Terminate a while loop using `getchar()`

Question

For my homework assignment, I need to implement Horners Algorithm for converting between bases.

I have been told to use getchar() for this assignment. But I am having a problem where when I hit enter, the program doesn't terminate and just takes in more chars.

Example:

bryce> ./pa1 Enter the fromRadix:16 Enter the toRadix:2 abc abc ^C bryce>

Code:

int readRadixA(int radixA) { char myChar = getchar(); int result = 0; int run = 0; while(myChar != EOF) { if(myChar == "\n") break; Horners(); myChar = getchar(); } return result; }

I am not asking for help implementing Horners; I am asking for help to terminate the getchar() correctly.

Have you tried ^D, the EOF character of Unix shells? :) On Windows, ^Z might work in this role. You could also consider finishing your program on two \ns in a row (that is, typing an empty line). — 9000
– 9000, Commented Feb 4, 2012 at 7:51
getchar returns an int. Not a char, an int. myChar needs to be an int. — Mat
– Mat, Commented Feb 4, 2012 at 7:51
thank you @9000 , your reply helped me. i use Debian 10 on virtualbox 6.1.2 — Dev
– Dev, Commented Feb 28, 2020 at 14:54

cnicutar · Accepted Answer · 2012-02-04 08:51:39Z

5

if(myChar=="\n") ^ ^

You're comparing myChar wrong. Try this instead:

if(myChar == '\n') ^ ^

A second problem is that getchar returns int, not char. Maybe you can rewrite it like this:

int myChar; while((myChar = getchar()) != EOF && myChar != '\n') { /* Your stuff. */ }

EDIT

In light of comments, I think some stdio operation before that while is leaving a \n in the buffer.

Instead of scanf("%d", &radix) try:

scanf("%d ", &radix); ^

That space will make scanf eat the remaining blanks (including the newline).

edited Feb 4, 2012 at 8:51

answered Feb 4, 2012 at 7:50

cnicutar

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6 Comments

Snow_Mac Over a year ago

I try that, and my program immediately terminates after I enter my commands for enter radix from and to. Meaning I cannot input into the get char.

cnicutar Over a year ago

@Snow_Mac What did you enter ? What did you expect ?

Snow_Mac Over a year ago

Program prompts me: Enter the fromRadix:, then I type 16, then it prompts:Enter the toRadix:, then I type 2. After this is where my method gets called with getchar(); which I should be able to type abc.

Snow_Mac Over a year ago

I'm doing this via a Mac SSHed into a linux box.

Michael Burr Over a year ago

@Snow_Mac: I'd bet that the code that reads in fromRadix and toReadix (scanf() I bet) is leaving the '\n' in the buffer, so it's the first character returned by getchar() when readRadixA() is executed.

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FatalError · Accepted Answer · 2012-02-04 07:50:31Z

Check the return type of getchar(). Yes, it's an int. That's because EOF must have a value that can be distinguished from a valid character. myChar must actually be made to be int.

Sunil Kumar B M · Accepted Answer · 2012-02-04 07:53:24Z

0

Try this code

int readRadixA(int radixA) { char myChar; int result = 0; int run = 0; do { myChar = getchar(); // implement horners here }while(myChar != 13); return result; }

answered Feb 4, 2012 at 7:53

Sunil Kumar B M

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3 Comments

Mateen Ulhaq Over a year ago

What's up with the 13? Don't you know it's unlucky?

Sunil Kumar B M Over a year ago

13 is the ascii value of ENTER key

Mateen Ulhaq Over a year ago

But it is not immediately obvious to those who have not had their ASCII tables memorized. And it's a carriage return, BTW, not the "Enter" key. If you insist on not using '\r', at least use the conventional 0x0D. But then again, a linefeed, 10, 0x0A, or '\n' is much more standard than a carriage return.

rakesh · Accepted Answer · 2012-02-04 09:19:59Z

I checked your code I think you are leaving a '\n' in the input keyboard buffer after the toRadix.

And their is one more thing that

 getchar()

reads all the characters in one go till a '\n' is received.

And there is one more mistake you have committed by comparing a

 char to a pointer e.g mychar=="\n"

further information about your implementation of toRadix can be really helpful to answer your question

Basile Starynkevitch · Accepted Answer · 2017-11-26 08:03:43Z

On linux, to end the standard input, you have to type Ctrl-D. The kernel and tty layers makes that an end-of-file mark or condition. Then getchar gives EOF (which is not a valid char, for example on systems where char are unsigned bytes between 0 and 255, EOF could be -1).

Notice that feof(3) is valid only after a read operation (e.g. getchar, fgets, etc...) so coding while(feof(stdin)) is generally wrong (contrarily to what I wrote in the previous version of this answer). You'll better test that getchar is returning EOF so your myChar should be an int (not a char).

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