Software 1 - standard library, bases, getchar, getline (3)

Input and Output

• #include <stdio.h>

• int printf(const char *format, ...) - format and print data
• int scanf(const char *format, ...) - scan and format input
• int getchar(void) - read a character
• int putchar(int c) - write a character

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

getline

• Reading lines from the standard input

  #include <stdio.h> /*! getline() reads one line from standard input and copies it to line array * (but no more than max chars). * It does not place the terminating \n in line array. * Returns line length, or 0 for empty line, or EOF for end-of-file. */ int getline(char line[], int max) { int nch = 0; int c; max = max - 1; /* leave room for '\0' */ while ((c = getchar()) != EOF) { if (c == '\n') break; if (nch < max) { line[nch] = c; nch = nch + 1; } } if (c == EOF && nch == 0) return EOF; line[nch] = '\0'; return nch; }

• getline.c

Shell prompt

• Creating a distinguished prompt

  Nova 1%

  • The name of host, followed by space, followed by the command number, followed by the character '%' for normal user, or '#' for supperuser
  • hostname - show or set the system's host name

    hostname -f

Capitalizing first character

• Create a program capitalize

  #include <stdio.h> #include <ctype.h> int main() { int c; if ((c = getchar()) == EOF) return 0; putchar(toupper(c)); while ((c = getchar()) != EOF) putchar(c); return 0; }

• compile and link
• copy executable to ~/bin/ directory

Changing the csh prompt

• edit the ~/.cshrc file

  if ( $?prompt ) then if ( -o /bin/su ) then set prompt="`hostname -s | ~/bin/capitalize` \!# " else set prompt="`hostname -s | ~/bin/capitalize` \!% " endif endif

Assignment 1

• Singleton submission
• Header section in each source file

  /* .....
   * Full Name: your-full-name
   * Id No: your-id
   * User Name: your-user-name
   * Group No: your-group-number
   * Assignment No: the-assignment-number
   * .....
   */
  

• Make sure your name appears in the handson session list with the appropriate account name
• Automatic - compilation and execution logs will be sent automatically via email
• Manual - zip file with comments will be sent by the BODEK via email