Exercise 2.10 - upper case letters to lower case¶

Question¶

Rewrite the function lower, which converts upper case letters to lower case, with a conditional expression instead of if-else.

/* Function lower(c) using conditional expression */

#include <stdio.h>

int lower(int c);

int main(void) {
    int c;

    while ((c = getchar()) != EOF) {
        putchar(lower(c));
    }
}

int lower(int c) { return c >= 'A' && c <= 'Z' ? c + 'a' - 'A' : c; }

Explanation¶

In this program we are going to convert upper case letters to lower case. We declare a function called lower in the beginning of the program. When the program enters the while loop it each character it gets to lower:

while((c=getchar())!=EOF)
{
        putchar(lower(c));
}

The lower function checks for all the uppercase characters and prints everything in the lowercase. It does this by a conditional statement, where if a upper case character is found, it subtracts ‘A’ to get relative index, adds it to ‘a’ to return corresponding smaller case character, if a lower case character is found, it is simply returned:

return c>='A' && c<='Z'? c+'a'-'A':c;