Interfacing an Altimeter that has Serial Output

Using Arduino Project Guidance
8

Combining the code already supplied gives you this:

int foo; // Useless declaration to molify the IDE
#define isdigit(X) (((X) >= '0') && ((X) <= '9'))

void setup()
{
  Serial.begin(9600);
}

void loop()
{
int AGL=read_int();
// Do math
}


int read_int()
{
static byte c;
static int i;

i = 0;
while (1)
  {
  while (!Serial.available())
    {;}
 
  c = Serial.read();
  
  if (c == '\r')
    {
    return i;
    }
  if (isdigit(c))
    {
    i = i * 10 + c - '0';
    }
  else
    {
    Serial.print("\r\nERROR: \"");
    Serial.print(c);
    Serial.println("\" is not a digit\r\n");
    return -1;
    }
  }
}

Compiled, not tested