Simplifying a function based on matching the pattern of a string - c++

Question

Question: I'm new to C++ and after writing the following code seems like there should be a way to shorten it. Maybe by somehow matching the string? How would this be done?
The function takes a string message received via Serial port and sets the value of a particular element of the pinValues[] array depending on the message. The value that will be set is determined by the last character H or L just before the \n.
String pattern: (a number)(H or L)\n
Eg: message == "4H\n" will set the 5th element pinValues[4] to HIGH. The number at the start of the string can be 1 to 2 digits.
void setPinValues(String message) {
if( message == "1H\n" ) {
pinValues[1] = HIGH;
}
if( message == "1L\n" ) {
pinValues[1] = LOW;
}
if( message == "2H\n" ) {
pinValues[2] = HIGH;
}
if( message == "2L\n" ) {
pinValues[2] = LOW;
}
if( message == "3H\n" ) {
pinValues[3] = HIGH;
}
if( message == "3L\n" ) {
pinValues[3] = LOW;
}
if( message == "4H\n" ) {
pinValues[4] = HIGH;
}
if( message == "4L\n" ) {
pinValues[4] = LOW;
}
if( message == "5H\n" ) {
pinValues[5] = HIGH;
}
if( message == "5L\n" ) {
pinValues[5] = LOW;
}
if( message == "6H\n" ) {
pinValues[6] = HIGH;
}
if( message == "6L\n" ) {
pinValues[6] = LOW;
}
}

Answer 1

This is probably not the official "C++"-approved way of doing it, but you could do:
unsigned int pinNo = 0;
unsigned char level = 0;
int result = sscanf(message.c_str(), "%u%c", &pinNo, &level);
if (result < 2)
// it failed
if (pinNo > 6)
// bad data
levelVal = (level == 'H') ? HIGH : LOW;

Answer 2

I'd do some sanity checking on the string while extracting the key and value from the first two chars. If you don't need to sanity check the message, it could be as short as
void setPinValues(String message) {
pinValues[ message[0] - '0' ] = (message[1] == 'H') ? HIGH:LOW;
}
Although you may want to make that a little longer, i.e. check the string length, and that the 2 chars your checking are in the right range. i.e
void setPinValues(string message) {
if (
message.size() >= 2
and
message[0] >= '1' and message[0] <= '6'
and (message[1]=='H' or message[1]=='L')
) {
pinValues[ message[0] - '0' ] = (message[1] == 'H') ? HIGH:LOW;
}
}
EDIT: you could also extend that to checking two leading digits, i.e.
int n, off=0;
if ( s[off] <= '9' and s[off] >= '0')
{
n = s[off++] - '0';
}
if ( s[off] <= '9' and s[off] >= '0')
{
n = 10*n + s[off++] - '0';
}
if (off > 0 and (s[1]=='H' or s[1]=='L')) {
pinValues[ message[0] - '0' ] = (message[1] == 'H') ? HIGH:LOW;
}

Answer 3

Assuming String is actually a std::string or has an identical interface, and also assuming an ASCII-compatible character set...
void setPinValues(String message) {
const size_t sz = message.size();
// input validation, ignore the message if it doesn't fit the pattern
// you can remove this "if" block if the message has already been validated
if ( (sz < 3) || (sz > 4)
// note how message[0] will be checked twice if sz == 3
// once as message[0] and once as message[sz -3]
// but if sz == 4 we check message[0] and message[1]
|| (message[0] < '0') || (message[0] > '9')
|| (message[sz - 3] < '0') || (message[sz - 3] > '9')
|| ((message[sz - 2] != 'H') && (message[sz - 2] != 'L'))
|| (message[sz - 1] != '\n'))
return;
// convert the first or two characters to a number
int pinNumber = message[0] - '0';
if (sz == 4)
pinNumber = (pinNumber * 10) + (message[1] - '0');
// additional check to verify the pin number is in the correct range
if ((pinNumber < 1) || (pinNumber > 6))
return;
// apply
pinValues[pinNumber] = (message[sz - 2] == 'H' ? HIGH : LOW);
}