Switch and default: for C - c

Question

Sorry if this sounds like a very basic question, it is my first time on here!
I am having some difficulties with coding for C, specifically with a switch and the default of that switch. Here is some example code:
#include<stdio.h>
int key;
main()
{
while((key=getchar())!=EOF)
{
printf("you pressed %c \n",key);
switch(key){
case'0':
case'1':
case'2':
case'3':
printf("it's a numeral\n");
break;
default:
printf("it's not a numeral\n");
}
}
}
The actual code is a bunch longer, this is purely an example.
So the code compiles it and I execute it, but I get:
"You pressed 1, it's a numeral, you pressed , it's not a numeral."
My code seems to 'fall through' and repeat itself without referring to either one. If anyone could help that would be great as this is an example in a text book and I am utterly stuck!
Kindest Regards.

Answer 1

You need to account for entering the Enter key, which produces a '\n' on *nix systems. I am not sure what pressing the Enter key does on Windows systems.
Here's your original code doctored up to eat the return key.
#include<stdio.h>
int key = 0;
main()
{
while((key=getchar())!=EOF)
{
if('\n' == key)
{
/* Be silent on linefeeds */
continue;
}
printf("you pressed %c \n",key);
switch(key){
case'0':
case'1':
case'2':
case'3':
printf("it's a numeral\n");
break;
default:
printf("it's not a numeral\n");
}
}
}
You maybe using getchar() for a specific reason, but my experiences in C usually involved reading the whole line, and RTL functions like scanf will eat the line terminator for you.

Answer 2

You need to eat the newline character, that is put in the read buffer when you hit return.
Issue another call to getchar after or before the switch to solve your problem.

Answer 3

Here is an idea...immediately before the printf(), insert logic to ignore spaces and all control characters...
if(key <= ' ')
continue;
printf(...) ...

Answer 4

I dont know if that is the problem, but you have three case without a break. So you press key "1" and there is nothing to do for the programm and so ins go to the next case how is right and this is the default.
Although you take a char in an int-variable???
In your Example it is a better way to take a if-clause like this:
#include<stdio.h>
char key;
main()
{
while((key=getchar())!=EOF)
{
printf("you pressed %c \n",key);
if(key == '0' || key == '1' || key == '2' || key == '3'){
printf("it's a numeral\n");
}
else {
printf("it's not a numeral\n");
}
}
Code is not tested. ;-)
The best way in bigger programms is to work with regular expressions.
I hope, this answer was helpful.

Answer 5

the problem might be due to, input buffer not flushing. when "1" is matched in the switch case, a newline character remains in the buffer.
try this,
fflush(stdin)