do something special when user input empty line

Question

Hi,

I'm just starting to study C. I have a program that prints a menu and let users choose what to do step by step. Now I would like to return to the main menu whenever the user enters an empty line, but how can I do that?
I think I can make a function that return the program to the main menu, but when to call that function? I know it's not good to put an if-else whenever I scanf something...

I am used to the OO world, so this is a bit unfamiliar to me, please help :)

Answer 1

C language is not an OO world, so I'd say stick with if-else. Anyway, when creating text menus you usually end up with switch(user_choice) of if-else.

Do you need a help with scanf()?

Answer 2

If you're doing something along the lines of:

printf("0)     do something\n");
printf("1)     do something else\n");
printf("enter) main menu\n");

...then scanf isn't really your friend.

You could do something like this:

char buf[80];  
int choice;
printf(menu_text);
fgets(buf, 80, stdin);
if(strlen(buf))
{
    sscanf(buf, "%d", &choice);
    switch(choice)
    {
    case 0:
        /* etc */
        break;
    case 1:
        /* etc */
        break;
    }
}
else
{
    go_back_to_main_menu();
}

Answer 3

It depends on if the user is communicating by sending a string or a single character/keypress.

If communicating by string, try starting with:

char  buffer[MAX_BUF_LEN];
char* pBuffer = buffer;
scanf("%s%*c",pBuffer);
if (strlen(pBuffer) == 0)
  goto_main_menu();
else
  process_user_input(pBuffer);

If communicating by character/keystroke, try starting with:

int inkey = getchar();
if (inkey == '\n')
  goto_main_menu();
else
  process_user_input(inkey);

Using an "if/else" after you scanf something is perfectly valid. Anything sent from the user should be checked and validated before it is used anyway.

Answer 4

I'm guessing you're using a switch statement to filter your input, so just make an option for '\n', or the newline character, to output the print the menu.