如何正确设置开关状态循环？

Question

When the characters AB or C are entered it returns their numerical value.

The Default statement prints if anything is entered for the first time. THEN if you enter AB or C it prints properly but after that the Default statement prints no matter what.

/*#define_USE_C99_MATH*/
/*#include <stbool.h>*/
#include <stdio.h>

main ()
{
    int ABC;     /* I/O */
    char c1 = 'A'; /*Characters to be entered*/
    char c2 = 'B';
    char c3 = 'C';

    /*typedef enum { false, true } bool;*/
    printf("Please enter either A, B, or C (case sensitive):");
    ABC = getchar();
    /*bool loop = true;*/

    if ((ABC = getchar()) == c1 | c2 | c3)
    {
        do
        {
            switch (ABC)
            {
            case 'A':    
                printf("The numerical value of A is: %d\n", c1);
                break;

            case 'B':    
                printf("The numerical value of B is: %d\n", c2);
                break;  

            case 'C':    
                printf("The numerical value of C is: %d\n", c3);
                break;  

            default:
                printf("The character you have entered is not valid.\n");
                break;
            }
        } while ((ABC = getchar()) != c1 | c2 | c3);
    }
    else
    {
    }

    return 0;
}

Answer 1

Your error seems to be that you have entered an if statement which will work only if you enter 'A' 'B' or 'C'. In my opinion though, i think it would be better to not use if statements in this program. Rather, just keep the do while loop and the code will run fine.

Answer 2

You should be using logical-OR || instead of the bitwise-OR | ( you can still use | in this case but it helps the code be more readable ). And you can encounter a problem with using input functions because when the user enters an input via getchar() it actually sends 2 characters, say A and \\n so you need to consume the newline again via getchar()

I've modified your code here, but it still does the same behavior:

#include <stdio.h>

main ()
{
    char ABC;
    char c1 = 'A';
    char c2 = 'B';
    char c3 = 'C';

    printf("Please enter either A, B, or C (case sensitive):");
    ABC = getchar();

    while(ABC != c1 && ABC != c2 && ABC != c3)
    {
        getchar(); // Consume \n
        printf("The character you have entered is not valid.\n");
        ABC = getchar();
    }

    switch (ABC)
    {
    case 'A':    
        printf("The numerical value of A is: %d\n", c1);
        break;

    case 'B':    
        printf("The numerical value of B is: %d\n", c2);
        break;  

    case 'C':    
        printf("The numerical value of C is: %d\n", c3);
        break;  
    }

    return 0;
}

Answer 3

Why not just remove the if statement, because if you do that you will have a chance to have your default case be true, another reason why you may be having errors is due to this:

while ((ABC = getchar()) != c1 | c2 | c3);

make it into:

while ((ABC = getchar()) != c1 | ABC != c2 | ABC != c3);