Convert Uppercase Letters to Lowercase

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

void to_lowercase(char *str) {
    int index = 0;
    char offset = 'a' - 'A';

    while (str[index] != '\0') {
        char ch = str[index];
        if (ch >= 'A' && ch <= 'Z') {
            // we have an uppercase char -> convert it
            str[index] = ch + offset;
        }
        index++;
    }
}

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;
}