serialreaidng.c

char NMEA_string[70] = "";
char buffer = 0;
int n = 0;
int state = 0;
 
while (1){
  buffer = Serial.read(); // Read Character
 
  switch(state){
    case 0: // Waiting for a $
      if (buffer == '$'){
        state=1;
        n=0;
        memset(NMEA_string,0,70); // Clear NMEA_sentence
        NMEA_string[n++]=buffer;
      }
    break;
    case 1:   // Got a string
      if (buffer == '\r'){  // End of string
        // Parse the string
        state=0;
      } else {
        NMEA_string[n++]=buffer;
      }
      if (buffer >=68) {  // Stop at 68 (69 chars) so there's still a NULL at the end.
        printf("Error: NMEA_sentence has overflown (%s)\n", NMEA_sentence);
        state=0;
      }
    break;
  } // Close switch
} // Close while