Convert Uppercase Letters to Lowercase

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

void to_lowercase(char *str){
    int i = 0; 
    while(str[i] != '\0'){
        if(str[i] >= 'A' && str[i] <= 'Z'){
            str[i] = str[i] + ('a'-'A');
        }
        i++;
    }
}

int main(){
    char str[100];
    fgets(str, sizeof(str), stdin);

    int i = 0;
    while(str[i]){
        if(str[i] == '\n') {str[i] = '\0'; break;}
        i++;
    }
    to_lowercase(str);
    printf("%s", str);
    return 0;
}