#include <iostream>
#include <cstring>
#include <exception>

char read_from(const char* str, size_t elem) {
	if (!str || elem >= std::strlen(str))
		throw std::out_of_range("element out of range");

	return str[elem];
}

void write_to(char* str, char ch, size_t elem) {
	if (!str || elem >= std::strlen(str))
		throw std::out_of_range("element out of range");

	str[elem] = ch;
}

int main() {
	char lower[] { "abc?e" };
	char upper[] { "ABC?E" };
	auto upper_ptr { upper };

	lower[3] = 'd';
	upper_ptr[3] = 'D';

	auto letter_d { lower[3] };
	auto letter_D { upper_ptr[3] };

	std::cout << letter_d << "  " << letter_D << '\n';

	try {
		write_to(lower, 'z', 1);
		std::cout << read_from(lower, 1) << '\n';
	}
	catch (const std::out_of_range& oor ) {
		std::cout << "Error - " << oor.what() << '\n';
	}

	try {
		write_to(upper, 'z', 11);
		std::cout << read_from(upper, 11) << '\n';
	}
	catch (const std::out_of_range& oor) {
		std::cout << "Error - " << oor.what() << '\n';
	}
}

#include <cstdio>

int main()
{
    char lower[] = "abc?e";
    char upper[] = "ABC?E";
    
    char* upper_ptr = upper; // Equivalent: &upper[0]
    lower[3] = 'd'; // lower now contains a b c d e \0
    
    upper_ptr[3] = 'D'; // upper now contains A B C D E \0
    char letter_d = lower[3]; // letter_d equals 'd'
    
    char letter_D = upper_ptr[3]; // letter_D equals 'D'
    printf("lower: %s\nupper: %s", lower, upper);
    
    lower[7] = 'g'; // Super bad. You must never do this.
}

#include <iostream>
#include <string>
#include <memory>

int main()
{
   // char lower[] = "abc?e";
   std::string lower { "abc?e" };

   // char upper[] = "ABC?E";
   std::string upper { "ABC?E" };

   // added this here to show the original strings
   // printf("lower: %s\nupper: %s", lower, upper);
   std::cout << "lower: " << lower << "\nupper: " << upper << "\n\n";

   // char* upper_ptr = upper;
   char* upper_ptr { const_cast<char*> (upper.c_str()) };

   // another way is to use a unique_ptr....
   std::unique_ptr<std::string> upper_smt_prt { std::make_unique<std::string>(upper) };

   lower[3]     = 'd';
   upper_ptr[3] = 'D';

   char letter_d = lower[3];
   char letter_D = upper_ptr[3];

   std::cout << "lower: " << lower << "\nupper: " << upper << "\n\n";

   std::cout << upper_ptr << '\t' << *upper_smt_prt << '\n';

   // never ever do this, it will cause the universe to implode!
   // lower[7] = 'g';
}