Software 1 - getline, capitalize, ring (3)

administrivia

Web Page - http://www.cs.tau.ac.il/~efif/courses/Software1_Spring_03

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; }

• 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

• 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

• 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

#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;
}

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

ring

#include <stdio.h>

/*!
 * constants
 */

#define  WIDTH      60
#define  HEIGHT     60
#define  CENTER_X   30
#define  CENTER_Y   30
#define  R          20
#define  THRESHOLD  R

/*!
 * main
 */
int main()
{
  int x, y, val;

  for (y = 0; y < HEIGHT; y++) {
    for (x = 0; x < WIDTH; x++) {
      val = (y - CENTER_Y) * (y - CENTER_Y) +
        (x - CENTER_X) * (x - CENTER_X) - R * R;

      if (abs(val) < THRESHOLD)
        printf("%c", '#');
      else
        printf(" ");
    }
    printf("\n");
  }
  return  0;
}