EOF not working as expected (C) - c

Question

I'm trying to use the EOF function but it doesn't work as I expect it. In the debugger mode it doesn't detect the second "scanf" function and just carries on. It keeps on missing out the "scanf" function now and then. Code is posted below
int main() {
char tempString;
int i = 0;
printf("Enter your letter\n");
scanf_s("%c", &tempString);
while (tempString != EOF) {
printf("You entered:%c\n", tempString);
scanf_s("%c", &tempString);
}
}
I have also tried it using the getchar() function but the same thing occurs, code is posted below:
int main() {
char tempString;
int i = 0;
printf("Enter your letter\n");
while ((tempString = getchar()) != EOF) {
printf("You entered:%c\n", tempString);
}
}
Thanks for reading

Answer 1

EDIT:
Firstly you omitted the length argument required by scanf_s for %c and %s formats.
Second, the %c format takes the next character from the input buffer. At the second (and subsequent) entries there was a newline left in the input buffer from the first input. Adding a space before the %c format specifier cleans off that leading whitespace.
Other formats, such as %s and %d do ignore leading whitespace, but not %c.
Thirdly, with scanf the use of EOF is not the way to go, you should control the loop with the return value from scanf which tells you the number of items successfully read.
This program starts by using scanf_s. The second entry ignores the newline after the first entry.
Then it moves to using getchar. In this test the function return value is int, so that's my data type here. That way EOF (-1) won't conflict with any required character data. Note that getchar starts by reading the newline left after the previous scanf_s (which only ignores leading whitespace.
#include <stdio.h>
int main(void)
{
char ch_scanf; // char type
int ch_getchar; // int type
printf("Using scanf_s\n");
if (scanf_s(" %c", &ch_scanf, 1) == 1) { // consumes any leading whitespace
printf("scanf_s value: %d\n", ch_scanf);
}
if (scanf_s(" %c", &ch_scanf, 1) == 1) { // consumes any leading whitespace
printf("scanf_s value: %d\n", ch_scanf);
}
printf("\nUsing getchar\n");
while ((ch_getchar = getchar()) != EOF) {
printf("getchar value: %d\n", ch_getchar);
}
return 0;
}
Sample session:
Using scanf_s
A
scanf_s value: 65
B
scanf_s value: 66
Using getchar
getchar value: 10
C
getchar value: 67
getchar value: 10
^Z
Finally if you want to use the standard library function scanf without MSVC ticking you off, you can do it like this
#define _CRT_SECURE_NO_WARNINGS
#include <stdio.h>

Answer 2

try this
#include <stdio.h>
int main(void) {
char tempString;
printf("Enter your letter\n");
while (scanf_s("%c%*c", &tempString, 1) != EOF) {//%*c for consume newline, 1 is buffer size
printf("You entered:%c\n", tempString);
}
return 0;
}
int tempString;//int for check EOF
printf("Enter your letter\n");
while ((tempString = getchar()) != EOF) {
printf("You entered:%c\n", tempString);
getchar();//consume newline
}

Answer 3

The behaviour of scanf() function in C
Is to read the input from the keyboard buffer till it encounters EOF (ie; till we
press enter key)
In general, it is not advisable to use "%c" in C to read an input character because
The value is collected in keyboard buffer till we hit enter and we could not restrict user entering single character
So, the best way to obtain a character is by using getchar() function.
In the program you have provided you can use any other character to check for end and not EOF since it is used in scanf() implementation to mark the input end.
You may other keys like esc to check for the end
#include <stdio.h>
#include <stdlib.h>
#define esc 27
int main()
{
char ch;
while((ch = getchar()) != esc) {
//print the entered character here
}
}
To know in depth about scanf() implementation look into this scanf() source code