Convert Uppercase Letters to Lowercase

#include <stdio.h>
#include <stdint.h>

#define UPPER_START ('A')
#define UPPER_END ('Z')
#define LOWER_START ('a')
#define LOWER_END ('z')
#define UPPER_LOWER_DIFF (LOWER_START-UPPER_START)
void to_lowercase(char *str) {
    // Your logic here
    while(*str)
    {
        if((*str >= UPPER_START) && (*str <= UPPER_END))
        {
            *str = *str + UPPER_LOWER_DIFF;
        }
        str++;
    }
}

int main() {
    char str[101];
    fgets(str, sizeof(str), stdin);

    // Remove newline
    uint8_t i = 0;
    while (str[i]) {
        if (str[i] == '\n') {
            str[i] = '\0';
            break;
        }
        i++;
    }

    to_lowercase(str);
    printf("%s", str);
    return 0;
}