To Lowercase

Task

Implement the function to_lowercase

• Take a UTF-8 encoded string and change it in-place so that any ASCII uppercase characters a-z are changed to their lowercase version
• Leave all other characters unchanged
• Return the number of characters updated from uppercase to lowercase

Function Signature

// Returns the number of characters lowercased and lowercases the capitalized 
// a-z ASCII characters of str in-place.
int32_t to_lowercase(char str[]);

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Examples

$ gcc to_lowercase.c -o to_lowercase
$ ./to_lowercase 
ABCDè
4 abcdè
éCLAIRE
6 éclaire
HELLO
5 hello
$ ./to_lowercase < small_input.txt
5 hello
3 Über
5 piÑata
0 ÜÖÅÑ
0 
1 aÜÖÅÑ
2 aÜÖÅÑb
1 ÜÖÅÑb
5 smÖrgÅs
0 😬

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Code

#include <stdint.h>
 
int32_t to_lowercase(char str[]){
	int32_t count = 0;
	for(int i = 0; str[i] != 0; i++){
		if((str[i] & 0x80) == 0 && (str[i] >= 'A' && str[i] <= 'Z')){
			count++;
			str[i] += ('a' - 'A');
		}
	}
	
	return count;
}