Character Processing

The Use of getchar() and putchar()
 getchar()
– Gets a character (an unsigned char) from stdin.
– It reads a character after you hit Enter key
• After you hit Enter key, all of characters move to stdin butter.
– getchar() returns a single char at a time.
c = getchar(); /* It stores c variable
after reading a char */
2

The Use of getchar() and putchar()
 putchar()
– Output a char on the screen.
[Ex]
#include <stdio.h> SKKU
int main(void)
{
putchar(‘S’);
putchar(‘K’);
Only one char is used
putchar(‘K’); in putchar(‘ ‘)
putchar(‘U’);
}
3

The Use of getchar() and putchar()
 Example
[Ex] [Ex]
c = getchar() ; while( (c=getchar()) != ‘ ’ )
while(c != ‘ ’ ) {
{ putchar( c ) ;
putchar( c ) ; }
c = getchar() ;
}
4

caps Program
 Example:
– Change uppercase to lowercase or lowercase to uppercase
#include <stdio.h>
int main(void)
{
while (( c = getchar() ) != ‘n’) {
if( ‘A’ <= c && c <= ‘Z’ )
putchar( c + (‘a’-’A’) ) ;
else if( ‘a’ <= c && c <= ‘z’ ) ;
putchar( c - (‘a’-’A’) ) ;
else
putchar( c ) ;
}
return 0;
}
5

The Macros in ctype.h
 ctype.h defines macros of character types.
Character macros
Macro Nonzero (true) is returned if
isalpha(c) c is a letter
isupper(c) c is an uppercase letter
islower(c) c is a lowercase letter
isdigit(c) c is a digit
isalnum(c) c is a letter or digit
isxdigit(c) c is a hexadecimal digit
isspace(c) c is a white space character
ispunct(c) c is a punctuation character
isprint(c) c is a printable charcter
isgraph(c) c is a printable, but not a space
iscntrl(c) c is a control character
isascii(c) c is an ASCII code
6

The Macros in ctype.h
 toupper() and tolower() functions
Character macros and functions
Function or macro Effect
toupper(c) Changes c from lowercase to uppercase
tolower(c) Changes c from uppercase to lowercase
toascii(c) Changes c to ASCII code
[Ex]
int tolower(int c); /* Return lowercase if ‘c’ is uppercase */
int toupper(int c); /* Return uppercase if ‘c’ is lowercase */
[Ex]
#define _tolower(c) ( (c) + ‘a’ – ‘A’ ) /* Define a function
using #define */
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caps Program
 Example:
– Changing uppercase to lowercase or lowercase to uppercase
#include <stdio.h>
#include <ctype.h>
int main(void)
{
while (( c = getchar() ) != ‘n’) {
if( isupper(c) )
putchar( tolower(c) ) ;
else if( islower(c) ) ;
putchar( toupper(c) ) ;
else
putchar( c ) ;
}
return 0;
}
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