为什么打印会发生两次

Question

任何人都可以告诉我为什么printf语句被执行2次？

do {

    printf("\n Enter the choice: a to add, d to display, q to exit: ");
    scanf("%c",&choice);

    switch(choice) {
        case 'a':
            addData();
            break;

        case 'd':
            display();
            break;
    }
} while (choice != 'q'); 

我期待以下内容：

Enter the choice: a to add, d to display, q to exit: a Enter the choice: a to add, d to display, q to exit: d

但我得到以下内容：

Enter the choice: a to add, d to display, q to exit: a Enter the choice: a to add, d to display, q to exit: Enter the choice: a to add, d to display, q to exit: d

任何人都可以让我知道，中间线背后的问题是什么？

谢谢， Meghdeep