Validate characters are less than specified letter in alphabet c++ - c++

Question

I am making a function that validates a user input is a grid reference, between A0 and J9 (a 10 x 10 grid).
I can validate the integer part fine, but am wondering how to validate the alphabetical part, without saying for example:
if(Column == 'A' || Column == 'a' || Column == 'B' ....)
In a similar fashion to saying if int Row < 10.
Also, is there a way to convert to a single character, such as stoi for string to integer?
Here is my functions code, thank you.
void InputLocation(){
bool still_prompt = true;
while (still_prompt)
{
std::string answer;
std::cout << "Enter a grid location from A0 to J9" << std::endl;
std::getline(std::cin, answer);
std::string Column = answer.substr(0, 1);
std::string Row = answer.substr(1, 1);
if (answer.length() > 2 || answer.length() < 2){
std::cerr << "Location input must be of length 2 characters.\n";
continue;
}
else{ // If input has length 2, then get to this stage
try{
int intRow = std::stoi(Row);
if (intRow < 0 || intRow > 9){
std::cerr << "Row number must be between 0 and 9. \n";
continue;
}
}
catch (...){
std::cerr << "Second character of location input must be integer. \n";
continue;
}
}still_prompt = false;
}
}

Answer 1

Individual characters can be treated as numbers, so this is pretty simple to do! For example:
bool test(char character) {
return 'a' <= character && character <= 'j';
}
This function tests if a character is between 'a' and 'j'. This works because under the hood, 'a' and 'j' are just numbers. You can even see what numbers they are just by printing out the value:
int a_value = 'a'; // chars can be implictly converted to int
int j_value = 'j';
std::cout << "value of 'a'": << a_value << '\n';
std::cout << "value of j'j": << j_value << '\n';
Putting it all together. We can check if something is in the correct range just by doing a comparison. The following function will check if a character is within the range a through j.
bool testInRange(char c) {
return ('a' <= c && c <= 'j') || ('A' <= c && c <= 'J');
}
We can also write a function to convert it into an index on the grid:
int charToGridIndex(char c) {
if('A' <= c && c <= 'J')
{
return c - 'A';
}
else if('a' <= c && c <= 'j')
{
return c - 'a';
}
else
{
// Return -1 to indicate an invalid character
return -1;
}
}
Here,
charToGridIndex('a') == 0
charToGridIndex('b') == 1
charToGridIndex('c') == 2
charToGridIndex('d') == 3
charToGridIndex('e') == 4
charToGridIndex('f') == 5
charToGridIndex('g') == 6
charToGridIndex('h') == 7
charToGridIndex('i') == 8
charToGridIndex('j') == 9