Scanf is being ignored, how to prevent? - c

Question

I got this code:
#include <stdio.h>
int main(void){
char ordet;
int again = 1;
while(again == 1){
printf("Write a name: \n");
while (ordet!='\n'){
scanf("%c",&ordet);
if('A'<= ordet && ordet <='W')
{
printf("%c",ordet+3);
}
else if('W'<=ordet){
printf("%c", ordet-22);
}
}
printf("\nDo you want to write a new name? 1/0");
scanf("%d", &again);
}
return 0;
}
It runs fine the first time but as soon as you press 1 to write a new name you never get the chance to write it, it just keeps asking "Do you want to write a new name?" and ignores "Write a name:". I have tested with fflush(stdin), != EFO and space infront of %c but nothing works. How could I fix this since I really have no idea, started out with C a few days ago.

Answer 1

while (ordet!='\n'){
ordet is used without initialization here. Not quite UB (if your implementation uses unsigned char or signed char has no trap-representations), but bad enough.
scanf("%c",&ordet);
The above line is the only line potentially setting ordet. Please take note that the loop starting with it is only entered when ordet is not '\n'.
You probably want to reset it before entering the inner loop, or use a do-while-loop.
Actually, changing both loops to do-while-loops would be good.
scanf("%d", &again);
The above line reads a number from beginning of stdin, but leaves the newline.
This must be dealt with by consuming all whitespace on repeat.
Luckily, that's easily done as the inner loop ignores whitespace.
Change "%c" to " %c".
Also, all your scanf-invocations can fail. Check them!

Answer 2

There are 2 problems with your code:
ordet is not initialized before its first usage. It is undefined behavior.
You do not reset ordet anywhere outside the inner loop. That is, once ordet becomes equal to \n, the body of the inner loop is never executed again.
To fix it, you can write something like ordet = 0 before inner loop. And don't forget to skip new line character that is left in the buffer after reading again variable.

Answer 3

All input you write in the console from the keyboard is placed in a buffer, scanf reads from this buffer however if there are more characters in the buffer than what your format specifier specifies those characters will remain in the buffer.
e.g.
scanf( "%d", &n );
when you enter a numerical value 100 and press ENTER afterwards, the ENTER character is placed in the buffer as well "100\n" when you do scanf on the buffer (stdin) the 100 is extracted from the buffer but the \n remains.
Next time you write scanf("%d", &n ); the \n is still in there and will not be read by %d since it is not a %d number.
IMO the best way to handle this is instead to read from the keyboard using fgets, then after the content has been read use sscanf to extract the information you want:
char buffer[128];
fgets( buffer, sizeof(buffer), stdin );
sscanf( buffer, "%d", &n );
you also then can have additional error checks:
if (fgets( buffer, sizeof(buffer), stdin ) != NULL )
{
if (sscanf( buffer, "%d", &n ) ==1)
{
...
}
}
now to your code:
if you want to read character by character from the keyboard use fgetc() not scanf()
Use the C-runtime function isalpha()/toupper() to recognize a character.
In C, a character is an int, that is why most functions like fgetc return an int and not a char.
In general I would recommend using fgets() instead of reading one character at a time.