What exactly is r in C language

Question

include  lt stdio h gt   int main       int countch 0    int countwd 1     printf  Enter your sentence in lowercase        char ch  a     while ch    r           ch getche        if ch             countwd        else       countch           printf   n Words   d   countwd      printf  Characters    d  countch-1      getch        This is the program where I came across  r  What exactly is its role here  I am beginner in C and I appreciate a clear explanation on this

User · Answer

It depends upon which platform you re on as to how it will be translated and whether it will be there at all  Wikipedia entry on newline

User · Answer

r   means carriage return    The  r means nothing special as a consequence For character-mode terminals  typically emulating even-older printing   ones as above   in raw mode   r and  n act similarly  except both in terms   of the cursor  as there is no carriage or roller   Historically a  n was used to move the carriage down  while the  r was used to move the carriage back to the left side of the screen

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It s Carriage Return  Source  http   msdn microsoft com en-us library 6aw8xdf2 v vs 80  aspx  The following repeats the loop until the user has pressed the Return key   while ch    r       ch getche

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Once upon a time  people had terminals like typewriters  with only upper-case letters  but that s another story    Search for  Teletype   and how do you think tty got used for  terminal device    Those devices had two separate motions   The carriage return moved the print head back to the start of the line without scrolling the paper  the line feed character moved the paper up a line without moving the print head back to the beginning of the line  So  on those devices  you needed two control characters to get the print head back to the start of the next line  a carriage return and a line feed  Because this was mechanical  it took time  so you had to pause for long enough before sending more characters to the terminal after sending the CR and LF characters   One use for CR without LF was to do  bold  by overstriking the characters on the line   You d write the line out once  then use CR to start over and print twice over the characters that needed to be bold   You could also  of course  type X s over stuff that you wanted partially hidden  or create very dense ASCII art pictures with judicious overstriking   On Unix  all the logic for this stuff was hidden in a terminal driver   You could use the stty command and the underlying functions  in those days  ioctl   calls  they were sanitized into the termios interface by POSIX 1 in 1988  to tweak all sorts of ways that the terminal behaved   Eventually  you got  glass terminals  where the speeds were greater and and there were new idiosyncrasies to deal with - Hazeltine glitches and so on and so forth   These got enshrined in the termcap and later terminfo libraries  and then further encapsulated behind the curses library   However  some other  non-Unix  systems did not hide things as well  and you had to deal with CRLF in your text files - and no  this is not just Windows and DOS that were in the  CRLF  camp   Anyway  on some systems  the C library has to deal with text files that contain CRLF line endings and presents those to you as if there were only a newline at the end of the line   However  if you choose to treat the text file as a binary file  you will see the CR characters as well as the LF   Systems like the old Mac OS  version 9 or earlier  used just CR  aka  r  for the line ending   Systems like DOS and Windows  and  I believe  many of the DEC systems such as VMS and RSTS  used CRLF for the line ending   Many of the Internet standards  such as mail  mandate CRLF line endings   And Unix has always used just LF  aka NL or newline  hence  n  for its line endings    And most people  most of the time  manage to ignore CR   Your code is rather funky in looking for  r   On a system compliant with the C standard  you won t see the CR unless the file is opened in binary mode  the CRLF or CR will be mapped to NL by the C runtime library

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r  is the carriage return character  The main times it would be useful are    When reading text in binary mode  or which may come from a foreign OS  you ll find  and probably want to discard  it due to CR LF line-endings from Windows-format text files  When writing to an interactive terminal on stdout or stderr    r  can be used to move the cursor back to the beginning of the line  to overwrite it with new contents  This makes a nice primitive progress indicator    The example code in your post is definitely a wrong way to use   r   It assumes a carriage return will precede the newline character at the end of a line entered  which is non-portable and only true on Windows  Instead the code should look for   n   newline   and discard any carriage return it finds before the newline  Or  it could use text mode and have the C library handle the translation  but text mode is ugly and probably should not be used

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There are a few characters which can indicate a new line  The usual ones are these two    n  or  0x0A   10 in decimal  -  This character is called  Line Feed   LF     r  or  0x0D   13 in decimal  -  This one is called  Carriage return   CR    Different Operating Systems handle newlines in a different way  Here is a short list of the most common ones   DOS and Windows  They expect a newline to be the combination of two characters  namely   r n   or 13 followed by 10    Unix  and hence Linux as well   Unix uses a single   n  to indicate a new line   Mac  Macs use a single   r

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That is not always true  it only works in Windows  For interacting with terminal in putty  Linux shell     it will be used for returning the cursor to the beginning of line  following picture shows the usage of that   Without   r       Data comes without   r  to the putty terminal  it has just   n     it means that data will be printed just in next line        With   r         Data comes with   r   i e  string ends with   r n   So the cursor in putty terminal not only will go to the next line but also at the beginning of line

[c] What exactly is \r in C language?

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