Scanf only works alternately

Question

I am facing a problem with the code below. As the output shows, after calling scanf("%c", &choice); the first time, scanf seems to stop working for next iteration and the default case is executing. However after that scanf works fine one more time and then doesn't work the next time. This cycle goes on. I am not able to understand the issue. What is the reason?

Code:

int main()
{
    char choice;
    int value;
    node *root = NULL;
    printf("\tA. add node\n\tB. inorder\n\tC. pre order\n");
    printf("\tD. delete node\n\tE. post order\n\tF. Ascending\n");
    printf("\tD. Descending\n");
    do {
        printf("Enter your choice\n");
        scanf("%c", &choice);
        switch (choice) {
            case 'A':
                printf("Enter value\n");
                scanf("%d", &value);
                addnode(&root, value);
                break;

            case 'B':
                inorder(root);
                break;

            case 'C':
                preorder(root);
                break;

            case 'D':
                printf("Enter value\n");
                scanf("%d", &value);
                deletenode(&root, value);
                break;

            case 'E':
                postorder(root);
                break;

            case 'F':
                ascending(root);
                break;

            case 'G':
                descending(root);
                break;

            case 'X':
                printf("Good Bye\n");
                break;

            default:
                printf("Enter proper choice\n");
                break;
        }
    } while(choice != 'X');
    return 0;
}

Output:

        A. add node
        B. inorder
        C. pre order
        D. delete node
        E. post order
        F. Ascending
        D. Descending
Enter your choice
A
Enter value
2
Enter your choice
Enter proper choice
Enter your choice
A
Enter value
4
Enter your choice
Enter proper choice
Enter your choice
D
Enter value
4
Enter your choice
Enter proper choice
Enter your choice
.
.
.

numerous dupes of this one. don't use `scanf()`. use `fgets()` and parse the input after reading. — The Paramagnetic Croissant, Dec 10 '15 at 08:54
@ameyCU no, just don't. that only suppresses the symptom, it doesn't cure the disease. — The Paramagnetic Croissant, Dec 10 '15 at 08:55

August Karlstrom · Accepted Answer · 2015-12-10T09:31:26.810

2

You need to skip leading whitespace (previous newline) when reading the choice. Just add a space before %c in the format string:

scanf(" %c", &choice);

edited Dec 10 '15 at 09:31

answered Dec 10 '15 at 09:05

August Karlstrom

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Scanf only works alternately

1 Answers1