CS113%20Introduction%20to%20C

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CS113Introduction to C

• Instructor Ioannis A. VetsikasE-mail
  vetsikas_at_cs.cornell.edu
• Lecture 11 September 18

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The C preprocessorConditional Inclusion

• if, elif, else, endif
• Allow us to define conditional statements for
  what the compiler should compile
• define name and undef name
• defined(name) returns 1 if name is defined with a
  define statement and 0 otherwise
• ifdef and ifndef are same respectively as if
  defined and if !defined
• ifdef DEBUG
• printf(Debug mode)
• i
• else
• printf(Real mode)
• endif

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Streams

• I/O done through streams two kinds text and
  binary
• Text streams are sequences of lines, each of
  which is a sequence of characters terminated by a
  newline
• Binary streams are sequences of characters
  corresponding to internal representation of data.
• Streams created by opening files and referenced
  using stream pointers (FILE )
• Normally three standard streams are automatically
  open
• stdin (stream for standard input - from keyboard)
• stdout (stream for standard output - to screen)
• stderr (stream for standard error output - to
  screen)

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Functions for opening closing

• Open a file
• FILE fopen(char name, char mode)
• Opens file with name name using mode mode
• Mode is taking values r (open text for
  reading), w (open text for writing), etc
• For binary files add b at the end, e.g. rb
  (open binary for reading)
• Usage FILE fpfopen(infile, r)
• Returns NULL if some problem occurs during the
  opening of the file (e.g. file is not found, or
  permissions are not set correctly etc.)
• Close a file
• int flcose(FILE fp)

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Some other functions

• Defined in ltstdio.hgt
• int fprintf(FILE fp, char format, )
• int fscanf(FILE fp, char format, )
• int fgetc(FILE fp)
• int fputc(int c, FILE fp)
• char fgets(char s, int n, FILE fp)
• int fputs(char s, FILE fp)
• int feof(FILE fp)
• For more functions read appendix B of the KR book

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Example (from KelleyPohl - modified)

• include ltstdio.hgt
• include ltstdlib.hgt
• void double_space(FILE ifp, FILE ofp)
• int c
• while ((cgetc(ifp)) ! EOF)
• putc(c, ofp)
• if (c\n)
• putc(\n, ofp) / duplicate Newline /
• int main(int argc, char argv)
• FILE ifp fopen(argv1, r)
• FILE ofp fopen(argv2, w)
• double_space(ifp, ofp)
• fclose(ifp)
• fclose(ofp)

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Announcements

• Wednesday Mock quiz
• Friday Quiz (the real one) Make sure you come
• We are done with covering the KR book
• Read the appendices by yourselves and look
  especially at appendix B where the library
  functions are presented
• Homework 4 is challenging and you should start as
  early as possible Ill announce extra office
  hours for the next week to allow you to come and
  talk to me about the homework
• I will do some revision, answer questions and do
  miscellaneous programming (debugging) skills next