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/*
 * case_conv.c  -   Program to change case without using arithmetic
 *                  operators or library functions.  This program
 *                  works ONLY if the charcter set is ASCII, and hence
 *                  is not portable.  It is here, only as an example,
 *                  to convey a logic as how it can be done.
 */

/*
 * Refer the ASCII table while tracing the following program:
 *
 * Letter           Upper(binary)       Lower(binary)
 * ——           ————-       ————-
 *
 *  A               0100 0001           0110 0001
 *  B               0100 0010           0110 0010
 *  …             …                 …
 *  O               0100 1111           0110 1111
 *  P               0101 0000           0111 0000
 *  …             …                 …
 *  Z               0101 1010           0111 1010
 */

#include <stdio.h>
#include <stdlib.h>

int
to_lower ( int ch )
{
    unsigned char _ch = (unsigned char)ch >> 4;

    /* If CH is already in lower case, return it */
    if ( _ch == 0×6 || _ch == 0×7 )
        return ch;

    /* convert it to lower case */
    if ( _ch == 0×4 )
        return (int)( ( (unsigned char)ch & 0×0f ) | 0×60 );
    else
    if ( _ch == 0×5 )
        return (int)( ( (unsigned char)ch & 0×0f ) | 0×70 );
    else
        return ch;
}

int
to_upper ( int ch )
{
    unsigned char _ch = (unsigned char)ch >> 4;

    /* If CH is already in upper case, return it */
    if ( _ch == 0×4 || _ch == 0×5 )
        return ch;

    /* convert it to upper case */
    if ( _ch == 0×6 )
        return (int)( ( (unsigned char)ch & 0×0f ) | 0×40 );
    else
    if ( _ch == 0×7 )
        return (int)( ( (unsigned char)ch & 0×0f ) | 0×50 );
    else
        return ch;
}

int
main ( void )
{
    printf ( "%c\n", to_upper ( ‘+’ ) );
    printf ( "%c\n", to_upper ( ‘r’ ) );
    printf ( "%c\n", to_upper ( ‘l’ ) );
    printf ( "%c\n", to_upper ( ‘P’ ) );

    printf ( "%c\n", to_lower ( ‘$’ ) );
    printf ( "%c\n", to_lower ( ‘R’ ) );
    printf ( "%c\n", to_lower ( ‘O’ ) );
    printf ( "%c\n", to_lower ( ‘9′ ) );
    return EXIT_SUCCESS;
}

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Related Blog Items

• Unsigned long to string (ultostr)
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• How the keyboard works?
• C++ Basics Tutorial - Lesson 2
• Unsigned long long (uint64) to string (ulltostr)

This entry was written by Vijay Zanvar and posted on February 16, 2007 at 1:09 pm and filed under Bits & Bytes Manipulation, C Tidbits, Generic Programming. Bookmark the permalink. Follow any comments here with the RSS feed for this post. Post a comment or leave a trackback: Trackback URL.