Bitwise

#include<stdio.h>
char to_upper(char ch)
{
    return ch & 95;
}
char to_lower(char ch)
{
    return ch | 32;
}

int main()
{
    char *str="AbCdEfGhIjKlMnOpQrStUvWxYz";
    int i;
    for(i=0; i<26; i++){
        printf("Uppercase: %c, ", to_upper(str[i]));
        printf("lowercase: %c\n", to_lower(str[i]));
    }

    return 0;
}