Software 1 - Introduction, getchar(2)

Administrivia

Practice Web Page - http://www.cs.tau.ac.il/~efif/courses/Software1_Summer_03

Overview of the course

• C programming
• Unix programming - C shell - basic unix commands

Homework

• an assignment every two weeks
• singleton submission
• assignments are worth 20%-30% of total grade
  • final exam is worth 80%-70%

Homework Issues

• you can use your home computer
• you can use your friend’s computer
• you can use any computer you like
• but the programs you submit must work on the Unix system in the lab.
  • you use any of the options above at your own risk
• see Submission Guidelines for precise instructions

Working from home at your own risk

• develop the code with the available tools
• copy the files that contain the source code later to the university
• compile again at the univerisy to verify that everything works

Developing at home

• locally - on a local machine
• remotely - on a university machine

Developing on a local machine (at home)

• install linux - if you are brave!
• install cygwin - a UNIX environment for Windows
  1. a DLL (cygwin1.dll) which acts as a UNIX emulation layer providing substantial UNIX API functionality.
  2. a collection of tools, ported from UNIX, which provide UNIX/Linux look and feel

Windows

• install a few tools including the gnu compiler from cygwin
• use Dev-C++ - a full-featured Integrated Development Environment (IDE) for Win32. Thank you Assaf Lavie for pointing it out to me.
  • Uses GCC, Mingw or Cygwin as compiler and libraries set
• use Microsoft tools from the command line
  • you need to add the directory where all the tools are to your search path (PATH environment variable)
• use MSVC project
  • developing C\C++ using Microsoft Visual C++ 6.0, courtesy of the system dep.English Hebrew

Copying Files and Accessing the Unix computers in CS

• use WinSCP to copy files (secure copy protocol)
• use SSH to login relotely (secure shell)
• visit the system for all the relevant information and downloads

Account, labs, printing, and email

• if you don't have an account on the Unix system, you need to open one
• if you have an account, make sure you change your password

  passwd

• list of printers and instructions can be found at system FAQ for printing
• all sorts of useful information at the system FAQ http://www.cs.tau.ac.il/faq

so let's look at the whole process

• write a program
  • text editor
• compile the program
  • C compiler
  • will do one of two things:
    • print error messages and abort
    • produce an executable program
• run the program

Editors

• vi - a programmers text editor
• pico - simple text editor in the style of the Pine Composer
• emacs - GNU project Emacs
  • the user functionality of GNU Emacs encompasses everything other Emacs editors do, and it is easily extensible since its editing commands are written in Lisp
  • xemacs - a version of emacs
  • .emacs - an initialization file example
• Dev-C++ built in
• Microsoft - MSVC project built in (only on windows...)
• Editor of your choice

Character Input and Output

• printf - format and print data
• scanf - scan and format input
• getchar - read a character

  int getchar(void);

• putchar - write a character

  int putchar(int ch);

getchar

• most basic way of reading input
• reads one character from the "standard input"
  • usually the user's keyboard, but
  • can sometimes be redirected by the operating system.
• returns (rather obviously) the character it reads, or,
  • if there are no more characters, the special value EOF "end of file"

getchar example

• reads one character
• as long as the character read is not EOF prints it and reads another in a loop

  main() { int c; c = getchar(); while(c != EOF) { putchar(c); c = getchar(); } return 0; }

getchar return type

• a char variable can hold integers corresponding to character set values
• an int can hold integers of more arbitrary values (up to +-32767)
• most character sets contain a few hundred characters (nowhere near 32767)
  • an int variable can in general comfortably hold all char values
• there's nothing wrong with declaring c as an int
• it's important to do so, because getchar can return every character value, plus that special, non-character value EOF
  • otherwise, possibly mix it up with some actual character value

EOF

• the program stops when it receives end-of-file (EOF),
  • EOF indicates the absence of any more characters to read
• generating EOF is operating system dependent
  • Unix and Unix-related systems - almost always control-D.
  • MS-DOS machines - control-Z followed by the RETURN key.
  • Think C on the Macintosh - control-D, just like Unix.
  • other systems require some research to learn how to send EOF.
• the character you type to generate an end-of-file is not the same as the special EOF value returned by getchar.
  • the EOF value returned by getchar is a code indicating that the input system has detected an end-of-file condition
    • in a disk file there is no EOF

Terminating a program

• if a program is running forever waiting for input
  • stop it by sending it an end-of-file, as above
• if it's running forever not waiting for something
  • you'll have to take more drastic measures.
    • under Unix, control-C (or, occasionally, the DELETE key) will terminate the current program, almost no matter what.
    • under MS-DOS, control-C or control-BREAK will sometimes terminate the current program
    • on the Mac, try command-period or command-option-ESCAPE.

Shorter getchar example

while((c = getchar()) != EOF) putchar(c);

• an assignment expression has a value, remember?
• the extra parentheses around

  (c = getchar())

  are important, because the precedence of the != operator is higher than that of the = operator