C check if last character of string is equal with X

im writing a sketch for my arduino and i would like to check the last character of my string.

For example:

If the input is cats- i want to see if the last char (in my case is "-") is actualy -

The code im using:

The serial event function

void serialEvent() {
 while (Serial.available()) {
  // get the new byte:
  char inChar = (char)Serial.read(); 
  // add it to the inputString:
  inputString += inChar;
  // if the incoming character is a newline, set a flag
  // so the main loop can do something about it:
  if (inChar == '.') {
    stringComplete = true;
  } 
 }
}

This is checking if the input string is completed by checking the input is equals with -. However this is working only with the console because the python script im using is sending everything together

void loop() {
 if (stringComplete) {
 Serial.println(inputString);
 display.clearDisplay();
 display.setTextSize(1);
 display.setCursor(0,0);
 display.println("Altitude:");
 display.println(inputString);
 display.display();
 // clear the string:
 inputString = "";
 stringComplete = false;
}

Any idea on how to check it?