Convert Uppercase Letters to Lowercase

Find out letter number/position wrt 'A'

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

void to_lowercase(char *str) {
    char curr;
    while(*str){
        curr = *str;
        if(curr >= 'A' && curr <= 'Z'){
           curr = curr - 'A' + 'a';
           *str = curr; 
        } 

        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;
}

Solving Approach