240-222 Computer Programming Techniques Semester 1, 1998

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240-222 Computer Programming TechniquesSemester
1, 1998
4. Character Processing

• Objectives of these slides
• to look at how C processes characters

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Overview

• 1. Character Variables
• 2. Printing a Character
• 3. Reading a Character
• 4. Two Short Examples
• 5. A Skeleton for Character I/O
• 6. Counting Words

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1. Character Variables

• include ltstdio.hgtint main() char c /
  declare a character var / char c1 'A', c2
  'b', c3 '' c '1' return 0

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2. Printing a Character

• 2.1. Using printf()
• 2.2. Printing Funny Characters
• 2.3. Using putchar()

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2.1. Using printf()

• printf("c", 'a')printf("ccc", 'A', 'B',
  'C')
• A character can be treated as an integer
• Character 'a' 'b' 'A' 'B' '1' '2'
  '' . . .Integer 97 98 65 66 49 50
  38 . . .
• printf("d", 'a')printf("c", 97)

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2.2. Printing Funny Characters

• Name of char Written in C Integer
  valuealert \a 7backspace \b 8carriage
  return \r 13tab \t 9newline \n 10si
  ngle quote \' 39
• printf("c", '\a')/ the machine will beep /

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2.3. Using putchar() p.873

• include ltstdio.hgtint main()
  putchar('S') putchar('l') putchar('o')
  putchar('w') putchar('.') putchar('\n')
  return 0

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3. Reading a Character

• 3.1. Using getchar()
• 3.2. twice.c
• 3.3. Using twice.c

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3.1. Using getchar() p.873

• / Repeatedly input characters and print
  them twice on the screen /include
  ltstdio.hgtint main() char c while(1)
  / always true / c getchar()
  putchar(c) putchar(c) return 0

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3.2. twice.c

• / 2nd version /include ltstdio.hgtint
  main() int c while( (c getchar()) ! EOF
  ) putchar(c) putchar(c) return
  0

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• ((c getchar()) ! EOF)is not the same
  as (c (getchar() ! EOF))

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3.3. Using twice.c

• gcc -Wall -o twice twice.c
  twiceaabbccdd/ I typed abcd on the keyboard,
  followed by a carriage return and ltctrlgtd
  /

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Other Forms of Input / Output

• twice lt input.txtaaccddee / file contains
  acde /
• twice lt input.txt gt out.txt
• twice lt input.txt gtgt out.txt

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4. Two Short Examples

• 4.1. Copy a File
• 4.2. Capitalize and Double

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4.1. Copy a File (ccopy.c)

• / Copy from stdin to stdout a character at
  a time / include ltstdio.hgtint main() int
  c while ((c getchar()) ! EOF)
  putchar(c) return 0

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Compile and run

• gcc -Wall -o ccopy ccopy.c
• ccopy lt friends_proj.txt gt my_proj.txt

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4.2. Capitalize and Double (caps.c)

• Read characters from stdin to stdout
• capitalize lowercase letters
• double newlines

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• include ltstdio.hgtint main() int ch while
  ((ch getchar()) ! EOF) if ('a' lt ch
  ch lt 'z') putchar(ch 'A' - 'a')
  else if (ch '\n') putchar('\n')
  putchar('\n') else putchar(ch)
  return 0

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ASCII mapping from lower to upper

• 'a' 97 'A' 65'b' 98 'B' 66
  'z' 122 'Z' 90

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• / More portable version /include
  ltstdio.hgtinclude ltctype.hgt / p.859/520
  /int main() int ch while ((ch getchar())
  ! EOF) if (islower(ch))
  putchar(toupper(ch)) else if (ch '\n')
  putchar('\n') putchar('\n')
  else putchar(ch) return 0

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• / Third version /include ltstdio.hgtinclude
  ltctype.hgtint main() int ch while ((ch
  getchar()) ! EOF) if (ch '\n')
  putchar('\n') putchar('\n')
  else putchar(toupper(ch)) return 0

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5. A Skeleton for Character I/O

• / some comments /include ltstdio.hgtinclude
  ltctype.hgt / often required /int
  process_char(int ch)int main() int ch,
  new_ch while ((ch getchar()) ! EOF)
  new_ch process_char(ch) putchar(new_ch)
  return 0

continued
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• int process_char(int ch)/ manipulate the char
  as an integer / / do something to ch
  / return / an integer, representing a
  char /

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6. Counting Words

• / Count the words read from stdin. /include
  ltstdio.hgtinclude ltctype.hgtint
  found_next_word(void)int main() int word_cnt
  0 while (found_next_word() 1)
  word_cnt printf("Num words d\n",
  word_cnt) return 0

continued
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• int found_next_word(void)/ Skip spaces, then
  read the non-white space characters until
  white space is reached (or EOF). Return
  1 if found non-white space characters, 0
  otherwise. /....

continued
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• int found_next_word(void) int c while
  (isspace( c getchar() )) / skip white
  space / if (c ! EOF) / found a word /
  while ((c getchar()) !EOF
  !isspace(c)) / skip everything
  except EOF and white space / return
  1 return 0