Saturday, July 7, 2007

Write C programs to implement the toupper() and the isupper() functions.


int toUpper(int ch)
if(ch>='a' && c<='z')
return('A' + ch - 'a');


int isUpper(int ch)
if(ch>='A' && ch <='Z')
return(1); //Yes, its upper!
return(0); // No, its lower!

Its important to know that the upper and lower case alphabets have corresponding integer values.

A-Z - 65-90
a-z - 97-122

Another way to do this conversion is to maintain a correspondance between the upper and lower case alphabets. The program below does that. This frees us from the fact that these alphabets have a corresponding integer values. I dont know what one should do for non-english alphabets. Do other languages have upper and lower case letters in the first place :) !


#define LOWER "abcdefghijklmnopqrstuvwxyz"

int toUpper(int c)
const char *upper;
const char *const lower = LOWER;

// Get the position of the lower case alphabet in the LOWER string using the strchr() function ..
upper = ( ((CHAR_MAX >= c)&&(c > '\0')) ? strchr(lower, c) : NULL);

// Now return the corresponding alphabet at that position in the UPPER string ..
return((upper != NULL)?UPPER[upper - lower] : c);

Note that these routines dont have much error handling incorporated in them. Its really easy to add error handling to these routines or just leave it out (as I like it). This site consciously leaves out error handling for most of the programs to prevent unwanted clutter and present the core logic first.

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