ending program using '\0' in c programming- while loop

Question

I have trouble finishing a while loop using '\0' in c programming language, the c code is the following

#include<stdio.h>

char r;

int main()
{
    do 
    {
        scanf("%c", &r );
        printf("%c", r);
    }
    while (r!='\0');

    return 0;
}

My problem is that the program never finishes at the final character of typed string line, the while loop is always in waiting mode because of the scanf and never go to return 0. I do not know why this happen.

The output of this program is like this:

1234
2345
4556
7788
2345, 4556, 7788

Those are numbers I typed, but the program never finish (never go to return 0), I want to print just one string and I want the program ends.

You can't enter zero. Change it to %d and `int` or compare the char value with '0' — 0___________, Feb 05 '18 at 02:44
how can i finish a string? how can i know the end of a string? and then print the typed string? is it possible to use "/0" to know the end of the string? — Omar Elio Torres Castillo, Feb 05 '18 at 02:47
You do not have any strings there. So there is nothing to terminate with zero — 0___________, Feb 05 '18 at 02:48
the strings are typed by the user, for example a 1234, 2345, etc... but the program never finishes, i want the user type one string and then the program prints the string after that i want the program end (while loop finish) — Omar Elio Torres Castillo, Feb 05 '18 at 02:52
i am using "\0" the null character in order to end the string — Omar Elio Torres Castillo, Feb 05 '18 at 02:53
But you do not have a string there. What string? String is a char table. You only have char — 0___________, Feb 05 '18 at 02:55
yes, i made a mistake, the user typed several characters and it supposed the program finishes when find the /0 null character, thanks for the suggestion above — Omar Elio Torres Castillo, Feb 05 '18 at 02:57
@PeterJ_01 `'\0'` can be enter. Various keyboards allow it or a file can be piped into `stdout` — chux - Reinstate Monica, Feb 05 '18 at 03:58
first, check if the input value is printable, before trying to print it. (the `isprint()` function from `ctype.h`) Second, a 0x00 ('\0') byte can be entered via , however, much easier to just check for the terminating '\n' (newline) character. — user3629249, Feb 05 '18 at 04:08
suggest checking the returned value (not the parameter values) from the call to `scanf()`. In the current scenario, the returned value will be 1 unless an error occurs or the user enters (depending on the OS) or — user3629249, Feb 05 '18 at 04:10
@chux I don't think, he asked about entering the char using the alphanumeric values. — 0___________, Feb 06 '18 at 07:57

chux - Reinstate Monica · Answer 1 · 2018-02-05T17:14:12.947

Typical user input is a line, a sequence of characters up to and including a final '\n'.

As a part of user input, '\0' is just another character. It is often difficult to key in. Some keyboards allow it with CtrlShift@ or other ways @user3629249

Very rarely is a string (a sequence of characters up to and including a final '\0') used on input.

To handle user input, a simply approach is to use fgets() to read a line of user input. That input will be saved as a string by fgets(buf) by appending a null character '\0' to the characters read: all saved in buf.

#include<stdio.h>

int main(void) {
  char buf[100];
  if (fgets(buf, sizeof buf, stdin) == NULL) {
    puts("End-of-file or error encountered");
  } else {
    // maybe lop off the potential trailing \n from buf
    buf[strcspn(buf, "\n")] = '\0';
    printf("User input was <%s>\n", buf);
  }
  return 0;
}

To end user input, the usual approach is to signal the "end-of-file", see recognise return as EOF on the console

If code must use scanf();, check the return value to detect end-of-file or input error. @user3629249

if (scanf("%c", &r ) != 1) {
  puts("End-of-file or error encountered");
}

@OmarElioTorresCastillo: I see it's been a while since you last asked a question here. Accepting an answer is still the proper thing to do (and merely commenting "thank you" still is not). — Jongware, Feb 05 '18 at 14:19

ending program using '\0' in c programming- while loop

1 Answers1