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PREV Write your own .... NEXT   (28 / 301)     Write C programs to implement the toupper() and the isupper() functions toUpper() int toUpper(int ch) {     if(ch>='a' && c<='z')         return('A' + ch - 'a');     else         return(ch); } isUpper() int isUpper(int ch) {     if(ch>='A' && ch <='Z')        return(1); //Yes, its upper!     else         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 :) ! #include <string.h> #define UPPER   "ABCDEFGHIJKLMNOPQRSTUVWXYZ" #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. ** PREV COMMENTS                                  INDEX                                  PRINT NEXT Last updated: November 3, 2005 www.cracktheinterview.com - Your destination for the most common IT interview questions, answers, frequently asked interview questions (FAQ), C Programs, C Datastructures for technical interviews conducted by the top IT companies around the world!