Const and calculation problem

/* 
    qbcan CanSat example.

    This sketch reads temperature and pressure data and sends it to the Ground station
*/

//Include the required libraries
#include <qbcan.h>
#include <Wire.h>
#include <SPI.h>

//Pressure sensor object
BMP180 bmp;

//Radio Parameters
#define NODEID        2    //unique for each node on same network
#define NETWORKID     100  //the same on all nodes that talk to each other
#define GATEWAYID     1    //Receiving node
#define ENCRYPTKEY    "sampleEncryptKey" //exactly the same 16 characters/bytes on all nodes!


const TempGradient = -0,0065;
const StartPressure = 1019;
const StartTemp = 283,15;
const StartAltitude = 10;
const GasConstant = 287,06;
const GravAcceleration = 9,81;


//Radio object
char payload[50];
RFM69 radio;

void setup()
{
  //Initialize serial connection for debugging
  Serial.begin(9600);
  Serial.println("REBOOT");

  // Initialize pressure sensor.
  if (bmp.begin())
    Serial.println("BMP180 init success");
  else
  {
    //In case of error let user know of the problem
    Serial.println("BMP180 init fail (disconnected?)\n\n");
    while(1); // Pause forever.
  }

  //Initialize radio
  radio.initialize(FREQUENCY,NODEID,NETWORKID);
  radio.setHighPower(); //To use the high power capabilities of the RFM69HW
  radio.encrypt(ENCRYPTKEY);
  Serial.println("Transmitting at 433 Mhz");

}

void loop()
{
  double T,P;
  
  // Get a new pressure reading:
  bmp.getData(T,P);
  
  long Temp = (T,2);
  long Pressure = (P,2);

  
  //Display data
  Serial.print("Absolute pressure: ");
  Serial.print(P,2);
  Serial.println(" mb.");
  Serial.print("Temperature: ");
  Serial.print(T,2);
  Serial.println(" deg C.");
  
  
  // Calculate Altitude
  Altitude = (StartTemp/TempGradient)*(pow((Pressure/StartPressure),(-TempGradient*GasConstant/GravAcceleration))-1)+ StartAltitude

  // Display Altitude
  Serial.print("Altitude: ");
  Serial.print(Altitude);
  Serial.println(" meters high"); 
 
  //Send Data
  sprintf(payload,"T: %d C, P: %d mb.",(int)T,(int)P);
  Serial.println(payload);
  radio.send(GATEWAYID, payload, 50);
  Serial.println("Send complete");
  
  delay(500);
}

There are the following errors:

Arduino: 1.8.1 (Windows 10), Board:"SparkFun Pro Micro, ATmega32U4 (5V, 16 MHz)"

CanSat_-_With_Altitude_V1:22: error: 'TempGradient' does not name a type

 const TempGradient = -0,0065;

       ^

CanSat_-_With_Altitude_V1:23: error: 'StartPressure' does not name a type

 const StartPressure = 1019;

       ^

CanSat_-_With_Altitude_V1:24: error: 'StartTemp' does not name a type

 const StartTemp = 283,15;

       ^

CanSat_-_With_Altitude_V1:25: error: 'StartAltitude' does not name a type

 const StartAltitude = 10;

       ^

CanSat_-_With_Altitude_V1:26: error: 'GasConstant' does not name a type

 const GasConstant = 287,06;

       ^

CanSat_-_With_Altitude_V1:27: error: 'GravAcceleration' does not name a type

 const GravAcceleration = 9,81;

       ^

C:\Users\Lars\Desktop\Cansat\Code\CanSat_-_With_Altitude_V1\CanSat_-_With_Altitude_V1.ino: In function 'void loop()':

CanSat_-_With_Altitude_V1:77: error: 'Altitude' was not declared in this scope

   Altitude = (StartTemp/TempGradient)*(pow((Pressure/StartPressure),(-TempGradient*GasConstant/GravAcceleration))-1)+ StartAltitude

   ^

CanSat_-_With_Altitude_V1:77: error: 'StartTemp' was not declared in this scope

   Altitude = (StartTemp/TempGradient)*(pow((Pressure/StartPressure),(-TempGradient*GasConstant/GravAcceleration))-1)+ StartAltitude

               ^

CanSat_-_With_Altitude_V1:77: error: 'TempGradient' was not declared in this scope

   Altitude = (StartTemp/TempGradient)*(pow((Pressure/StartPressure),(-TempGradient*GasConstant/GravAcceleration))-1)+ StartAltitude

                         ^

CanSat_-_With_Altitude_V1:77: error: 'StartPressure' was not declared in this scope

   Altitude = (StartTemp/TempGradient)*(pow((Pressure/StartPressure),(-TempGradient*GasConstant/GravAcceleration))-1)+ StartAltitude

                                                      ^

CanSat_-_With_Altitude_V1:77: error: 'GasConstant' was not declared in this scope

   Altitude = (StartTemp/TempGradient)*(pow((Pressure/StartPressure),(-TempGradient*GasConstant/GravAcceleration))-1)+ StartAltitude

                                                                                    ^

CanSat_-_With_Altitude_V1:77: error: 'GravAcceleration' was not declared in this scope

   Altitude = (StartTemp/TempGradient)*(pow((Pressure/StartPressure),(-TempGradient*GasConstant/GravAcceleration))-1)+ StartAltitude

                                                                                                ^

CanSat_-_With_Altitude_V1:77: error: 'StartAltitude' was not declared in this scope

   Altitude = (StartTemp/TempGradient)*(pow((Pressure/StartPressure),(-TempGradient*GasConstant/GravAcceleration))-1)+ StartAltitude

                                                                                                                       ^

exit status 1
'TempGradient' does not name a type

This report would have more information with
"Show verbose output during compilation"
option enabled in File -> Preferences.

I don’t understand why the constants don’t work and why the Altitude calculation doesn’t also.
Please help, I don’t know people irl who understand Arduino.

LuckyBuck:
I don't understand why the constants don't work ...

Because you haven't specified what type (uint8_t, int, long, float, etc) you want them to be.

 const TempGradient = -0,0065;

In addition to the above comment, what is the comma supposed to do?

jremington:

 const TempGradient = -0,0065;

In addition to the above comment, what is the comma supposed to do?

It's supposed to be a decimal point.

When programming, one must remember to "be American" and use a decimal dot, not a decimal comma.