return 1;
}
int menu() {
    int choice;
    printf("----MENU----\n0 -> Exit\n1 -> Prime time\n2 -> Calander calculating\n3 -> Matrix printing\n");
    scanf_s("%d", &choice);
    int check2 = check_menu(choice);
    menu_loop(check2);
}


void main() {
    menu();
}

what i need to do is whenever check_menu returns a 0 then i need to have a certein variable that starts at 0 go up by 1.
everytime i try this i find that the value gets reinitialized to 0 since im initializing it inside the function.
thanks in advance!

>Solution :

Returning an error code from a function in case something bad has happened is a common practice in C as it doesn’t has a concept of throwing an exception as in more high level languages. I recommend you defining a macro to be more explicit and use a loop instead of recursion.

#include <stdio.h>

#define INVALID_CHOICE_ERR 1

int check_menu(int menu1)
{
    if (menu1 > 3 || menu1 < 0)
        return INVALID_CHOICE_ERR;
    else
        return 0;
}

int menu()
{
    int choice;
    do {
        printf("----MENU----\n0 -> Exit\n1 -> Prime time\n2 -> Calander calculating\n3 -> Matrix printing\n");
        scanf_s("%d", &choice);
    } while (check_menu(choice) == INVALID_CHOICE_ERR);
    // Now that a valid choice has been selected, you can use it
}

void main()
{
    menu();
}

Or you can get rid of the macro and function by simplifying the while loop